Okay, let's tackle this question. The patient is a 30-year-old man with paranoid symptoms. He's been suspecting his wife of an affair with his boss, and a friend is involved from abroad. He also thinks people talk ill about him. Friends tried to convince him but he's not convinced. He's otherwise normal, no thought disorder or inappropriate behavior.

First, I need to recall the differential diagnoses for paranoid symptoms. The key here is that he's not showing other symptoms like hallucinations, disorganized speech, or flat affect. So, this might point towards a specific diagnosis rather than a broader psychotic disorder.

The options are likely to include schizophrenia, paranoid disorder, delusional disorder, and maybe something like a mood disorder with psychotic features. But since the question states he's otherwise normal, that rules out schizophrenia, which would have more symptoms like thought disorder, which he doesn't have.

Delusional disorder, paranoid type, fits here because it's characterized by persistent delusions without other psychotic symptoms. The delusions are often grandiose or paranoid, like being followed or conspired against. The patient here has a delusion (wife and friend involved in a conspiracy against him) but no other symptoms like hallucinations or disorganized thinking.

Why not schizophrenia? Because the duration of symptoms here is 2 months. Schizophrenia typically requires at least 6 months of symptoms with at least one month of active symptoms. Also, schizophrenia would involve more impairments in functioning and other symptoms beyond the delusions.

Other options might include brief psychotic disorder, but that's usually shorter in duration and often precipitated by stressors, and the delusions would be part of a more acute episode. The patient here has been symptomatic for 2 months, so maybe not brief.

So the correct answer is delusional disorder, paranoid type. The key points are persistent delusions without other psychotic features, and the absence of thought disorder or inappropriate behavior.

**Core Concept**
This question tests the differential diagnosis of persistent paranoid ideation without accompanying psychotic features. Delusional disorder, paranoid type, is characterized by nonbizarre delusions in the absence of other symptoms of schizophrenia, such as hallucinations or disorganized thinking.

**Why the Correct Answer is Right**
The patient exhibits persistent paranoid delusions (conspiracy beliefs about his wife and friend) that are fixed and unshakable. There is no evidence of thought disorder, hallucinations, or impaired functioning outside the delusional content. Delusional disorder requires delusions lasting ≥1 month, which aligns with the 2-month duration here. The absence of other psychotic features distinguishes it from schizophrenia.

**Why Each Wrong Option is Incorrect**
**Option A:** Schizophrenia requires at least 6 months of symptoms with ≥1 month of active symptoms (delusions, hallucinations, disorganized speech/thinking). This patient lacks other required features.
**Option B:** Brief psychotic disorder involves sudden-onset symptoms lasting ≤1 month, not 2 months.
**Option C:** Schizoaffective disorder includes mood symptoms (depression/mania) with psychotic features, which are absent here.

**Clinical Pearl**
Delusional disorder often involves nonbizarre delusions (e.g., conspiracies, infidelity) that are logically consistent but false. Key exam trap: Differentiate from schizophrenia by the absence of other psychotic symptoms

✓ Correct Answer: B. Persistent delusion disorder