Delusional Disorder

Delusional disorder is one or more delusions lasting at least one month, without prominent hallucinations or disorganisation, and with relatively preserved function outside the delusional domain.

• Prevalence 0.2%, mean onset around 40 years; women slightly more often.
• Subtypes: persecutory, jealous, erotomanic, grandiose, somatic, mixed.
• Associated: social isolation, immigration, sensory impairment (deafness), family history.
• Risk of violence in jealous and erotomanic types; marked reluctance to seek treatment.

• Fixed, systematised, nonbizarre delusions (being followed, partner infidelity, infestation, illness).
• Mood congruent but mood episodes brief; behaviour normal apart from delusion; litigious or stalking behaviour.
• Lack of insight, referrals via family, police or dermatology (delusional infestation).

• DSM-5 criteria, with exclusion of schizophrenia, mood disorder with psychotic features, OCD, body dysmorphic disorder, dementia, substance induced and medical conditions.
• Investigations: toxicology, TSH, B12, folate, glucose, HIV, syphilis, MRI brain (stroke, tumours), EEG, medication review (dopaminergic drugs, steroids).
• Risk assessment for violence, suicide, and impact on others.
• Collateral history.

• Build a therapeutic alliance, avoid confronting the delusion, engage with associated distress.
• Antipsychotics: risperidone 1 to 4 mg daily, olanzapine 5 to 15 mg, aripiprazole, amisulpride 200 to 400 mg; pimozide 2 to 8 mg for monosymptomatic hypochondriacal (somatic) type with ECG; response in about 50%.
• CBT adapted for delusions; treat comorbid depression with SSRI.
• Compulsory admission only for significant risk; consider long acting injectables in nonadherence.
• Treat sensory deficits and isolation; regular long term follow up.