OCD and Related Disorders

Genetic / neurodevelopmental (non-modifiable)

• Family history: A first-degree relative with OCD is the single strongest predictor; risk is highest when the proband had childhood-onset disease. Twin data support the substantial heritability already noted for this disorder.
• Tic disorders and Tourette syndrome: Tic-related OCD is a recognized DSM-5-TR specifier — earlier onset, male predominance, symmetry/"just-right" and sensory phenomena rather than contamination fear. Shares CSTC circuit pathology with tics.
• Sex and age of onset: Males present earlier (often prepubertal, more tic-related); females predominate slightly in adult-onset disease.
• Peripartum period: Pregnancy and the postpartum are established windows for new onset or exacerbation, classically with intrusive harm obsessions about the infant.

Immune / infectious

• PANDAS/PANS: Abrupt, dramatic onset of obsessions, compulsions, tics, and emotional lability in a prepubertal child following group A streptococcal infection; proposed mechanism is molecular mimicry with anti-basal ganglia antibodies. Document the strep exposure — untreated pharyngitis is the modifiable element.
• Sydenham chorea: Rheumatic fever's neurologic manifestation carries a high rate of obsessive-compulsive symptoms, reinforcing the basal ganglia model.

Environmental / modifiable

• Childhood maltreatment and stressful life events: Trauma and acute stressors precipitate or worsen symptoms in vulnerable individuals; they do not by themselves cause OCD.
• Substances and drugs: Stimulants (amphetamine, cocaine) and dopaminergic agents can provoke stereotyped, compulsive behavior; DSM-5-TR requires excluding substance-induced obsessive-compulsive and related disorder before diagnosing OCD.
• Reinforcement learning: Each compulsion terminates anxiety, negatively reinforcing the ritual — the behavioral rationale for why exposure and response prevention, not reassurance, is the corrective intervention.

• Orbitofrontal cortex (OFC) hyperactivity: The OFC shows increased activation and is responsible for error detection and behavioral inhibition; hyperactivity leads to persistent perception of threat and the need to perform corrective behaviors (compulsions)

• Anterior cingulate cortex (ACC) dysfunction: Involved in conflict monitoring and emotional regulation; abnormal activation contributes to anxiety and the sense that "something is not right"

• Striatal abnormalities: The caudate nucleus and putamen show altered activity; disrupted communication between cortex and striatum impairs the ability to suppress unwanted thoughts and behaviors

• Cortico-striato-thalamo-cortical (CSTC) circuit dysfunction: Hyperactivity in this circuit creates a feedback loop where intrusive thoughts trigger anxiety, which drives compulsions; compulsions temporarily reduce anxiety, reinforcing the cycle

• Serotonin (5-HT) dysregulation: Reduced serotonergic neurotransmission in the CSTC circuit is implicated; explains selective serotonin reuptake inhibitor (SSRI) efficacy

• Glutamate dysregulation: Emerging evidence suggests excessive glutamatergic signaling, particularly in N-methyl-D-aspartate (NMDA) receptor systems, contributing to OCD pathophysiology

• Genetic and environmental factors: Strong genetic component (heritability ~40-50%); environmental triggers include childhood trauma, infections (PANDAS—Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections), and stressful life events

Classic OCD Presentations

• Contamination obsessions with washing/cleaning compulsions: Patient fears contamination from germs, chemicals, or bodily fluids; performs excessive hand-washing, showering, or cleaning rituals that can cause dermatitis; often accompanied by checking behaviors

• Harm obsessions with checking/reassurance-seeking compulsions: Intrusive thoughts about harming self or others (e.g., "Did I hit someone with my car?"); drives repeated checking, returning to verify, or seeking reassurance; crucial distinction: patient does NOT want to harm others (ego-dystonic)

• Symmetry/ordering obsessions with arranging compulsions: Need for things to be "just right," symmetrical, or in perfect order; arranging, counting, or organizing behaviors that consume hours daily

• Intrusive sexual or religious thoughts: Obsessions about taboo sexual content, pedophilia, or blasphemy; compulsions may include mental rituals, prayer, or reassurance-seeking; causes profound shame and is commonly underreported

• Scrupulosity (religious obsessions): Excessive concern about sin, blasphemy, or moral imperfection; compulsions include excessive prayer, confession, or reassurance from clergy

