Hoarding Disorder: Development in Conceptualization, Intervention, and Evaluation

Hoarding has received a great deal of public attention, especially with the proliferation of reality TV shows dedicated to the subject. Popular media portrayals of hoarding present a relatively straightforward issue with a similarly straightforward solution: “just clean it up.” However, in contrast to such sensationalist depictions, hoarding disorder is a recognized mental health condition that has been the subject of systematic empirical study in psychology, psychiatry, and related fields for nearly 2 decades. As early as 1947, Erich Fromm described a “hoarding orientation” in which a person’s security depended on collecting and saving objects. In 1962, Scandinavian psychiatrist Jens Jansen referenced “collector’s mania” to describe older adults who filled their rooms with an overabundance of objects.

In 1996, Frost and Hartl (1) defined hoarding as having three main characteristics:

This definition became the foundation for the development of the diagnostic criteria for hoarding disorder. Current conceptualizations of hoarding describe it as a condition that involves the excessive accumulation of possessions in the home, combined with difficulty discarding such items that most other people would not keep (2).

In 2013, the American Psychiatric Association (3) recognized hoarding as a unique disorder among obsessive-compulsive spectrum disorders. Six diagnostic criteria must be met for a patient to receive a diagnosis of hoarding disorder, which is currently classified under the code for obsessive-compulsive disorder (OCD; 300.3) (Box 1). Two specifiers provide descriptive ratings for both the acquiring and insight aspects of hoarding.

Historically, hoarding was considered a subtype of OCD, although recent evidence suggests that there are more differences than similarities. Hoarding behaviors have been identified among individuals with anxiety disorders other than OCD, particularly those diagnosed as having generalized anxiety disorder or social phobia (4). Major depressive disorder, generalized anxiety disorder, and social phobia have also been found to be more prevalent among individuals with hoarding disorder than those with OCD (4). Another important characteristic of hoarding disorder that differentiates it from OCD is that the person engaging in hoarding is typically not troubled by the symptoms of the disorder, despite the obviousness of the problem to others. In contrast, people with OCD tend to have higher levels of insight, more often expressing distress at the behavioral and cognitive symptoms of the disorder (2). These differences suggest that hoarding disorder is not a subtype of OCD but rather a distinct condition that is often related to other psychiatric conditions (4).

Hoarding is a common condition, affecting approximately 2%–6% of the adult population in global north countries (5–7). Epidemiological studies indicate that hoarding occurs in both women and men at similar rates (5). People with hoarding disorder tend to live alone and are less likely to have family or friends visit their home (8). In our clinical experience, people who hoard have sometimes reported a preference for being alone with their objects, indicating more reliable relationships with objects than with people. Defining the average age of onset of hoarding is complicated by a lack of consistent diagnostic criteria and varied use of an array of assessment instruments. A recent meta-analysis found that the mean age of onset of hoarding symptoms across studies was 16.7 years (7). Severity of hoarding symptoms tended to worsen over time.

Treatment of people who hoard is made more complex by substantial clinical comorbidity. More than 60% of people with clinically significant hoarding meet the criteria for at least one co-occurring psychiatric disorder (9). Studies of hoarding comorbidity have reported particularly high rates of major depressive disorder (50%–52%), generalized anxiety disorder (24%), and social phobia (23%) (4). The symptomology associated with depressive and anxiety disorders has been suggested to play a role in reinforcing the negative emotional states that maintain hoarding disorder (9). For example, a person experiencing a major depressive episode that provokes general behavioral deactivation may have difficulty discarding. As such, differentiating hoarding disorder from hoarding symptoms caused by another mental illness can be challenging (10), and treatment of hoarding disorder is further complicated by substantial clinical comorbidity.

On an individual level, accumulated possessions can result in difficulty completing basic functions, such as socializing, preparing food, bathing, and mobilizing when rooms and hallways become inaccessible from clutter (11). Recent research indicates that hoarding disorder significantly affects employment because people who hoard take an average of 7 days off from work a month for psychiatric reasons: a number equal to that of people with bipolar and psychotic disorders and significantly higher than for individuals with mood disorders (12). These negative outcomes also affect those living with the affected individual. Severely cluttered family environments are associated with increased childhood distress, reduced social interaction, and greater family conflict (12).

It is important to note, however, that hoarding is distinct from other anxiety-based disorders because its implications pose problems not only for the individual with the disorder and their family, but also for broader society (2). Specifically, problems associated with hoarding behavior provoke health and safety concerns for both the occupant of the home and for those who live nearby, such as neighbors with shared walls (13). For example, risk of fire increases when combustibles are stored near heat sources or electrical wiring, and blocked exits create safety hazards for residents and emergency responders (11). A study by Lucini et al. (13) found that 60% of hoarding-related fires spread beyond its source, in contrast with only 10% of nonhoarding fires.

