Obsessive-Compulsive Disorder
Psychiatry · Anxiety · lean revision notes
Obsessive-Compulsive Disorder
Obsessive-Compulsive Disorder (OCD) is a chronic, disabling anxiety-spectrum illness defined by recurrent ego-dystonic obsessions and/or compulsions that consume time and cause marked distress. It is a perennial NEET PG favourite — expect questions on the serotonin hypothesis, the Y-BOCS scale, clomipramine, high-dose SSRIs, and exposure-response prevention (ERP).
Definition & core concepts
OCD is characterised by two cardinal symptom types, one or both of which must be present:
- Obsessions — recurrent, intrusive, unwanted thoughts, images, or urges that the patient recognises as a product of their own mind (unlike thought insertion in schizophrenia) and which generate anxiety. They are ego-dystonic (alien, unacceptable to the self) and the patient attempts to resist or neutralise them.
- Compulsions — repetitive behaviours (handwashing, checking, ordering) or mental acts (counting, praying, silent repetition) that the person feels driven to perform in response to an obsession, or according to rigid rules, in order to reduce anxiety or prevent a dreaded event. The act is not realistically connected to what it is meant to prevent or is clearly excessive.
High-yield: Obsessions are ego-dystonic and resisted; this distinguishes OCD from obsessive-compulsive personality disorder (OCPD), where the perfectionistic traits are ego-syntonic and not resisted.
The classic cycle is: obsession → anxiety → compulsion → transient relief → reinforcement → recurrence of obsession. The compulsion is negatively reinforced because it temporarily relieves anxiety, which perpetuates the disorder.
Diagnostic threshold
Per DSM-5 / ICD-11, the obsessions or compulsions are time-consuming (>1 hour/day) or cause clinically significant distress/impairment. DSM-5 moved OCD out of the anxiety disorders into its own chapter — "Obsessive-Compulsive and Related Disorders."
High-yield: DSM-5 added an insight specifier — good/fair insight, poor insight, or absent insight/delusional beliefs. Most adults retain insight; poor insight predicts worse prognosis. A tic-related specifier is also recognised given the strong comorbidity.
Classification — OCD spectrum (OC-related disorders)
| Disorder | Core feature | Pearl |
|---|---|---|
| OCD | Obsessions + compulsions | High-dose SSRI is first-line |
| Body dysmorphic disorder (BDD) | Preoccupation with imagined/slight defect in appearance | Common in dermatology/cosmetic surgery clinics; high suicide risk |
| Hoarding disorder | Persistent difficulty discarding possessions | Now a distinct diagnosis in DSM-5 |
| Trichotillomania | Recurrent hair-pulling | A "body-focused repetitive behaviour" |
| Excoriation (skin-picking) | Recurrent skin-picking | Habit reversal training helps |
| Hypochondriasis/illness anxiety | Health-related obsessions | Overlaps with OCD spectrum |
High-yield: Hoarding and excoriation disorder are new entries in the DSM-5 OC-related chapter — a frequently tested "which is new" point.
Etiology & pathophysiology
OCD is multifactorial — neurochemical, structural, genetic, and immunological factors all contribute.
1. The serotonin (5-HT) hypothesis
The dominant neurochemical theory. Evidence:
- Only serotonergic drugs (SSRIs, clomipramine) are effective; noradrenergic-selective antidepressants (e.g., desipramine) are not.
- Symptom exacerbation with the 5-HT agonist m-CPP (meta-chlorophenylpiperazine).
- Therapeutic response correlates with serotonergic potency.
High-yield: OCD responds to serotonergic antidepressants only. This selectivity is the single strongest argument for the serotonin hypothesis and a classic MCQ.
2. The cortico-striato-thalamo-cortical (CSTC) circuit
Functional imaging consistently shows hyperactivity in:
- Orbitofrontal cortex (OFC)
- Anterior cingulate cortex (ACC)
- Caudate nucleus / striatum
- Thalamus
The CSTC loop fails to "filter" intrusive thoughts. Successful treatment (drugs or CBT) normalises caudate hypermetabolism on PET — a striking demonstration that psychotherapy produces measurable brain change.
3. Dopamine & glutamate
- Dopamine dysregulation explains the tic/Tourette comorbidity and the role of antipsychotic augmentation in refractory cases.
- Glutamatergic excess underlies interest in agents like memantine, riluzole, and N-acetylcysteine as augmentation.
4. Genetics
- Strongly heritable; higher concordance in monozygotic twins.
- First-degree relatives have increased risk, especially in early-onset, tic-related OCD.
5. PANDAS / PANS — the immunological link
PANDAS = Paediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections. Abrupt-onset OCD and/or tics in a child following Group A beta-haemolytic streptococcal infection, mediated by anti-basal-ganglia antibodies (molecular mimicry, akin to Sydenham chorea).
High-yield: Sudden-onset OCD or tics in a child after a sore throat → think PANDAS. Antistreptolysin-O (ASO) titre may be raised; some respond to antibiotics/immunomodulation.