Important Clinical Features

• Ego-dystonic nature: Patients recognize obsessions as irrational and unwanted (unlike psychotic delusions); this insight distinguishes OCD from psychotic disorders

• Time-consuming: Obsessions and compulsions consume at least 1 hour per day (per DSM-5) and often much longer; significantly impairs functioning

• Anxiety and distress: Obsessions trigger marked anxiety or disgust; compulsions provide temporary relief but anxiety rapidly returns

• Mental compulsions: Not all compulsions are observable behaviors; mental compulsions (counting, praying, mentally reviewing, reassurance-seeking conversations) are equally disabling

• Avoidance behaviors: Patients may avoid triggers (contaminated objects, highways, situations), leading to progressive restriction of activities

Diagnostic Criteria (DSM-5)

• Obsessions: Recurrent and persistent thoughts, urges, or images that are intrusive, unwanted, and cause marked anxiety or distress; patient attempts to suppress or ignore them

• Compulsions: Repetitive behaviors (hand-washing, checking, arranging) or mental acts (counting, praying, reviewing) performed to reduce anxiety from obsessions or prevent feared consequences; must be time-consuming or cause significant distress

• Time criterion: Obsessions and/or compulsions consume ≥1 hour per day on average (may fluctuate)

• Functional impairment: Significant distress or interference with occupational, social, academic, or personal functioning

• Not attributable to substances or medical conditions: Rule out hyperthyroidism, neurological conditions, amphetamine use

Diagnostic Tests and Approach

• Clinical interview focused on content and function: Ask directly about obsessions and compulsions; assess time spent, distress level, and functional impact; use the Y-BOCS (Yale-Brown Obsessive-Compulsive Scale) to quantify severity (scores 0-40; mild <8, moderate 8-15, severe 16-23, very severe ≥24)

• Differential diagnosis consideration:
• Distinguish from generalized anxiety disorder (GAD has worry, not obsessions; no compulsions)
• Distinguish from major depressive disorder (OCD has ego-dystonic obsessions; rumination in depression is ego-syntonic)
• Distinguish from psychotic disorders (OCD has insight; psychosis does not)
• Distinguish from body dysmorphic disorder (BDD focuses on perceived body defect; OCD is broader)

• Screen for comorbidities: Depression (affects 50-60% of OCD patients), anxiety disorders, substance use; assess suicide risk, as OCD with depression carries increased risk

• Laboratory/imaging: No specific lab tests diagnose OCD; neuroimaging shows the circuit abnormalities described above but is not used clinically for diagnosis

First-Line Pharmacotherapy

• SSRIs are gold standard: Higher doses needed than for depression; typical effective doses are fluoxetine 40-80 mg/day, sertraline 50-200 mg/day, paroxetine 40-60 mg/day, citalopram 20-40 mg/day; allow 8-12 weeks at therapeutic dose before assessing response (longer than for depression)

• Clomipramine (tricyclic antidepressant): Alternative first-line agent; particularly effective for OCD; typical dose 100-250 mg/day; anticholinergic side effects limit use but equal efficacy to SSRIs

First-Line Psychotherapy

• Cognitive-Behavioral Therapy (CBT) with Exposure and Response Prevention (ERP): Gold standard psychological treatment; patient is exposed to anxiety-triggering stimuli (contaminated object, thought of harming) and resists performing compulsions to allow anxiety to naturally habituate; requires 12-20 sessions typically; efficacy rivals medication alone and combines well with pharmacotherapy

Combined Treatment

• SSRIs + ERP superior to either alone; recommended approach for moderate-to-severe OCD

Second-Line and Augmentation Strategies

• Augmentation of SSRIs: Add antipsychotics (risperidone, aripiprazole, quetiapine) when partial response to SSRI; particularly effective for OCD with poor insight

• Switch to alternative SSRI if inadequate response after 8-12 weeks

• Clomipramine trial if SSRIs ineffective

• Psychological augmentation: Acceptance and Commitment Therapy (ACT) or metacognitive therapy for comorbid depression or treatment-resistant cases

Resistant OCD (10-15% of cases)