In addition to fire risk, severe hoarding behavior can also result in degradation of the home, with routine maintenance neglected, and homes becoming squalid, moldy, pest-infected, or structurally unsound because of excessive weight of clutter or water damage (11). When possessions expand beyond the confines of the home to create unsightly clutter in the backyard or on the front porch, laws and regulations requiring the upkeep of “tidy premises” of a home’s exterior may be violated (2). Other legal ramifications can include the involvement of child welfare services, older adult and guardianship services, and animal welfare organizations (2, 14). Thus, given the social problems that hoarding creates, treatments for this issue expand beyond clinical focus on the person with the diagnosis alone to involving a multiagency approach that targets both the home and the potential impacts on the broader community (2).

Assessments for Hoarding Behaviors

Given that hoarding is a complex condition with varied symptoms and associated features, both clinicians and patients benefit from a rapid but comprehensive assessment. Establishing a diagnosis of hoarding disorder facilitates conversations about the meaning of this psychiatric condition and enables access to third-party payments for services. Determining the severity of hoarding behaviors (i.e., acquiring, difficulty discarding, clutter throughout the home and in other spaces) helps to establish intervention targets and the potential barriers to treatment. Detailed assessment of the degree of functional impairment from hoarding demonstrates the personal cost to the patient and indicates whether the clinician should be concerned about the patient’s health or safety. It also provides a ready avenue for motivational conversations about resolving frustrating functioning difficulties.

A detailed hoarding interview (15) facilitates collection of information about hoarding symptoms, as well as general life circumstances, housing conditions, social and family life, history of hoarding, and other problems. It facilitates the development of a conceptual model for each patient’s hoarding symptoms and clarifies where to start the work (e.g., on acquiring habits or on dangerous clutter in particular areas). As the reliability of self-ratings of hoarding severity can be compromised by decreased insight, a multi-informant approach carried out by an expert clinician is generally recommended (16).

The most commonly used hoarding assessment instruments (17–31), which have all been found to be reliable and valid for use with clinical hoarding populations, are summarized in Table 1. In addition to these measures that assess hoarding symptom severity as well as clutter, several tools examine the home environment. One example is the HOMES Multidisciplinary Risk Assessment (26), a brief structured tool that assesses health and mental health difficulties, safety of others, obstacles to movement in the home, as well as structural concerns related to blocked paths, heat sources, and so forth. Another example is the Environmental Cleanliness and Clutter Scale (32), which is used to score levels of uncleanliness and clutter in one’s living environment. Additionally, the Home Environment Index (33) examines squalor (e.g., domestic and personal hygiene) among clients with hoarding, as well as the related effects on daily activities and tasks.

Behavioral tasks are also used to assess for aspects of hoarding, including acquiring, difficulty discarding, and categorization. Such tasks include computerized tasks of acquiring and discarding (e.g., 34), categorization tasks with personal and nonpersonal items (e.g., 35), and interpretive bias tasks (based on ambiguous hoarding-related scenarios and hoarding beliefs) (36). Behavioral measures do not depend on the participant’s level of insight, in contrast to self-report tools, and may enhance understanding of hoarding symptomatology, severity, and underlying factors beyond what is perceived and explicitly reported by the participant.

Models and Mechanisms for Hoarding

Animal Models

Preliminary investigations into using animal models to understand hoarding behavior in humans have begun in a limited capacity. Andrews-McClymont et al. (37) compared data on human hoarding with hoarding behaviors in a variety of animal species. They found that rodent models of hoarding had the greatest overlap with human traits. Both species’ hoarding behaviors increased with age, and both had evidence of abnormalities in the same regions of the brain (37).

Neurobiological and Genetic

Hoarding behavior may be due to neuropsychological conditions with specific brain pathology (e.g., dementia, stroke, another medical or mental health condition) or may exist without neuropathology. Studies indicate that the ventromedial prefrontal cortex is linked to hoarding behavior (38); this region of the brain is involved in decision making as well as emotional processing of rewards and punishments.

Early neuroimaging studies of hoarding were focused on patient samples with OCD. The initial study of hoarding without known brain pathology (nonorganic hoarding) utilized position emission tomography to examine patients with OCD (N=45), including some with (N=33) and some without (N=12) hoarding symptoms, as well as a healthy control group (N=17) (39). This study found that those with OCD and hoarding showed less glucose metabolism in the posterior cingulate cortex and dorsal anterior cingulate cortex. Such regions are associated with decision making, categorization, and implicit learning (40).

Other initial studies used functional magnetic resonance imaging (fMRI) with tasks such as imagining discarding a pictured item with patients with OCD with (N=13) and without (N=16) hoarding, as well as a control group (N=21). Study participants with OCD and hoarding showed greater activation in bilateral anterior ventromedial prefrontal cortex compared with the other two groups (41). These studies are limited in that they included OCD samples, so they may be less generalizable to patients with hoarding disorder who do not also have OCD.

