Diagnostic subtyping of obsessive–compulsive disorder: Have we got it all wrong?

‘The idea of a disease entity is not an objective to be reached, but our most fruitful point of orientation’ (Jaspers, 1959).

The presenting complaint of patients with obsessive–compulsive disorder (OCD) is often their predominant OCD symptom (e.g. excessive checking, hand-washing, or distressing intrusive thoughts). Yet OCD symptoms do not feature as OCD specifiers in any of the major diagnostic classificatory systems such as the ICD-10 (World Health Organization, 1992), DSM-IV-TR (American Psychiatric Association, 1994), or even in the proposed changes for DSM-5 (American Psychiatric Association, 2012). Instead, the degree of insight and the presence of comorbid tics are preferred as specifiers, and hoarding is proposed to constitute a separate disorder in DSM-5 (American Psychiatric Association, 2012). The mounting evidence supporting the role of predominant OCD symptoms in explaining the heterogeneity of OCD (Bloch et al., 2008; Mataix-Cols et al., 2005) may lead one to wonder why they are not featured in major diagnostic classificatory systems and whether we have got it all wrong.

Symptom-based subtypes of OCD

DSM-5 may not have embraced symptom-based subtypes of OCD due to the degree of co-occurrence between the major OCD symptoms. Patients with OCD can have complex combinations of many potential OCD symptoms; for example, contamination obsessions with washing and checking compulsions. In an attempt to understand which OCD symptoms tend to co-occur more frequently, there have been over 20 large studies (Leckman et al., 2010) that have employed principal components analysis to show that all major OCD symptoms can be explained by four to five major symptom dimensions. There has also been a meta-analysis of these studies that provides further support for these symptom dimensions (Bloch et al., 2008). Almost all of these studies support a hoarding symptom dimension, a contamination/cleaning symptom dimension and a symmetry/ordering symptom dimension. The fourth and fifth symptom dimensions are either comprised of an aggressive/sexual/religious obsession dimension (unacceptable/taboo thoughts) and a checking compulsions dimension (doubt/checking) in a model with five dimensions (Williams et al., 2011) or a combination of these symptoms in a model with four symptom dimensions (Bloch et al., 2008).

Further support for the validity of OCD symptom dimensions arises from the multiple studies (Leckman et al., 2010) that associate them with distinct descriptive and clinical characteristics. The most consistent findings are summarised in Table 1.

Table 1.

Characteristics associated with five potential OCD symptom dimensions.

Hoarding	Contamination / cleaning	Symmetry / ordering	Unacceptable / taboo thoughts	Doubt / checking
– Ego-syntonic – Less insight – Greater severity – Likely to worsen with time – Poor response to treatment – Impaired decision-making – High familiality – Less activity in cingulate and orbitofrontal cortex	– Constant concern rather than an intrusive thought – Increased avoidance – Good response to ERP and SSRIs – Greater activation of the prefrontal regions and right caudate – Possibly more common in females	– Ego-syntonic – ‘Just-right’ feelings and a sense of incompleteness – Less insight – Early age of onset – Comorbidity with tics – More common in childhood – May lessen with age – Associated with perfectionism	– Ego-dystonic – Good insight – Greater association with suicidal tendencies – Early age of onset – Precipitous onset – Poorer response to ERP – Associated with a need to control one’s thoughts	– Good response to ERP – Poor memory confidence – Overestimation of threat and responsibility – Increased activation of bilateral striatal areas, putamen, globus pallidus, thalamus and dorsal cortical areas

ERP: exposure and response prevention; SSRIs: selective serotonin reuptake inhibitors.

OCD with poor insight

OCD with poor insight is currently the only diagnostic specifier for DSM-IV-TR and was included after a DSM-IV field trial recognised that up to 36% of patients with OCD did not view their symptoms as excessive or unreasonable (Foa and Kozak, 1995). In subsequent studies (Alonso et al., 2008; Eisen et al., 2004; Himle et al., 2006), poor insight has been associated with greater severity of OCD symptoms, hoarding symptoms, obsessive–compulsive personality disorder, younger age of onset, being single and a poorer response to behavioural treatment.

