**Question:** A patient with previous spells of diplopia, ataxia, dysphagia, and dizziness becomes acutely comatose. The most likely cause is

A. Encephalitis
B. Subarachnoid haemorrhage
C. Acute cerebellar ataxia
D. Subarachnoid haemorrhage

**Correct Answer:** D. Subarachnoid haemorrhage

**Core Concept:**
Subarachnoid haemorrhage (SAH) is a type of stroke caused by bleeding within the subarachnoid space, which is the space surrounding the brain. SAH can lead to neurological symptoms and signs, including the mentioned symptoms: diplopia (double vision), ataxia (incoordination), dysphagia (difficulty swallowing), and dizziness. Acute coma is a severe neurological deficit and indicates a worsening of the patient's condition.

**Why the Correct Answer is Right:**
In this case, the patient presents with a history of neurological symptoms and signs, followed by acute coma. Given the clinical picture, the most likely cause is subarachnoid haemorrhage (SAH), which can lead to these symptoms and signs due to bleeding within the subarachnoid space causing damage to the brain.

**Why Each Wrong Option is Incorrect:**
A. Encephalitis (infectious inflammation of the brain) can present with similar symptoms but typically does not lead to coma unless severe and uncontrolled.
B. Subarachnoid haemorrhage (SAH) is the correct answer, but the other options are incorrect for the following reasons:
C. Acute cerebellar ataxia is a type of cerebellar dysfunction, which can present with ataxia but typically does not cause coma unless severe.
D. Subdural haemorrhage (SDH) involves bleeding between the dura mater (covering of the brain) and the pia mater (innermost layer of the brain coverings), whereas SAH occurs within the subarachnoid space.

**Clinical Pearls:**
1. SAH is a life-threatening condition that requires urgent evaluation and intervention. Its early recognition is crucial for timely management and improved patient outcomes.
2. Neurological deterioration, particularly to coma, warrants a high index of suspicion for SAH, as the patient's condition can rapidly deteriorate, necessitating prompt neuroimaging and neurosurgical intervention if necessary.
3. While SAH can result from various causes, including aneurysmal rupture, arteriovenous malformation rupture, or trauma, the key clinical features in this scenario are the neurological deficits and coma.