Research focusing on individuals with primary hoarding disorder also used fMRI, which demonstrated abnormalities in brain function in several regions. One study, which included 12 participants with hoarding disorder and 12 healthy control participants, used a decision-making task whereby the participants selected personal (those brought to study by the participant) versus nonpersonal paper items to discard, which were then shredded. During the decision making, patients with hoarding disorder showed greater activation of the lateral orbitofrontal cortex and parahippocampal gyrus compared with the healthy control group (42).

A larger follow-up study, which included 43 patients with hoarding disorder, 31 patients with OCD, and 33 healthy control patients, incorporated the same decision-making task in which the shredding of discarded paper items occurred at the end of the session (43). When those with hoarding disorder made decisions about personal items, brain activity was higher in the anterior cingulate cortex and insula, whereas patients with hoarding disorder showed lower brain activity compared with the OCD and control groups when making decisions regarding nonpersonal items (43). These regions are involved in emotional responses and affective states. These findings suggest that increases and decreases in brain activity varied by the specifics of the task (whether personal items were included) and demonstrated distinctions in abnormalities in brain activity related to OCD and hoarding disorder (44).

These researchers also conducted a small pilot study (43) of a simulated discarding and acquiring decision-making task using fMRI with patients with hoarding disorder (N=6) and a healthy control group (N=6). This task replicated abnormalities in activation of the frontotemporal region associated with discarding tasks, as well as some of these same abnormalities when making decisions to acquire. A recent study (44) of participants with hoarding disorder (N=79) and a control group (N=44), which included images of high- or low-value objects, also found overactivity in the anterior cingulate cortex when participants made decisions regarding personal objects and acquiring objects. Levy et al. (45) found neurological abnormalities among participants with hoarding disorder even at resting state.

These neuroimaging studies and other research suggest that people with hoarding disorder experience cognitive challenges and related impairments (20, 44, 45). A core component of the cognitive-behavioral model of hoarding (15) includes challenges with information processing, specifically impairments in the areas of working memory (46), inattention and distractibility (47, 48), self-control (49, 50), decision making (51), as well as categorizing personal belongings (35, 52). Such challenges are evidenced through studies that used neuropsychological tests as well as self-report measures (20). Studies also suggest that cognitive impairments may be specific to hoarding while also being at least somewhat related to comorbid conditions such as anxiety, depression, and stress (20).

Future studies may examine cognitive (e.g., planning, attention) and affective (e.g., emotion, visceral information, salience, and valence) decision making among those with hoarding disorder as well as cognitive impairments evidenced by neuropsychological tests. Those with poor cognitive confidence or perceived cognitive impairment could also be examined. Enhanced understanding of neurobiological underpinnings may inform the selection of therapeutic targets as well as the development and selection of treatments (20). Additional research may examine conditions associated with worsened neuropsychological impairment among those with hoarding disorder and whether treatments improve neuropsychological abnormalities.

Hoarding as well as hoarding symptoms showed heritability ranging from 45% to 71%, just below that of OCD (74% with a confidence interval of 60%–83%) (53–57). In a community-based pediatric sample, study findings indicated that the L_G+S variant of 5‐HTTLPR was significantly associated with hoarding in men, whereas a trend was shown for variation downstream of HTR1B to be linked with hoarding in women (6). Associations were evidenced between T-allele carriers and hoarding (58) as well Val-allele carriers and hoarding (59). Perroud and colleagues (60) conducted a genome-side association study with White twins (N=3,410) and found no genome-wide significance; however, two genomic loci on chromosome 5 and 6 showed suggestive evidence for association with hoarding traits. There also appears to be a link between hoarding traits and the glutamatergic system, although further investigation of this relationship is needed (61).

Research suggests that genetic factors may contribute to the comorbidity of hoarding disorder with other psychiatric conditions. Specifically, Zilhão et al. (62) found that genetic factors explained 50.4% and 70.1% of the covariance between hoarding disorder and OCD symptoms and Tourette’s disorder, respectively. Specific variations in genes were also significantly correlated between hoarding disorder and OCD symptoms (0.41) and Tourette’s disorder (0.35), suggesting a common genetic basis to these conditions. Current research on the genetics of hoarding disorder is limited, and extensive further study is needed on genetic risk factors and unique genetic signatures of hoarding disorder and other obsessive-compulsive related disorders (61).