For DSM-5, it has been proposed that the insight specifier not only remains, but be expanded to specify whether insight is ‘good or fair’, ‘poor’ or ‘absent’. There are several problems with this approach. First, the characteristics associated with poor insight may be attributable to increased severity of symptoms. Second, insight is multidimensional and difficult to accurately assess (Brakoulias and Starcevic, 2011). Existing instruments (Eisen et al., 1998; Neziroglu et al., 1999) aim to measure a prominent belief which is not always identifiable in OCD. For example, people who count compulsively do not usually report a belief associated with their counting. Additionally, patients may view their compulsions as excessive on reflection with their clinician, but not when they are in a perceived threatening situation. Hence, insight can fluctuate. Third, the insight specifier does not provide a comprehensive explanation for the many different presentations of OCD.

Tic-related OCD

A tic-related OCD subtype has been proposed for DSM-5. This subtype could be specified if the individual has a lifetime history of chronic tic disorder (American Psychiatric Association, 2012). A lifetime history of a tic disorder occurs in 10% of adult OCD samples (Hasler et al., 2007) and up to 40% of child and adolescent OCD samples (Holzer et al., 1994). Individuals with OCD and a history of a tic disorder have greater familiality (Grados et al., 2001), earlier onset of symptoms (Grados et al., 2001), are more likely to be male (Jaisoorya et al., 2008; Leckman et al., 1994), are more likely to have symmetry/ordering symptoms (Leckman et al., 1994) and there are some studies (McDougle et al., 1994) to suggest that they are more likely to respond to antipsychotic augmentation of their antidepressant treatment.

Despite an initial enthusiasm that the increased familiality associated with tic-related OCD would reveal a genetic correlate, years of research has not yet produced such a finding (Pauls, 2008). There are significant overlapping features between tic-related OCD and other proposed subtypes, such as OCD with early onset and OCD with predominant symmetry/ordering symptoms. A differential treatment response is also in doubt as there is no evidence that tic-related OCD has a differential response to behavioural therapies (Himle et al., 2003; Storch et al., 2008) and some evidence that there may not be a differential response to antipsychotic augmentation (McDougle et al., 2000). As with OCD with poor insight, a tic-related subtype of OCD would do little to explain the wider heterogeneity of OCD.

Hoarding disorder

Perhaps the most dramatic change proposed for DSM-5 (in relation to OCD) is the introduction of a hoarding disorder that is separate from OCD, but that would be classed as an obsessive–compulsive-related disorder (American Psychiatric Association, 2012). It has been proposed that patients with hoarding symptoms that are not better accounted for by another disorder (e.g. OCD) would receive the diagnosis of hoarding disorder. Research in this area is complicated by different recruitment criteria and changing definitions. Exactly how patients with hoarding disorder will differ from patients with OCD with predominant hoarding symptoms or patients with hoarding as a symptom of another disorder (e.g. major depression) is yet to be determined.

The introduction of a hoarding disorder recognises the differences between hoarding and other OCD symptoms (see Table 1). However, other OCD symptoms are also associated with distinct characteristics and there are no calls for them to become distinct disorders. Some argue that the ego-syntonic nature of hoarding is in contrast with the core phenomenology of OCD and, whilst this is true, the degree to which obsessions are ego-dystonic varies considerably when one compares sexual obsessions (usually very ego-dystonic) to symmetry obsessions (often ego-syntonic). Epidemiological studies have supported the formation of a hoarding disorder diagnosis by showing that a very small number of people with hoarding meet criteria for OCD (Samuels et al., 2008). These studies contrast with studies of OCD samples showing that all OCD symptoms (including hoarding) co-occur with each other at high rates (Bloch et al., 2008). The proposal for a hoarding disorder again represents an attempt to understand one aspect of OCD, rather than an attempt to understand its many different presentations.

Conclusions

A piecemeal approach that identifies OCD specifiers and then their related characteristics has not been particularly beneficial in explaining the heterogeneity of OCD symptoms. Considering that OCD is characterised by many co-occurring symptoms, the most fruitful point of orientation must surely be one that tries to explain as many of the different symptoms as possible in the one model. At this point in time, it appears we may have got it all wrong and that the benefits of a dimensional symptom-based model for OCD may have been overlooked.