Key Facts

OCD is a chronic neuropsychiatric disorder characterised by obsessions and compulsions that are time-consuming, distressing, and functionally impairing. It is one of the most disabling psychiatric conditions.

Epidemiology

Lifetime prevalence is 2-3%. Equal sex distribution overall, but males have earlier onset. Mean age of onset is 19-20 years (bimodal: childhood peak ~10 years, adult peak ~21 years). Average delay to treatment is 7-10 years. OCD accounts for significant disability — ranked by WHO as one of the top 10 most disabling conditions.

Aetiology

• Genetic: Heritability ~40-50%; first-degree relatives have 4× increased risk
• Neuroanatomical: Cortico-striato-thalamo-cortical (CSTC) circuit dysfunction — orbitofrontal cortex and caudate nucleus hyperactivity
• Serotonergic: Serotonin dysfunction — basis for SSRI treatment
• Autoimmune: PANDAS (Paediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections) — abrupt OCD onset post-streptococcal infection in children
• Psychological: Inflated responsibility beliefs, thought-action fusion, intolerance of uncertainty

Pathophysiology

• CSTC circuit model: Overactivity in orbitofrontal cortex → excessive error signalling → "something is wrong" feeling → compulsive behaviour to reduce anxiety
• Serotonin hypothesis: Supported by selective response to serotonergic drugs (SSRIs, clomipramine) but not noradrenergic drugs
• Glutamate dysfunction: Emerging evidence — riluzole and memantine under investigation
• ERP mechanism: Habituation — repeated exposure to anxiety-provoking stimuli without performing compulsion leads to anxiety reduction over time

Common Obsession Themes

• Contamination: Fear of germs, dirt, bodily fluids → washing/cleaning compulsions
• Harm: Fear of causing harm to self or others → checking compulsions
• Symmetry/ordering: Need for things to be "just right" → arranging, counting
• Forbidden thoughts: Intrusive sexual, religious, or aggressive thoughts → mental rituals, reassurance-seeking

Common Compulsion Types

• Washing and cleaning
• Checking (locks, appliances, safety)
• Counting, ordering, arranging
• Mental rituals (praying, repeating words)
• Reassurance-seeking
• Hoarding (may overlap with hoarding disorder)

Key Clinical Features

• Patient recognises thoughts are their own (not inserted) and usually recognises they are excessive/irrational
• Attempts to resist compulsions cause mounting anxiety
• Symptoms are time-consuming (>1 hour/day) and cause significant distress or functional impairment

Red Flags

• Severe OCD with total functional impairment — consider specialist inpatient OCD unit
• OCD with psychotic features — poor insight subtype, consider antipsychotic augmentation
• Sudden onset OCD in child post-streptococcal infection — PANDAS, consider paediatric referral
• Suicidal ideation — comprehensive risk assessment

Bedside

• Y-BOCS: Gold standard severity rating (0-40); mild <16, moderate 16-23, severe 24-31, extreme 32-40
• OCI-R (Obsessive-Compulsive Inventory-Revised): Self-report screening tool
• PHQ-9/GAD-7: Screen for comorbid depression and anxiety
• Risk assessment: Suicidal ideation, self-harm

Bloods

• TFTs: Exclude thyroid dysfunction
• FBC: Baseline if starting clomipramine
• ASOT/anti-DNase B: If PANDAS suspected in children

Special Tests

• ECG: Before clomipramine (cardiotoxic); baseline for SSRIs at high doses
• Neuropsychological testing: If cognitive concerns or diagnostic uncertainty
• Neuroimaging: Not routine — research shows OFC and caudate hyperactivity on fMRI

Non-pharmacological

• Mild OCD: Low-intensity CBT (guided self-help with ERP)
• Moderate-severe OCD: High-intensity CBT with ERP (specialist therapist, 12-20 sessions)
• ERP protocol: Graded exposure to feared stimuli + prevention of compulsive response → habituation
• Family involvement: Psychoeducation, reducing accommodation of compulsions

Pharmacological (NICE CG31)

• First-line SSRI (higher doses than for depression):
  • Fluoxetine 60-80mg OD
  • Sertraline 200mg OD
  • Fluvoxamine 100-300mg OD
  • Paroxetine 40-60mg OD
• Allow 8-12 weeks at adequate dose before concluding ineffective (longer than depression)
• Second-line: Clomipramine 75-250mg OD (most effective single agent, but anticholinergic/cardiac side effects)
• Augmentation (specialist): Low-dose antipsychotic (risperidone 0.25-2mg, aripiprazole 5-15mg) added to SSRI
• Treatment duration: Continue for ≥12 months after remission; gradual tapering

Referral Criteria

• Moderate-severe OCD — secondary care for CBT with ERP and SSRI optimisation
• Treatment-resistant OCD (failed 2 SSRI trials + CBT) — specialist OCD service
• Severe functional impairment — specialist/inpatient OCD unit
• PANDAS — paediatric neurology/psychiatry

• CBT with ERP: 60-70% response rate; gains well-maintained with continued practice
• SSRIs: 40-60% response rate; high relapse rate on discontinuation (~50%)
• Combined CBT + SSRI: Best outcomes, especially for moderate-severe OCD
• Course: Chronic and relapsing in most cases; ~20% have a chronic unremitting course
• Predictors of poor outcome: Early onset, poor insight, hoarding symptoms, comorbid depression, family history
• Functional recovery: Even with symptom reduction, many patients have residual functional impairment

Y-BOCS Severity

NICE CG31 Stepped Care