Attachment and Identity

Since our 2015 article (63), updated research has expanded on the role of attachment and identity issues regarding hoarding etiology. Attachment theory posits that infants form significant bonds to early attachment figures (e.g., their parents) and seek to maintain these attachments that offer protection, safety, and comfort (64). However, when attachment figures are repeatedly unavailable, individuals may, in turn, develop insecure attachment styles lasting into adulthood. Adult insecure attachment can manifest as either attachment anxiety (i.e., fear of abandonment) or attachment avoidance (i.e., fear of intimacy). Individuals diagnosed as having hoarding disorder have been found to experience both greater attachment anxiety and attachment avoidance compared with nonclinical samples (64). For those with attachment anxiety, object attachment has been suggested to act as a substitute for interpersonal relationships because relationships with inanimate objects may be perceived as less threatening than with people (64). Neave et al. (65) found that attachment anxiety and object attachment were both significant predictors of hoarding symptoms. Noberg et al. (66) further reported that increased attachment anxiety was correlated with greater distress intolerance and a stronger tendency to anthropomorphize inanimate possessions. Decreased tolerance to distress has, in turn, been linked to increased avoidance behaviors (67), which may manifest among individuals with hoarding disorder as avoidance of discarding and sorting items, cleaning, or even thinking about the clutter (18).

There is preliminary empirical evidence of a link between clinical hoarding and self-identity (12, 68). Kings et al. (12) described case reports of people with hoarding behavior who formed strong emotional attachments with possessions that they associated with the identities of others (e.g., a deceased spouse). These possessions could similarly be associated with the person’s perception of individuality (i.e., objects becoming symbols of their personal passions and interests) (12). Chou et al. (68) found that aspects of compromised self-identity (e.g., self-criticism and shame) were positively correlated with hoarding symptoms and beliefs. There have also been findings demonstrating a positive association between compulsive buying and a poorly defined sense of identity (69). These varied findings, although preliminary, suggest that acquired possessions can become integrated with the concept of self-identity among people who hoard.

Cognitive and Behavioral

The cognitive-behavioral model of hoarding (24) suggests that the primary symptoms of hoarding (i.e., saving, clutter, and acquiring) are caused by certain vulnerabilities (e.g., early life attachment difficulties), information processing problems, thoughts and beliefs about possessions, and positive and negative emotions. There are now several studies that verify the concepts highlighted in the cognitive-behavioral model. These elements include increased emotional reactivity (70), intolerance of uncertainty (71), anxiety sensitivity (72) and impulsivity (73), greater level of worry concerning the potentially catastrophic consequences of forgetting (74), and differences in planning and problem solving among people with hoarding disorder compared with control groups (74). Other factors have only recently been proposed as relevant to the onset and progression of hoarding disorder; these factors include object‐affect fusion (75) and the involvement of self (12, 76).

Insight and Motivation

Many individuals who hoard lack sufficient insight to recognize the extent of their clutter and the negative consequences associated with this accumulation (77). Some studies have used external observer ratings of hoarding severity to measure insight. In a web-based survey, family members of people who hoard reported significantly higher severity ratings compared with their estimates of how they thought the affected person would rate their own symptoms (77). Decreased insight can result in increased health and safety risks, family conflict, and involuntary involvement with mandated community agencies (26). Poor insight has been attributed to early childhood experiences of insecure attached families, resulting in limited opportunities to learn organization and decision-making skills (78). Preliminary research on the intersection of insight and hoarding suggests that insight is multidimensional, composed of decreased awareness of illness and defensiveness toward interventions forced by family or the community at large. Existing hoarding treatment research has similarly suggested a lack of motivation to correct the problem (79). Accordingly, individuals with poor or absent insight do not generally seek help for their behavior and may in fact resist uninvited intervention efforts (80).

Interventions

Cognitive-Behavioral Therapy (CBT)

CBT is manualized (15), has been extensively tested (81), and is presently considered the standard evidence-based treatment for hoarding disorder (2). CBT is a time-intensive weekly therapy that aims to modify emotions, cognitions, and behaviors related to hoarding (2, 82). CBT for hoarding provided on an individual basis often includes components of decision-making training, sorting and discarding exercises, organization training, exposure to nonacquiring cognitive restructuring, and motivational interviewing (15). Regular home visits are strongly recommended and have been applied in most outcome studies. CBT has been found to be particularly effective at addressing difficulty discarding, reducing clutter volume, and decreasing acquiring behaviors (2, 81). CBT primarily has an intrapersonal focus and, therefore, does not necessarily include interventions such as assisting with home cleanup. Accordingly, this treatment also does not specifically target the social consequences of hoarding, such as affected family relations and community-based risks. Finally, because few mental health providers have the expertise required to provide hoarding-specific CBT, the widespread availability of this treatment is limited (2).

Initially modeled on individual CBT practices, protocols for group-based CBT for hoarding have also been developed and tested. Group CBT is similarly composed of multiweek sessions that provide education about hoarding, decision-making training, organization exercises, and cognitive restructuring in which patients are asked to evaluate their hoarding-related beliefs and are encouraged to take alternative nonhoarding perspectives (83). Interest in group CBT over individual CBT can be attributed to the general advantages of group-based therapies, including greater social interaction and involvement as well as expected higher cost-efficiency (83). Bodryzlova et al.’s (83) meta-analysis found that group CBT resulted in clinically significant improvements (21%–68% across treatment groups) on the severity of cluttering, acquisition, and difficulty discarding.

