OCD and Related Disorders — OCD, Trichotillomania, Body Dysmorphic Disorder and Hoarding

Obsessive-compulsive disorder (OCD) is a disabling condition affecting roughly 1% to 3% of people during their lifetime. It is characterised by obsessions — intrusive, repetitive thoughts, urges or images that are hard to control — and compulsions — repetitive actions or mental acts the person feels driven to perform. Both consume a lot of time and cause marked distress and impairment.

The key psychological feature is that the obsessions are ego-dystonic: most adults find them distressing and recognise that their compulsive behaviour is excessive. This preserved insight is what separates OCD from psychosis in an exam vignette. Children often struggle to describe their obsessions.

OCD has moved around the classification systems. DSM-III grouped it with phobias, DSM-IV placed it under anxiety disorders, and DSM-5 gave it its own chapter — obsessive-compulsive and related disorders — which is how the exam now expects you to classify it.

DSM-5 lists the following members of the group. Apart from OCD, the ones examiners test most are body dysmorphic disorder, hoarding disorder, trichotillomania and excoriation (skin-picking) disorder.

The diagnosis is clinical. Either obsessions or compulsions (or both) must be present, and the behaviours must be time-consuming — one hour or more per day — or cause clinically significant distress or impairment.

• The symptoms are not due to a substance, a medication or another medical condition.
• They are not better explained by another mental disorder — this is why the differential matters (see below).
• Obsessions and compulsions can, in theory, occur independently of each other, although most patients have both.

Clinicians group the symptoms into dimensions. Exam stems usually describe one dimension and ask for the diagnosis or the best treatment.

On the mental status examination the patient is usually well groomed but visibly anxious, may be seen washing, tapping or checking, and has linear thought process, no hallucinations, intact cognition and preserved insight — they know the thoughts are irrational but feel powerless to resist. Postpartum OCD often presents as intrusive thoughts of harming the baby; mothers may hide them for fear of judgement, so the clinician must ask sensitively and assess safety.

OCD arises from an interplay of genetic and environmental factors. Twin studies estimate heritability at about 48%, falling to 35% once maternal effects are accounted for, but no reproducible genetic marker has been found.

• Circuit model: OCD is increasingly viewed as a network disorder involving the cortico-striato-thalamo-cortical (CSTC) loop, which links the prefrontal cortex with the striatum and thalamus. The loop has a direct pathway (initiates behaviour) and an indirect pathway (inhibits or modulates it); in OCD the balance is disturbed.
• Serotonin: the response to clomipramine, a strong serotonin reuptake inhibitor, pointed to serotonin, but buspirone and ondansetron do not work, so the model is incomplete. Glutamate is an emerging target (riluzole has shown preliminary benefit).
• Basal ganglia lesions: some cases follow Sydenham's chorea or ischaemic events affecting the globus pallidus and caudate.
• PANDAS / PANS: paediatric autoimmune neuropsychiatric disorders associated with streptococcal infection. Unlike usual OCD the onset is sudden and severe, with extras such as handwriting deterioration and emotional lability.
• Cognitive-behavioural model: maladaptive beliefs (inflated responsibility, overvaluing thoughts, perfectionism, intolerance of uncertainty) drive anxiety, and rituals reduce it — which reinforces them.

• Lifetime prevalence 1% to 3%; usually a chronic course with early onset.
• Commonest age band 18 to 29 years. Nearly a quarter of males have symptoms before age 10; in females it usually emerges in adolescence. The peripartum and postpartum phases carry an increased risk.
• About 90% meet criteria for at least one other psychiatric disorder — anxiety, mood, impulse-control and substance use disorders are the commonest.
• OCD is frequently under-diagnosed and under-treated.

The most widely accepted rating tool is the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), scored 0 to 40, where 40 is the most severe. The clinician rates five items for obsessions and five for compulsions: time occupied, interference, distress, resistance and degree of control. A six-question short OCD screener with a sensitivity of 97% is also described for screening.

