Delusional disorder — structured clinical viva

Working diagnosis. Delusional disorder, somatic subtype (infestation belief), duration years, no prominent hallucinations, relatively preserved occupational function — partial psychosis rather than multi-domain schizophrenia. Differential includes organic skin disease (rule out once), substance use, BDD/illness anxiety with poor insight, and late medical/neurocognitive disease if new cognitive signs appear.[1][2]

Why not schizophrenia. Absence of broader Criterion A (prominent voices, disorganisation, negative symptom syndrome) and relatively preserved role function outside the somatic theme favour delusional disorder over schizophrenia.[2]

Engagement. Validate distress and sleep disruption; do not collude (“yes, parasites”) and do not ridicule specimens. Negotiate shared goals: itch control, sleep, reduce harmful self-treatments, coordinated care. Frame medication as reducing mental pressure and preoccupation so she can function — not as proof the belief is false on day one.[6][4]

Liaison and harm prevention. One thorough medical/dermatology review to exclude genuine pathology, then psychiatric leadership of the care plan to prevent endless biopsies/procedures. Agree a letter framework with GP/dermatology: investigate red flags, avoid non-indicated invasive interventions.[5][4]

Pharmacotherapy. Offer SGA trial with monitoring — e.g. aripiprazole 5–10 mg daily toward 10–15 mg, or risperidone 1–2 mg titrating carefully, or olanzapine 5–10 mg if sedation/itch sleep disruption dominates, with metabolic/EPS/prolactin/ECG-risk monitoring as indicated. Historical pimozide is an exam pearl with QTc caution, not automatic modern first line. State Cochrane: sparse high-quality DD-specific RCTs.[3][5][6][4]

Success metrics. Reduced specimen-collecting, less self-excoriation/self-treatment, better sleep, fewer emergency dermatology attendances — belief may persist partially.[6][1]

Risks. Suicide if despair when belief falters; iatrogenic medical harm; antipsychotic side effects; disengagement if alliance broken.[4]