Peer-facilitated CBT for hoarding is an alternative group treatment that has been found to be as effective as psychologist-led group CBT (84). The Buried in Treasures workshop is the predominant manualized, peer-facilitated CBT, composed of 15 structured sessions that provide psychoeducation regarding hoarding disorder, motivation enhancement, cognitive restructuring, and discarding exercises (85). Recent additions to the Buried in Treasures treatment have been made in the form of adding in-home decluttering sessions in the final weeks of the workshop. Linkosvki et al. (85) found that the addition of these personalized sessions resulted in reductions in hoarding symptoms, clutter, and impairment of daily activities.

Virtual and Blended Therapies

Since our 2015 article (63), there has been increasing research into technology-supported interventions for hoarding (86). Such interventions include benefits such as extending access to trained practitioners; flexibility in implementation, content, and personalization; greater ease in scheduling; support and feedback between sessions; and enhanced cost-effectiveness. Several studies have examined the feasibility, acceptability, and effectiveness of integrating empirically supported CBT interventions with web-based self-help (87), individual and group videoconferencing (86, 88, 89), and “blended” face-to-face with web-based therapist assistance (90, 91). These studies show numerous benefits in addition to hoarding symptom improvement that include greater treatment completion rates, shorter duration to complete treatments, as well as strong therapeutic alliance and satisfaction ratings.

There is also increasing interest in the use of virtual reality (VR) to treat hoarding disorder, although research is limited in this area to date. VR has been shown to be effective in the treatment of related disorders such as social phobia, OCD, and generalized anxiety disorder (92). VR may be particularly beneficial for individuals who have difficulty using mental imagery techniques to visualize everyday settings (such as people with hoarding disorder), and it may serve as an alternative to home visits (92). A preliminary study (92) of VR and inference-based therapy in a group format found a significant difference in the posttreatment level of bedroom clutter in the experimental group compared with the control group. Another study that used VR to simulate participants’ home environments without existing clutter found that participants reported higher confidence and motivation to engage in behavior change postimmersion (93). As technology-based innovations continue to develop and evolve, future studies may more rigorously test web-based and VR interventions for hoarding as well as incorporate other innovations, including deep learning (94), smartphone applications, and conversational agents (86).

Compassion-Focused Therapy (CFT)

CFT has recently been identified as an alternative psychotherapeutic treatment for hoarding disorder. CFT uses a variety of interventions to stimulate self-compassion, shift blame away from oneself, and regulate negative emotions that may arise in response to cognitive-restructuring attempts (67). Mindfulness training is commonly provided as part of CFT to facilitate emotional self-awareness. Multiple studies have found that incorporating CFT techniques into standard CBT programs has resulted in greater treatment effects than those produced by CBT alone for a variety of mental illnesses, including eating disorders, posttraumatic stress disorder, major depressive disorder, personality disorders, and psychotic disorders (67). Chou et al. (67) found that the provision of CFT to individuals with hoarding disorder who remained symptomatic after initially receiving CBT resulted in satisfactory treatment feasibility and acceptability among participants. Of the participants who completed the treatment, 77% had severity scores below the cutoff for clinically significant hoarding, and 62% of participants achieved a clinically significant reduction in symptom severity. However, CFT had limited effects in addressing memory concerns and attachment-related issues as well as reducing hoarding-related beliefs.

Coordinated Community Interventions

Severe hoarding behavior commonly results in diverse public health and safety concerns, which in turn, necessitate interventions, resources, and professional expertise from a wide range of sectors, including fire prevention, sanitation, housing, protective services, legal services, health, and mental health (11). As such, many cities across North America have begun to develop coordinated, community-level responses to hoarding cases in the form of task forces, coalitions, and community networks (80). The goals of community-based, coordinated initiatives typically include decreasing the incidence of severe hoarding, increasing the physical and mental health of individuals who hoard, and preserving housing (26).

Case management is an approach that has been commonly used as part of these interdisciplinary efforts. It broadly consists of three interrelated activities: identification of clients, service coordination, and service utilization (11). Within these broad categories, specific activities can include case finding, assessment, goal setting, service planning, supportive counseling, implementation of service plans, monitoring, and evaluation. These case-management activities are typically used to provide comprehensive social services to vulnerable and marginalized populations and have been found to be well-suited to the complex needs of people who hoard (11).