Treatment combines psychotherapy and drugs. Cognitive-behavioural therapy with exposure and response prevention (ERP) is the best-supported behavioural technique: the patient is exposed to the anxiety-provoking stimulus and guided to abstain from the compulsion. It is first-line, especially when it matches patient preference, trained therapists are available and there is no comorbidity that needs drugs. Home-based ERP assignments are central to success.

About half of patients do not respond to first-line treatment. Poor-response predictors are high severity, marked impairment, sexual, religious and hoarding symptoms, poor insight, high comorbidity and non-adherence. Combining fluoxetine with clomipramine raises blood levels of both drugs and risks seizures, arrhythmias and serotonin syndrome.

Antipsychotics are an augmentation option, not a first-line one. Related reading on other psychiatric treatments: electroconvulsive therapy.

BDD is a preoccupation with one or more perceived defects or flaws in physical appearance that are not observable, or appear slight, to others. Global prevalence is about 2% to 3%, higher in women. It sits in the obsessive-compulsive spectrum, having been called an atypical somatoform disorder before DSM-5.

• Criteria: the preoccupation, plus repetitive behaviours or mental acts in response (mirror checking, camouflaging, excessive grooming, comparing, reassurance seeking), causing significant distress or impairment, and not better explained by an eating disorder.
• Specifiers: with muscle dysmorphia (belief that the body or muscles are too small) and with panic attacks. Insight is graded as good or fair, poor, or absent/delusional.
• Cosmetic surgery: about 13% of patients in general cosmetic surgery clinics, 20% of rhinoplasty patients and 11% of orthognathic surgery patients have BDD. Surgery is not an effective solution.
• Treatment: CBT directed at BDD, plus high-dose SSRIs or clomipramine; augmentation options include buspirone, memantine or a second-generation antipsychotic.
• Safety: suicidal ideation and behaviour are common; active suicidality or a recent attempt warrants hospital admission.

Trichotillomania (hair-pulling disorder) has a lifetime prevalence as high as 3.5%, with onset in adolescence and a female predominance (about 9:1 in reported series). The diagnosis rests on five DSM criteria.

• Clues: hairs of differing lengths and regrowth stages in a geometric patch; the 'Friar Tuck' sign (crown loss with preserved temporal and occipital hair). Scalp hair is pulled most often, but any body hair can be.
• Ritual: some patients inspect the hair root and eat the hair — risk of a trichobezoar; think of it when there is pain, nausea, vomiting or constipation.
• Biopsy (not required) shows a non-inflammatory, non-scarring alopecia with traumatic follicular damage and trichomalacia; the follicle count is normal.
• Treatment: habit reversal training (awareness, a competing response and social support) is the core therapy. SSRIs have modest, inconsistent benefit; clomipramine has more support; N-acetylcysteine has only case reports.

Excoriation disorder is the skin-picking counterpart: recurrent picking leading to skin lesions despite attempts to stop. It sits next to trichotillomania in DSM-5 and responds to the same behavioural approach.

Kleptomania is classed under the disruptive, impulse-control and conduct disorders in DSM-5, alongside pyromania, intermittent explosive disorder, ODD and conduct disorder. It is defined as recurrent urges to steal objects not needed for personal use or for their monetary value, with heightened tension before the theft and relief afterwards; the stealing does not occur during a hallucination, delusion, mania or conduct disorder. Lifetime prevalence is about 0.6%, and it is the one impulse-control disorder that is commoner in females (about 3:1). Do not label it OCD: a compulsion neutralises an obsession, whereas kleptomania is an urge-driven act with tension-relief.

For the related somatic and dissociative categories, see dissociative and somatic symptom disorders. For the legal framework around treating psychiatric patients, see the Mental Healthcare Act 2017.

• A vignette of hand washing or checking with preserved insight → OCD; treatment ERP plus SSRI.
• A patient with bald patches of mixed hair length and a habit of pulling → trichotillomania; therapy habit reversal.
• A person convinced their nose is deformed who keeps seeking surgery → body dysmorphic disorder; surgery does not help; give SSRI plus CBT.
• Sudden-onset OCD with tics after sore throat in a child → PANDAS.
• 'Which scale?' → Y-BOCS. 'Which circuit?' → CSTC loop. 'Which chapter in DSM-5?' → Obsessive-compulsive and related disorders.