Obsessive-Compulsive Disorder

Introduction

Obsessive-compulsive disorder (OCD) is characterised by recurrent obsessions, compulsions, or both, that are time-consuming or cause marked distress or significant impairment in daily functioning.¹ It typically presents in adolescence or early adulthood, though onset in childhood is well recognised, and affects around 1-2% of the population.

OCD is frequently misunderstood as a preference for tidiness. The reality is a distressing and disabling condition in which unwanted thoughts intrude despite the person's efforts to resist them, and compulsive rituals - far from being pleasurable - are performed reluctantly to relieve mounting anxiety. Recognising the ego-dystonic nature of the symptoms (the person finds the thoughts alien and unwanted, not something they want or endorse) is central to both diagnosis and to distinguishing OCD from psychosis.

Onset is often gradual, and there is frequently a substantial delay - historically many years - between symptom onset and diagnosis, driven by shame and secrecy about the content of obsessions, particularly those involving violence, sex or contamination.

Aetiology

OCD has a stronger genetic and neurobiological basis than most anxiety disorders, alongside a well-characterised cognitive-behavioural maintaining cycle.

• Genetics: heritability of around 40-50%; higher concordance in monozygotic than dizygotic twins, and a higher rate in first-degree relatives
• Neurobiology: dysfunction in the cortico-striato-thalamo-cortical circuit, particularly the orbitofrontal cortex, anterior cingulate and caudate nucleus, which mediates error-detection and repetitive checking behaviour
• Serotonergic dysfunction: supported indirectly by the specific efficacy of serotonergic (but not purely noradrenergic) antidepressants
• PANDAS/PANS: an abrupt-onset paediatric variant proposed to follow streptococcal infection via an autoimmune mechanism - uncommon and still debated, but a recognised exam topic
• Cognitive-behavioural model: intrusive thoughts occur in everyone, but in OCD they are catastrophically misinterpreted as meaningful, dangerous, or reflecting the person's true character (thought-action fusion - believing that having a thought is as bad as acting on it). Compulsions temporarily relieve the resulting anxiety, which negatively reinforces the ritual and entrenches the cycle.
• Why it self-perpetuates: because the compulsion is always followed by relief, the brain learns that the ritual prevented the feared outcome - so the belief is never disconfirmed and the cycle strengthens with every repetition
• Personality: perfectionism and an inflated sense of responsibility for preventing harm are common premorbid traits

Risk factors

• Family history of OCD or tic disorders
• Personal or family history of tic disorder, including Tourette syndrome
• Perfectionistic or highly conscientious premorbid personality traits
• Childhood adversity or trauma
• Pregnancy and the postnatal period - a recognised time of new onset or exacerbation
• Streptococcal infection preceding abrupt paediatric onset (PANDAS), though this remains a minority and contested cause

Clinical features

Obsessions

Recurrent, persistent thoughts, images or urges that are intrusive and unwanted, cause marked anxiety or distress, and that the person attempts to ignore, suppress or neutralise with another thought or action. Crucially, the person recognises the obsessions as a product of their own mind, however unwelcome (distinguishing them from thought insertion in psychosis).

Compulsions

Repetitive behaviours (washing, checking, ordering) or mental acts (counting, praying, silently repeating a phrase) that the person feels driven to perform in response to an obsession, or according to rigid rules. They are aimed at preventing or reducing distress or a feared event, but are excessive and not realistically connected to what they are meant to neutralise, or are clearly excessive.

• Washing and cleaning - handwashing, showering or cleaning rituals, often to the point of skin damage
• Checking - repeatedly checking locks, appliances or that no harm has occurred
• Ordering and arranging - until objects feel symmetrical or 'just right'
• Mental rituals - counting, repeating words or prayers silently
• Reassurance-seeking - repeatedly asking others to confirm safety or that harm has not occurred
• Avoidance - of triggers for obsessions, which can become as disabling as the rituals themselves

Severity

The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) is the standard tool, separately scoring the time occupied, distress, resistance, and interference caused by obsessions and by compulsions, and is used both to grade severity and to track treatment response.

Mental state examination

Differential diagnosis

• Generalised anxiety disorder: worry about real-life concerns, without discrete obsessions or ritualised compulsions
• Psychotic disorder: thought insertion and delusions are held with conviction and without resistance, unlike the ego-dystonic, resisted obsessions of OCD - though OCD with poor insight can blur this distinction
• Body dysmorphic disorder: obsessional preoccupation specifically with a perceived defect in appearance
• Illness anxiety disorder: obsessional preoccupation specifically with having or developing a serious illness
• Autism spectrum disorder: repetitive behaviours and routines are usually experienced as calming or preferred, not as ego-dystonic and distressing
• Depression: ruminations are typically mood-congruent and about guilt or worthlessness, rather than the specific, often bizarre content of OCD obsessions, though the two frequently coexist
• Hoarding disorder: classified separately in ICD-11 - persistent difficulty discarding possessions, without necessarily the intrusive obsession/compulsion structure of OCD
• Tic disorders and Tourette syndrome: motor and vocal tics rather than goal-directed compulsions performed to neutralise an obsession, though the two frequently co-occur

Investigations

OCD is diagnosed clinically. There is no diagnostic test, and investigations are used only to exclude organic mimics or assess comorbidity.