Harm Reduction

On the surface, hoarding may appear to be a relatively straightforward problem to address. One could simply hire a service to completely clean out the home or forcefully relocate the person who hoards to another residence. However, existing literature describes involuntary cleanouts as both traumatic to the person who hoards and ineffective in the long run, because they often lead to increased rates of recidivism (80). As such, community-based responders are increasingly avoiding the use of these more extreme options in favor of framing their service provision through a harm-reduction approach (80). In harm reduction, the goal is not to eliminate the hoarding behavior itself but rather to decrease or mitigate the risks associated with the behavior (95). The use of this approach necessitates engagement of the person who hoards in decision-making processes and the development of a supportive and nonjudgmental client-provider relationship. Hoarding response teams that utilize a harm-reduction approach may assist the person who hoards to reduce clutter volume to preserve housing, or even reconfigure possessions into safer configurations, rather than removing them altogether (80).

Medication

As discussed in our 2015 article (63), although research on the biology and neurophysiology of hoarding suggests a variety of treatment avenues, the present literature on medications has focused primarily on serotonin reuptake inhibitors (SRIs) because of their utility for OCD, with which hoarding disorder was initially conceptualized as a subtype. Some studies on pharmacotherapy for OCD retrospectively examined patients with OCD and hoarding symptoms and found that hoarding was linked to a poorer response to SRI medication (96); however, others found that hoarding did not have a significant effect on response to pharmacotherapy among those with OCD (e.g., 97, 98). These studies focused specifically on those with OCD and did not include those with hoarding disorder without other OCD symptoms. Given that the majority (>80%) of those with hoarding disorder do not have comorbid OCD (4), it is essential that studies on medication treatment include the broader population of those with hoarding disorder.

In a prospective study, patients with hoarding (N=32) and those with OCD without hoarding (N=47) received 12 weeks of the SRI paroxetine (41.6±12.8 mg/day), with similar proportions of patients in each group being identified as full responders (hoarding disorder, 27%; OCD without hoarding, 32%) and as partial responders (hoarding disorder, 22%; OCD without hoarding, 15%) (99). Completers demonstrated a 31% mean symptom improvement on the UCLA Hoarding Severity Scale (UHSS; 24% for the entire sample) (18); thus, treatment response was similar between the two groups, although most had difficulty tolerating 40 mg of paroxetine, and few reached the target dose. To test a medication that was better tolerated, 24 patients meeting DSM-5 criteria for hoarding disorder received venlafaxine extended release (37.5-mg increments to 225 mg/day) for 12 weeks. Venlafaxine was well tolerated; symptoms improved by a mean of 36% on the UHSS and 32% on the Saving Inventory-Revised (SI-R) (21–23). Of the patients, 70% responded, and hoarding symptoms improved across difficulty discarding, excessive acquisition, clutter, and functioning (18). However, the effectiveness of serotonergic drugs for treating hoarding disorder remains largely controversial because other studies involving patients with OCD and hoarding symptoms have shown no response to this category of drugs (100, 101).

Pharmacological interventions for hoarding disorder have targeted specific hoarding symptoms that maintain disability. For example, a 12-week open trial of 40–80 mg/day (mean of 62.72) of atomoxetine (a drug used for treatment of attention-deficit hyperactivity disorder [ADHD]) resulted in a 41.3% decrease of hoarding severity using the UHSS (39.9% decrease on the SI-R) among participants with hoarding disorder who exhibited inattention and impulsivity symptoms, which have been hypothesized to underlie hoarding behaviors (100). The patients’ inattentive and impulsivity symptoms showed a mean reduction of 18.5%, which correlated with a reduction in their global functional disability. Of the 12 study participants, six were identified as full responders (average reduction of hoarding symptoms was 57.2%), and three were identified as partial responders (average reduction of hoarding symptoms was 27.3%) using the UHSS. In a small open-label study, four individuals with hoarding disorder without comorbid ADHD were treated with the stimulant methylphenidate extended release. Following 4 weeks of treatment receiving an average of 50 mg of methylphenidate extended release, three of the four participants self-reported ≥50% improvement regarding inattention on the ADHD Symptom Scale. Modest improvements in hoarding symptoms were reported by two participants, with 25% and 32% reductions on the SI-R (21–23), especially on the excessive acquisition subscale (102).

A recent review of the use of second-generation antipsychotics, such as quetiapine and risperidone, for treating hoarding disorder found no evidence to suggest that they are beneficial to patients with hoarding disorder (103). One randomized, double-blind, cross-over study examined augmenting selective serotonin reuptake inhibitors (SSRIs) with the opioid antagonist naltrexone among outpatients with OCD who were not responsive to SSRIs or clomipramine for a couple of months; however, their OCD symptoms did not improve (104). A case study of an individual with hoarding symptoms and bipolar II disorder was not responsive to elevated doses of SRIs and second-generation antipsychotics but was responsive to lamotrigine combined with methylphenidate (105).

