**Core Concept**
Korsakoff psychosis is a chronic neurological disorder caused by thiamine (vitamin B1) deficiency, most commonly due to chronic alcoholism. It primarily affects the thalamus and mammillary bodies, leading to severe memory impairment and confabulation.

**Why the Correct Answer is Right**
The hallmark feature of Korsakoff psychosis is **amnesia**, particularly anterograde amnesia—difficulty forming new memories. Patients often retain old memories but cannot recall recent events. This is due to damage in the medial thalamus and mammillary bodies, which are critical for memory consolidation. While disorientation (A) and delirium (B) may occur in early stages, they are not specific to Korsakoff’s. Coarse tremor (C) is more associated with cerebellar disorders, not this condition.

**Why Each Wrong Option is Incorrect**
Option A: Disorientation is common in delirium tremens or acute alcohol withdrawal, not the defining feature of Korsakoff’s.
Option B: Delirium is seen in acute alcohol intoxication or withdrawal, not in the chronic, memory-dominant phase of Korsakoff’s.
Option C: Coarse tremor is a cerebellar sign, typically seen in cerebellar degeneration or alcohol-related cerebellar damage, not a key feature of Korsakoff’s psychosis.

**Clinical Pearl / High-Yield Fact**
Korsakoff’s syndrome is always associated with thiamine deficiency, especially in chronic alcoholics. The most reliable sign is **anterograde amnesia**, and patients often confabulate to fill memory gaps—this is a key diagnostic clue.

✓ Correct Answer: D. Amnesia