Delusional Disorder

A 52-year-old man presents to psychiatry with a 3-year history of unwavering belief that his neighbour is deliberately poisoning his food through the ventilation system. He reports checking his meals obsessively and has installed multiple air filters in his home. He denies hearing voices or seeing visions. His affect is congruent with his beliefs—anxious and guarded. Cognitive function is intact. He has no prior psychiatric history and no substance use. His wife confirms his beliefs are not shared by family members. What is the most likely diagnosis?

A 52-year-old man from Mumbai presents to the psychiatry outpatient department with a 3-year history of unwavering belief that his neighbour is deliberately poisoning his food through the water supply. He reports that he has changed his water source multiple times, installed filters, and now drinks only bottled water from sealed containers. Despite reassurance from his family and a thorough investigation by the municipal corporation that found no contamination, he remains convinced of the plot. His mood is euthymic, he denies hearing voices, and his cognitive functions are intact. He maintains his job as an accountant and lives with his wife, though the relationship is strained due to his preoccupation. Physical examination and routine blood investigations are unremarkable. What is the most likely diagnosis?

A 48-year-old woman is referred to psychiatry by her primary care physician after 18 months of persistent belief that a famous film actor is secretly in love with her and sending her coded messages through television broadcasts. She has not attempted contact with the actor and maintains her job as a librarian without difficulty. She denies hearing voices or experiencing visual hallucinations. She has no prior psychiatric history, normal cognitive screening, and denies substance use. Her sister notes that the patient's mood and behaviour are otherwise normal. What is the most appropriate next step in management?

A 52-year-old man presents to the psychiatry clinic with a 3-year history of persistent belief that his neighbour is deliberately poisoning his food through the water supply. He reports that he has changed his locks three times, installed surveillance cameras, and drinks only bottled water from sealed containers. He denies hearing voices or seeing visions. His mood is euthymic, and he maintains his job as an accountant with no decline in occupational functioning. Mental status examination reveals intact cognition, organized thought process, and no evidence of formal thought disorder. Neurological examination and routine investigations are normal. What is the most likely diagnosis?

A 48-year-old woman is referred to psychiatry by her general practitioner after presenting with a 4-month history of unwavering conviction that a famous Bollywood actor is in love with her and sending her secret messages through his film dialogues and social media posts. She has written multiple letters to the actor's production house and has attempted to contact him through various channels. She denies hearing voices or seeing visions. Her sleep is normal, appetite is preserved, and she continues to work as a schoolteacher. Cognitive examination is intact. She becomes irritable when her beliefs are questioned but otherwise maintains appropriate affect. What is the most likely diagnosis?