Overall, studies on pharmacotherapy for hoarding disorder remain limited by small sample sizes, designs including open labels, medications in varying classes, predominance of patients with OCD with hoarding symptoms versus a primary hoarding disorder diagnosis, preponderance of participants in midlife, use of measures not specific or validated for hoarding, and little to no replication (100, 106, 107). An outstanding question is the potential value of adding medications to cognitive and behavioral treatments for hoarding. In their meta-analysis, Tolin et al. (81) reported a significant positive predictive effect of medication for improvement in difficulty discarding but not for overall hoarding severity or other symptoms of hoarding. However, the type of medications varied within and across studies, so the possible augmenting effects of specific medications are not yet clear. Additional research is needed to determine the efficacy of medications for hoarding disorder, alone and in combination.

Special Populations

Children and Adolescents

There remains limited literature on pediatric presentations of hoarding, with the bulk of existing knowledge being borrowed from studies of children with OCD diagnoses (108). The prevalence of hoarding disorder among adolescents has been estimated at 2% of the adolescent population (101, 108). Hoarding symptoms tend to be milder in childhood and increase in severity with age, with symptoms first presenting at an average age of 16.7 (7, 101, 108). Severity of hoarding symptoms tended to worsen over time. Children rarely accumulate clutter at the same levels of adult hoarding because their parents and other adult figures (e.g., teachers) can exert control over the child’s ability to acquire possessions (101, 109). Children who hoard typically collect seemingly useless items (e.g., candy wrappers and old school papers). This behavior tends to be accompanied by excessive concern about the location, care, and condition of the objects. Objects are also often personalized, becoming part of the child’s personal identity (110), resulting in discarding attempts becoming potentially traumatic. Hoarding symptoms among children and adolescents are associated with poor insight, indecision, inattention, poor memory, impaired problem solving and planning, increased avoidance, and comorbid conditions (e.g., Tourette’s disorder and ADHD) (101, 109). Youths with OCD and hoarding symptoms have been found to have more severe current and lifetime trajectories of OCD than those without (108).

Most standardized assessments for adults who hoard have not been normed for use with children. The only exception is the Child Saving Inventory (based on the SI-R), a 23-item scale rated by parents or caregivers on four subscales: discarding, clutter, acquisition, and distress-impairment (111). With regard to treatment for this population, the effectiveness of hoarding-modified CBT for the adult population has not been widely documented in younger samples (101). There is also limited literature on pharmacological treatment for pediatric hoarding.

Older Adults

It is estimated that the rate of hoarding among older adults is three times greater than that of the general population (2%–6%) (23). As previously detailed, hoarding symptoms tend to increase in severity with age. Hoarding behaviors present unique challenges for this population because accumulation of clutter can result in increased risks for fire danger, fall hazards, medication mismanagement, inadequate nutrition, social isolation, impairment in activities of daily living, and overall decreased quality of life (23, 31). Sixty-four percent of older adults with hoarding disorder have trouble completing self-care activities, and 81% have risks to general health because of fires, falls, and poor sanitation (23).

Cognitive impairment, such as difficulty with planning, problem solving, and memory, is often evident among older adults who hoard, further complicating both assessment and treatment efforts. Assessment instruments designed for adults who hoard are generally suitable for assessing hoarding among older adults, unless marked cognitive decline invalidates self-report measures. Given the potential inaccuracies with self-report, is it recommended that a comprehensive assessment also include home visits, reports from social supports, neurocognitive assessment, and evaluation of functional impairment and comorbid psychiatric conditions (112). Cognitive impairment has been found to result in poorer responses to CBT in other geriatric psychiatric populations (23). Thus far, cognitive rehabilitation and exposure-sorting therapy, which pairs cognitive training with behavioral exposure, has shown promise for older adults, resulting in clinically significant improvement in hoarding severity (23). Other common interventions include clutter reduction and harm-reduction strategies.

Nonvoluntary Clients

Since our 2015 article (63), research remains limited on nonconsensual clients who hoard in community settings. However, new research suggests that most individuals with hoarding behaviors do not voluntarily seek assistance without family or community pressure (113), with problems recognized during routine building or fire inspections (80). Individuals’ poor insight often results in a lack of awareness about the implications of their accumulated possessions and rejecting offers of help. Emotional attachment to their belongings may be difficult to overcome, and fear of stigma and societal judgment lead to further social isolation and avoidance of the issue.

Nonvoluntary clients’ poor insight and inconsistent motivation add to the challenge of engaging these individuals in hoarding interventions. These tendencies commonly manifest in procrastination, unresponsiveness to contact attempts by service providers, and cancelled or missed appointments (80). Some clients may withdraw consent to provider engagement despite initially agreeing to services (80). In situations in which this ongoing avoidance results in elevated safety concerns or risk of housing loss, service providers may then be required to apply legal sanctions to force compliance (80, 113).