Clinical features — common symptom dimensions
OCD clusters into recognisable themes; the four classic dimensions:
| Obsession theme | Typical compulsion | Notes |
|---|---|---|
| Contamination (commonest) | Washing/cleaning | Chapped, dermatitic hands a clue |
| Pathological doubt | Checking (locks, gas, switches) | Second commonest |
| Symmetry/order | Arranging, counting, repeating | Strong tic association |
| Forbidden thoughts (aggressive, sexual, religious — scrupulosity) | Mental rituals, praying, reassurance-seeking | Often hidden due to shame |
Other features:
- Primary obsessional slowness — tasks take hours due to rituals.
- Pure obsessionals ("Pure O") — obsessions with covert mental compulsions, no overt behaviour.
- Magical thinking and need for reassurance.
High-yield: Contamination is the most common obsession and checking/washing the most common compulsions. Aggressive obsessions cause great distress but are almost never acted upon — reassure the patient.
Epidemiology
- Lifetime prevalence ~2–3%.
- Bimodal onset: early peak ~ age 10 (more in boys, tic-related) and a second around early 20s.
- Overall sex ratio roughly equal in adults; male preponderance in childhood.
- Mean onset ~20 years; onset after 50 is rare and should prompt search for organic cause.
Comorbidities
- Major depression — most common comorbidity (up to two-thirds at some point).
- Tic disorders / Tourette syndrome — strongly linked, especially early-onset male OCD.
- Other anxiety disorders, social phobia, eating disorders.
- OCPD in a minority (do not equate the two).
High-yield: A boy with early-onset OCD + motor and vocal tics → consider Tourette-related OCD; this subtype responds better to antipsychotic augmentation of the SSRI.
Diagnosis & investigation of choice
OCD is a clinical diagnosis based on DSM-5/ICD-11 criteria. There is no confirmatory lab test.
Y-BOCS — the rating scale of choice
The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) is the gold-standard instrument to quantify severity and monitor treatment response (it does not make the diagnosis).
- 10 items: 5 rate obsessions, 5 rate compulsions.
- Each item scored 0–4; total 0–40.
- Domains: time occupied, interference, distress, resistance, control.
| Y-BOCS score | Severity |
|---|---|
| 0–7 | Subclinical |
| 8–15 | Mild |
| 16–23 | Moderate |
| 24–31 | Severe |
| 32–40 | Extreme |
High-yield: Remember Y-BOCS = 10 items, max score 40, half for obsessions and half for compulsions. A ≥25–35% reduction defines treatment response in trials. CY-BOCS is the paediatric version.
Work-up to exclude mimics: thyroid function, and where late/atypical onset, neuroimaging to exclude basal ganglia lesions; ASO titre if PANDAS suspected.
Key differentials
| Condition | Distinguishing feature |
|---|---|
| OCPD | Ego-syntonic perfectionism/rigidity; no true obsessions or compulsions; not resisted |
| Generalised anxiety disorder | Worries are about real-life concerns, not senseless/ritualised |
| Schizophrenia | Thoughts are ego-syntonic/delusional, insight lost, no resistance; thought insertion is not own thought |
| Body dysmorphic disorder | Preoccupation restricted to appearance |
| Tic disorders | Tics are non-goal-directed, preceded by premonitory urge, not anxiety-driven |
| Impulse-control disorders | Acts are pleasurable/ego-syntonic (gambling), not anxiety-relieving |
| Hoarding disorder | Distress on discarding, not classical obsessions |
| Depressive ruminations | Mood-congruent, occur within a depressive episode |
High-yield: The OCD-vs-OCPD distinction is examined every year: ego-dystonic + resisted = OCD; ego-syntonic + unresisted = OCPD.
Management
A stepwise, evidence-based approach combining pharmacotherapy and psychotherapy.
Stepwise approach
First-line SSRI (high dose, adequate trial 10–12 weeks) → if partial/no response, switch to a second SSRI → trial of clomipramine → augment with low-dose atypical antipsychotic (risperidone/aripiprazole) → refer for intensive ERP → consider DBS / neurosurgery in refractory disease
1. Pharmacotherapy — drug of choice
SSRIs are first-line because of efficacy and tolerability. Key principles distinguishing OCD treatment from depression:
- Higher doses are needed than for depression (e.g., fluoxetine 60–80 mg, sertraline 200 mg, paroxetine 40–60 mg, fluvoxamine 200–300 mg, escitalopram 20 mg).
- Longer latency — judge response only after 10–12 weeks at adequate dose (vs ~4–6 weeks in depression).
- Treatment is long-term; relapse is high on discontinuation, so continue ≥1–2 years.
High-yield: OCD needs higher SSRI doses and a longer trial (10–12 weeks) than depression. This "more drug, more patience" rule is a recurrent stem.
Clomipramine — a tricyclic with potent serotonin reuptake inhibition.
