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]