• Y-BOCS to establish baseline severity and monitor treatment response³
• History of onset - abrupt paediatric onset, particularly following a sore throat, raises the possibility of PANDAS and warrants paediatric review
• Screen for comorbid depression, other anxiety disorders and tic disorders, all of which are common
• Physical examination for skin damage from excessive washing

Asking about obsessions people are ashamed of

OCD has a median delay of many years between onset and diagnosis, and shame about symptom content is the main reason. Patients with violent, sexual or blasphemous intrusive thoughts frequently believe they are dangerous, perverted or evil, and will not volunteer them - so they must be asked about directly, with explicit normalisation.

• Normalise first, then ask: 'Many people with these difficulties get unwanted thoughts that they find horrible and that go against everything they believe. Does that happen to you?'
• Name the categories explicitly, since patients often will not: thoughts about harming others including children, unwanted sexual thoughts, blasphemous thoughts, and fears of having done something terrible without remembering
• Clarify the quality - are the thoughts unwanted and distressing (obsessional), or wanted and endorsed? This distinction determines whether this is OCD or a genuine risk concern
• Ask about mental compulsions, which are invisible and frequently missed - silent counting, praying, reviewing memories to check nothing happened, mentally 'undoing' a thought
• Ask about reassurance-seeking and avoidance, which are compulsions in a less obvious form
• Quantify the time lost - hours per day is the most useful single measure of severity

Management

NICE recommends a stepped-care approach based on the degree of functional impairment.²

Exposure and response prevention (ERP)

ERP is the specific, most effective form of CBT for OCD. The person is systematically exposed to situations that trigger obsessions, while being supported to resist performing the accompanying compulsion, allowing anxiety to rise and then naturally fall (habituate) without the ritual. Repeated practice breaks the negative reinforcement cycle that maintains the disorder.

A worked example makes the mechanism clear. A patient with contamination obsessions who washes for 40 minutes after touching a door handle would work up a hierarchy - touching a clean handle, then a public one, then a bin lid - and at each step touch the object and then not wash, remaining with the anxiety until it falls of its own accord. The learning is not that the object was clean, but that the anxiety subsides without the ritual and that the feared catastrophe does not occur.

• The compulsion, not the obsession, is the treatment target - obsessions cannot be suppressed directly, and trying to do so increases them
• Include mental compulsions and reassurance-seeking in response prevention, or treatment will appear to fail while the ritual simply goes underground
• Involve the family in reducing accommodation, since a relative who continues to provide reassurance or perform the checking undermines the whole intervention
• Anxiety must be allowed to peak - a session that ends while the person is still at peak anxiety, or where they ritualise afterwards, can reinforce rather than reduce the fear

Medication

An SSRI is first-line pharmacological treatment. Clomipramine, a TCA with potent serotonergic activity, is an effective alternative, usually reserved for cases not responding to an SSRI because of its side-effect burden.

For treatment-resistant OCD, options include switching to a different SSRI or to clomipramine, augmenting an SSRI with an antipsychotic, or referral for more intensive specialist input, which may include intensive outpatient or inpatient treatment in severe, function-limiting cases. Effective medication is continued for at least 12 months after response before any attempt at withdrawal, and relapse on stopping is common, so some patients remain on long-term treatment.

Complications

OCD causes substantial functional impairment - lost time to rituals, disrupted relationships and employment, and social withdrawal driven by shame about symptom content. Comorbid depression is very common and is associated with an increased risk of suicidal ideation. Skin damage from excessive washing, and family accommodation of rituals (family members participating in or facilitating compulsions to reduce the person's distress) are both frequent and worth asking about directly, as they can maintain the disorder and need to be addressed in treatment.

Red flags

Prognosis

OCD tends to follow a chronic course if untreated, often waxing and waning in severity in relation to life stress, but the majority of patients achieve significant and durable improvement with ERP, an SSRI, or the combination. Early treatment, good engagement with ERP, and limiting family accommodation of rituals are all associated with better outcomes.

A substantial minority experience relapse, particularly if medication is stopped abruptly, so continuation treatment for at least 12 months after response is standard, with some patients requiring longer-term or indefinite treatment for a chronic, relapsing course.