Obsessive-Compulsive Disorder (OCD)

Definition

OCD is a psychiatric condition characterized by obsessions (persistent, unwanted, intrusive thoughts, images, or impulses) and compulsions (repetitive acts or rituals performed to neutralize the anxiety from obsessions). Patients recognize the irrationality of their thoughts and behaviors - this is what distinguishes obsessions from psychotic delusions. - Adams and Victor's Principles of Neurology

Epidemiology

Lifetime prevalence: 2-3% worldwide
Affects males and females equally
Onset typically in adolescence or early adulthood, though childhood onset occurs
Course is usually waxing and waning, but can show steady deterioration in psychosocial function
Comorbidities are common: depression, other anxiety disorders, eating disorders, tics, Tourette syndrome

Clinical Features

Obsessions (thoughts)

Contamination fears (most common) - fear of germs, dirt
Harm obsessions - fear of harming self or others (patients rarely act on these)
Symmetry/ordering - things must be "just right"
Religious/blasphemous thoughts
Doubting mania - every act must be ruminated on before it is carried out

Compulsions (acts/rituals)

Repeated hand washing, bathing
Checking behaviors (locks, gas jets, appliances)
Counting, ordering, arranging objects
Hair pulling (trichotillomania)
Hoarding

DSM criterion: Obsessive-compulsive activities take up >1 hour per day and impair functioning. Patients often conceal symptoms due to embarrassment.

Physical clues

Chafed, reddened hands (from washing)
Patchy hair loss (from repetitive pulling)

Pathophysiology

The neural circuit implicated in OCD involves:

Orbital frontal cortex
Caudate nucleus (involved in habit and skill learning)
Globus pallidus

Successful treatments that reduce OCD symptoms also decrease metabolic activity in the caudate nucleus. A genetic contribution is supported by twin studies. OCD aggregates with Tourette syndrome in families, and both are more common in males and first-born children. A 2025 genome-wide meta-analysis (PMID: 40360802) identified 30 genomic loci associated with OCD, advancing our understanding of its genetic basis.

Treatment

First-Line Pharmacotherapy

Drug	Dose Range	Notes
Fluoxetine	5-60 mg/d	FDA approved for adults and children
Fluvoxamine	25-300 mg/d	FDA approved for adults and children
Sertraline	50-150 mg/d	FDA approved for adults and children
Paroxetine	40-60 mg/d	Adults only
Clomipramine	25-250 mg/d	TCA; approved but poorly tolerated (anticholinergic, sedative side effects); efficacy is unrelated to its antidepressant activity

Only 50-60% of patients show adequate improvement with pharmacotherapy alone. - Harrison's 22E

Augmentation for Treatment-Resistant OCD

Buspirone (serotonergic agent)
Antipsychotics (neuroleptic augmentation)
Benzodiazepines
High-dose theta burst repetitive TMS (rTMS)
Closed-loop deep brain stimulation (DBS) for severe, refractory cases

A 2025 network meta-analysis (PMID: 39477076) found brain stimulation modalities (including TMS and DBS) have meaningful efficacy for OCD.

Psychotherapy (First-Line, often preferred)

Cognitive Behavioral Therapy (CBT) with Exposure and Response Prevention (ERP) is as effective as medication, particularly for patients with time-consuming compulsions
Techniques include:
- Gradual increase in exposure to feared stimuli
- Maintaining a diary to identify stressors
- Homework substituting new behaviors for compulsions

When a therapeutic response is achieved, long-duration maintenance therapy is usually indicated given OCD's chronic course.

Key Differentiators

Feature	OCD	Psychosis
Insight	Preserved (ego-dystonic)	Absent (ego-syntonic)
Nature of thoughts	Unwanted, distressing	Believed to be real
Response to treatment	SSRIs + CBT	Antipsychotics

Sources: Harrison's Principles of Internal Medicine 22E; Adams and Victor's Principles of Neurology 12E; Kaplan and Sadock's Synopsis of Psychiatry

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