- Historically the most effective single agent ("gold standard" in older texts and meta-analyses), but no longer first-line because of anticholinergic side effects, cardiotoxicity, lowered seizure threshold, and lethality in overdose.
- Useful when SSRIs fail; monitor ECG.
High-yield: Clomipramine = historically the most effective drug for OCD (highest effect size in early meta-analyses); SSRIs are first-line today due to a better safety profile. Both points are tested — read the stem carefully.
Augmentation (for refractory OCD):
- Low-dose atypical antipsychotics (risperidone, aripiprazole) — especially with comorbid tics.
- Glutamatergic agents (memantine, N-acetylcysteine) — emerging.
2. Psychotherapy — treatment of choice
Cognitive Behavioural Therapy with Exposure and Response Prevention (ERP) is the psychotherapy of choice and is as effective as medication; combination therapy is best for moderate-severe disease.
- Exposure: graded confrontation with the feared stimulus (e.g., touching a "contaminated" surface).
- Response prevention: the patient refrains from the compulsion (e.g., not washing), allowing anxiety to habituate and extinguishing the reinforcement cycle.
High-yield: ERP is the behavioural treatment of choice; the active ingredient is preventing the compulsion so anxiety habituates. CBT can normalise caudate hypermetabolism on imaging, just like drugs.
3. Refractory / severe disease
- Deep brain stimulation (DBS) of the ventral capsule/ventral striatum or subthalamic nucleus.
- Stereotactic neurosurgery — anterior cingulotomy or capsulotomy for the most severe, treatment-resistant cases.
- Transcranial magnetic stimulation (TMS) — adjunct.
Complications & prognosis
- Chronic course; waxing and waning is typical, with only a minority achieving full remission without treatment.
- Significant disability, occupational/social impairment.
- Depression and suicide risk (especially with comorbid depression or BDD).
- Dermatological damage from washing; family accommodation and marital strain.
- Prognostic markers:
- Poor prognosis: early onset, poor insight/overvalued ideas, presence of compulsions, hoarding symptoms, comorbid tics/personality disorder, longer duration before treatment.
- Better prognosis: good insight, episodic course, precipitating stressor, good premorbid function.
High-yield: Poor insight, hoarding, and comorbid tic/personality disorder predict a worse outcome.
Mnemonics & eponyms
- Obsession themes — "WORDS": Washing (contamination), Ordering/symmetry, Religious/aggressive thoughts, Doubt (checking), Slowness.
- Y-BOCS = Yale-Brown — the severity scale (max 40).
- PANDAS — strep-triggered paediatric OCD/tics (think basal ganglia antibodies, like Sydenham chorea).
- Drug rule — "High dose, long wait, serotonin only."
Recently asked / exam angle
NEET PG and INI-CET have repeatedly tested:
- Most effective historical drug for OCD → Clomipramine (and recognising that SSRIs are now first-line).
- First-line drug class → SSRIs, at high doses, for 10–12 weeks.
- Y-BOCS — what it measures (severity, not diagnosis), number of items (10), maximum score (40).
- Ego-dystonic obsessions and the OCD vs OCPD differentiation.
- Serotonin hypothesis — why noradrenergic drugs fail; m-CPP exacerbation.
- CSTC circuit / caudate hyperactivity normalising with treatment.
- PANDAS — sudden OCD/tics after streptococcal pharyngitis.
- DSM-5 reclassification — OCD removed from anxiety disorders; hoarding and excoriation as new entries.
- ERP as behavioural treatment of choice and the principle of response prevention.
- Commonest obsession (contamination) and commonest compulsion (checking/washing).
- Neurosurgery — anterior cingulotomy/capsulotomy for refractory OCD.
Rapid revision
- OCD = recurrent ego-dystonic obsessions + anxiety-relieving compulsions; symptoms are resisted and >1 hr/day.
- OCD vs OCPD: ego-dystonic & resisted (OCD) vs ego-syntonic & unresisted (OCPD).
- Commonest obsession = contamination; commonest compulsions = washing/checking.
- Only serotonergic drugs work → serotonin hypothesis; noradrenergic drugs are ineffective.
- Pathophysiology = hyperactive OFC–ACC–caudate–thalamus (CSTC) loop; caudate hypermetabolism normalises with treatment.
- First-line = high-dose SSRI, judged after 10–12 weeks; continue ≥1–2 years.
- Clomipramine = historically most effective drug; reserved due to cardiotoxicity/anticholinergic effects.
- Augment with low-dose atypical antipsychotic (esp. comorbid tics) in refractory cases.
- ERP (CBT) is the psychotherapy of choice — prevent the compulsion so anxiety habituates.
- Y-BOCS: 10 items, max 40; measures severity, not diagnosis.
- PANDAS = abrupt paediatric OCD/tics post-streptococcal infection (anti-basal-ganglia antibodies).
- Refractory disease → DBS or anterior cingulotomy/capsulotomy; poor insight & hoarding = worse prognosis.