**Question:** All except in Brown-Séquard syndrome -

A. Spinal cord injury
B. Multiple sclerosis
C. Amyotrophic lateral sclerosis (ALS)
D. Parkinson's disease

**Core Concept:** Brown-Séquard syndrome is a neurological condition characterized by spinal cord injury. It results from unilateral sectioning of the spinal cord, leading to sensory loss on the affected side and motor deficits on the opposite side.

**Why the Correct Answer is Right:**

Correct answer D (Parkinson's disease) is not related to Brown-Sequard syndrome because Parkinson's disease is a neurodegenerative disorder characterized by motor symptoms, such as tremors, rigidity, bradykinesia, and postural instability. It does not involve spinal cord injury or sensory loss.

Correct answer C (Amyotrophic lateral sclerosis, or ALS) is incorrect because ALS is a neurodegenerative disorder affecting motor neurons, leading to muscle weakness and atrophy, but not sensory loss or motor deficits on the opposite side. ALS and Brown-Séquard syndrome have different clinical presentations and pathophysiology.

Correct answer A (Spinal cord injury) is partially correct but lacks specificity. Brown-Séquard syndrome is a specific manifestation of spinal cord injury, characterized by sensory loss on the affected side and motor deficits on the opposite side.

**Why Each Wrong Option is Incorrect:**

Option B (Multiple sclerosis) is incorrect because multiple sclerosis is an autoimmune disorder affecting the central nervous system, leading to demyelination and axonal damage. It does not result in Brown-Séquard syndrome's sensory loss and motor deficits.

**Clinical Pearl / High-Yield Fact:**

Brown-Séquard syndrome is a useful clinical clue to differentiate it from other neurological conditions. When a patient presents with sensory loss and motor deficits on different sides, it helps narrow down the differential diagnosis, guiding further investigations and treatment strategies. In this case, it differentiates Brown-Séquard syndrome from other conditions like multiple sclerosis and ALS, which have distinct clinical presentations and pathophysiology.