• Augmentation with antipsychotics (risperidone 1-6 mg/day most evidence)
• N-acetylcysteine (NAC): Emerging evidence; glutamate modulator; 2-3 g/day
• **Deep brain stim

Complications of the disorder

• Suicide — emergency: Suicidal ideation and attempts are elevated in OCD, driven largely by comorbid major depression, severe symptom burden, and shame over taboo obsessions. Screen at every visit; body dysmorphic disorder carries a particularly high suicide risk.
• Irritant hand dermatitis and secondary skin infection: Repetitive washing strips the epidermal barrier; look for fissured, lichenified hands with cellulitis as the signal complication.
• Nutritional and fluid compromise: Contamination fears about food or restricted bathroom access lead to weight loss and dehydration, especially in severe pediatric cases.
• Occupational and academic collapse: Hours consumed by rituals, plus progressive avoidance, produce disability out of proportion to the patient's insight.
• Related-disorder complications: Trichotillomania with trichophagia can produce a trichobezoar, and gastric outlet obstruction or a tail extending into the small bowel (Rapunzel syndrome) is a surgical emergency. Excoriation disorder causes ulceration and cellulitis. Hoarding disorder creates fire load, fall risk, and unsanitary living conditions — a public-safety issue often requiring adult protective services.

Complications of treatment

• Serotonin syndrome — emergency: Highest risk when clomipramine is combined with an SSRI, or when fluvoxamine (a CYP1A2 inhibitor) raises clomipramine levels. Triad of autonomic instability, altered mental status, and neuromuscular hyperactivity with clonus and hyperreflexia, lower extremities greater than upper.
• Clomipramine toxicity: Dose-dependent lowering of the seizure threshold (risk rises at the top of the therapeutic range), anticholinergic burden, orthostasis, and QRS widening in overdose — treat cardiotoxicity with sodium bicarbonate.
• SSRI class effects: FDA boxed warning for suicidality in patients under 25 — monitor closely after initiation and dose increases; citalopram carries an FDA dose limit for QT prolongation (lower ceiling in older adults and hepatic impairment); SIADH-mediated hyponatremia in the elderly; abrupt paroxetine withdrawal produces a flu-like discontinuation syndrome.
• Antipsychotic augmentation: Metabolic syndrome, akathisia (may be misread as worsening agitation), and tardive dyskinesia with prolonged use.
• ERP: Transient anxiety surge during exposures drives dropout; this is expected habituation physiology, not treatment failure.

• Ego-dystonic vs ego-syntonic is the whole question: OCD obsessions are unwanted and distressing; the perfectionism, rigidity, and preoccupation with rules in obsessive-compulsive personality disorder feel correct to the patient and involve no true compulsions. OCPD is the most common distractor in a Step 2 CK stem.
• Higher dose, longer trial: SSRIs for OCD require doses above the antidepressant range and a full 8–12 weeks at target before declaring failure — the classic wrong answer is switching agents at 4 weeks.
• Clomipramine is the only TCA with a specific OCD indication and is the most serotonergic TCA. It is not first-line only because of anticholinergic, seizure, and cardiac conduction risk — not because it is less effective.
• CBT with ERP is the single best next step for mild disease, and combined ERP plus SSRI is the answer for moderate-to-severe illness per the APA practice guideline. Reassurance-giving by the physician is countertherapeutic — it functions as a compulsion.
• Benzodiazepines do not treat OCD: They blunt anxiety without addressing the obsession-compulsion loop and undermine exposure-based habituation. Never the correct maintenance answer.
• The association examiners love is tics: A boy with symmetry/"just-right" obsessions plus motor and vocal tics has tic-related OCD; antipsychotic augmentation has the best evidence in this subgroup.
• Abrupt onset in a prepubertal child after sore throat = PANDAS; check for recent group A streptococcal infection (throat culture, antistreptolysin O titer).
• Poor insight is a DSM-5-TR specifier, not psychosis: A patient fully convinced their fear is realistic still has OCD, not schizophrenia — the content is a single circumscribed fear, without hallucinations or thought disorder.
• Related disorders diverge in treatment: Trichotillomania and excoriation disorder respond best to habit reversal training; hoarding disorder responds poorly to standard OCD pharmacotherapy and needs tailored CBT; body dysmorphic disorder worsens after cosmetic procedures — refer for SSRI and CBT instead.