Family

As discussed in our 2015 article (63), family members who live with a person who hoards are exposed to the same health and safety risks. Children of people who hoard are faced with constant disruptions, including loss of functional living space, unsanitary home conditions, social isolation, financial distress, and hostile family dynamics (114, 115). The effects of these challenges can have a lifetime impact on children, with the associated psychological distress lasting into adulthood. Recent research indicates that adult children of people who hoard have reported feelings of grief related to the loss of their relationship with their parent, as well as anger stemming from beliefs that their parent who hoards chose possessions over their children (115). As their parents age, adult children of people who hoard experience additional responsibilities as caregivers.

The level of caregiver burden experienced by the relatives of people who hoard has been found to be comparable with or greater than that reported by family members of people with dementia (16). Older adults who hoard require greater assistance to complete basic activities of daily living that otherwise would be neglected, a responsibility that often falls on their adult children and other relatives (16). Relatives of people who hoard also report increased levels of frustration, hopelessness, and distress in response to the hoarding person’s lack of insight, treatment ambivalence, and risk of injury from unsafe living conditions (16, 114, 115). Feelings of shame and embarrassment interfere with family members’ ability to have people visit the home, resulting in risk of social isolation (115). The negative emotions experienced by family members of people who hoard often culminate in outright rejection of the person who hoards (114, 115).

Manualized training programs have also been designed for family members of people who hoard and include components of psychoeducation on hoarding, harm-reduction techniques, communication training, and self-care (114). One such program is the Family-As-Motivators training, which was conducted in a pilot study over 14 sessions. At pre-, mid-, and posttraining measures, Family-As-Motivators resulted in improved use of coping strategies, decreased feelings of hopelessness, and decrease in self-blame (114). Another example includes family-focused, harm-reduction programming (i.e., Community Reinforcement and Family Training) (95), which focuses on improving stressed familial relationships while also encouraging the person who hoards to accept help to manage the hoarding problem. The harm-reduction approach includes five key components: enhance willingness to engage in the harm-reduction approach, assess the potential for harm, build and facilitate a harm-reduction team, plan the harm-reduction approach, and implement and manage the plan.

Conclusions

Frost and Hartl’s (1) seminal article inspired 25 years (and counting) of empirical study of hoarding. To date, research has focused on identifying specific symptoms and components of hoarding, distinguishing hoarding from OCD, and examining hoarding as a distinct DSM-5 disorder (3). This inquiry has led to the development of models for understanding hoarding disorder that focus on personal and family vulnerability factors (e.g., family history, comorbidity), information processing challenges (e.g., inattention, categorization, memory), cognitions (e.g., meaning of possessions), positive and negative emotions, biological features, and so forth. Recent investigations of cognitive processing, neurobiological correlates, and genetic aspects of hoarding are advancing the understanding of key elements of hoarding (e.g., discarding, excessive acquiring, clutter) and relevant substrates. More recent neurobiological and genetic studies further illustrate the similarities and distinctions between OCD and hoarding as well as other obsessive-compulsive and related disorders. Future research is needed to examine cognitive and affective decision making as well as cognitive impairments associated with hoarding. Additional studies are also needed to understand impairments associated with hoarding and comorbid conditions. Further study of neurobiological underpinnings of hoarding disorder may enhance the identification and selection of treatment targets and inform treatment development and the personalization of treatments. More extensive research is also needed on genetic factors and hoarding traits, including the genetic signature of hoarding disorder.

Cognitive and behavioral treatment for hoarding delivered individually and in groups have been empirically supported and considered standard care on the basis of the level of benefit at the current stage of research (81). Technology-supported hoarding interventions show promise, extending access to these evidence-based treatments, trained providers, and peer-support as well as presenting opportunities to further examine key components of hoarding (86). Additional models have been associated with substantial hoarding symptom improvement, including cognitive rehabilitation treatment for older adults (23), CFT (67), motivational enhancement, and harm reduction (114, 116). Few pharmacotherapy trials for hoarding disorder have been conducted, and existing medication studies are limited. Future studies that specifically examine participants diagnosed as having hoarding disorder need larger samples sizes that include older adults as well as more robust methodology and replication; designs should also include combining CBT and pharmacotherapy.

Current hoarding models and assessments have mainly focused on adults. Future studies are needed to develop CBT models, hoarding assessments, and interventions for youths (117). Future studies on hoarding also necessitate more inclusive samples regarding race-ethnicity and further development of assessments that are culturally and linguistically relevant. Because hoarding disorder is a multifaceted problem that spans mental and public health, a multipronged approach may be especially relevant and effective. Although much progress has been made over the past 2 decades, numerous questions still exist regarding the nature of, and optimal interventions for, hoarding disorder; thus, opportunities for many new discoveries, advances, and innovations are ahead.