Subacute combined degeneration (progressive peripheral sensory and motor loss) is a late sign of B12 deficiency, which is common in old people. On exams, a geriatric patient who lives alone and may have a “tea and toast” diet is likely to have vitamin deficiencies, particularly of folate and B12.

Subacute combined degeneration never produces exagerated reflexes. It's one of the causes of babinski + with absent ankle reflex.

SUBACUTE COMBINED DEGENERATION (B12 deficiency):

Spinocerebellar tract -- Unconcious proprioceptive sensation. 'tingling'

Lateral Corticospinal tract -- Controls ipsilateral limb fine motion. 'weakness of extensors and flexor muscles. exaggerated reflexes'

Dorsal Column -- White matter in posterior. Made of gracille and cuneatus fasciculi. Gracile is for lower body sensory and cuneate is upper body sensory. 'decreased sensation to vibration and position'

-initially i put B6 because of descriptions of peripheral neuropathy, but the decreased vibration/proprioception was the key differentiator