Subacute combined degeneration affects which neural tracts?

• A. Dorsal columns and lateral corticospinal tracts.
• B. Corticospinal and spinothalamic tracts.
• C. Cerebellar peduncles.
• D. Basal ganglia.

Answer: (A)

Subacute combined degeneration arises from vitamin B12 deficiency causing demyelination in the spinal cord, most notably affecting two major pathways: the dorsal columns, which carry fine touch, vibration, and proprioception, and the lateral corticospinal tracts, which control voluntary movement. Damage to these tracts produces the characteristic mix of sensory loss (especially vibration and proprioception) with motor weakness from corticospinal tract involvement, leading to sensory ataxia and spastic paresis. The other structures listed aren’t the classic sites for this pattern: cerebellar peduncles would disturb coordination from cerebellar pathways, the basal ganglia relate to movement disorders rather than the combined sensory-motor pattern seen here, and the spinothalamic tracts would mainly affect pain and temperature sensation, not the proprioceptive and motor deficits that define this condition.