Obsessive-compulsive disorder

Definition. Obsessions are recurrent, intrusive, unwanted thoughts, images or urges causing marked anxiety and recognised as one's own. Compulsions are repetitive behaviours or mental acts performed to reduce that anxiety, according to rigid rules. They are time-consuming (more than one hour a day) or cause marked distress or impairment. DSM-5 moved OCD out of the anxiety disorders into "Obsessive-Compulsive and Related Disorders", alongside body dysmorphic disorder, hoarding disorder, trichotillomania and excoriation disorder.

Epidemiology in old age. Prevalence is around 1% in older adults, and most cases are long-standing, with onset in adolescence or early adulthood, persisting into old age. Common themes are contamination and washing, checking, symmetry, and religious or somatic obsessions; in late life, hoarding disorder is disproportionately common and overlaps with severe self-neglect (Diogenes syndrome).

The critical rule — new-onset OCD in old age is organic until proved otherwise. True de novo OCD after 60 is rare. Investigate for frontal lobe and basal ganglia pathology — stroke (especially caudate and basal ganglia), frontotemporal dementia, Parkinson's disease, Huntington's disease, tumour and head injury — and for drug effects, notably dopamine agonists causing punding and impulse-control behaviours.

Differential diagnosis. Obsessive-compulsive personality disorder — ego-syntonic traits without true obsessions or compulsions, and one of the commonest personality disorders in old age. Also: depression with ruminations (mood-congruent and not resisted), generalised anxiety (worries concern real-life problems), dementia with repetitive or stereotyped behaviour, psychosis with delusions (no insight, not resisted), and hoarding disorder.

Assessment. Direct enquiry, since patients rarely volunteer symptoms because of shame; informant history; rate severity with the Yale-Brown Obsessive Compulsive Scale (Y-BOCS); screen for depression, present in up to two-thirds, and for suicidality; assess functional and carer impact. Neuroimaging and cognitive testing where onset is late or the presentation atypical.

Management. CBT with exposure and response prevention (ERP) is first-line and effective in older adults. Drugs — SSRIs are first-line, but note that OCD requires higher doses and longer trials (10–12 weeks) than depression does; clomipramine is effective but its anticholinergic, orthostatic and cardiac effects make it a poor choice in the elderly. For resistant cases, augmentation with a low-dose atypical antipsychotic (risperidone, aripiprazole). Avoid benzodiazepines — ineffective for OCD and harmful in old age.

Neuromodulation for OCD (2023–2025). Transcranial magnetic stimulation is approved for treating OCD as well as for antidepressant-resistant depression, and deep TMS using the H7 coil, targeting the medial prefrontal and anterior cingulate cortex, now carries the strongest evidence for treatment-refractory OCD. Because TMS carries lower risk than high-dose antidepressants in older adults, it is an increasingly attractive option — but it must be used judiciously in those at risk of seizures, such as after stroke or traumatic brain injury. Deep brain stimulation remains reserved for the most severe refractory cases.