A 30 year old man since 2 months suspects that his wife is having an affair with his boss. He thinks his friend is also involved from abroad and is providing technology suppo. He thinks people talk ill about him. His friends tried to convince him but he is not convinced at all. Otherwise he is normal, he doesn't have any thought disorder or any other inappropriate behavior. The most likely diagnosis is:

B i.e. Persistent delusional disorderIn delusion disorder, patient presents with circumscribed systematized usually single non bizarre (i.e. involving real life situation) delusional system with relative sparing of surrounding personality and behaviour (in other areas) for atleast 1 month. There is absence of prominent hallucinations, disorganized speech and behaviour. However, in schizophrenia there are multiple (may be bizzare) delusions, hallucinations, with deterioration in over all personality & behaviour.Patients suffering from delusional disorder do not regard themselves as mentally ill and actively oppose psychiatric referral. Because they may experience little impairment, they generally remain outside hospital settings, appearing reclusive, eccentric, or odd, rather than ill.The patient in question is only having persistent delusion of infidelity about his wife. Otherwise he doesn't have any thought disorder, or any inappropriate behavior. Symptoms have been present for 2 months (i.e. > 1 month) so the diagnosis is persistent delusional disorder.Personality disorder always appear in childhood or adolescence and continues into adulthood.