Subacute combined degeneration of the cord
Description
- Vitamin B12 (cobalamin) deficiency myelopathy - symmetrical demyelination of the DORSAL and LATERAL columns, beginning in the mid-thoracic cord
- "Combined" = dorsal columns (sensory ataxia) + corticospinal tracts (spasticity)
- Often with a coexisting peripheral neuropathy - which is what produces the classic mixed picture
- *The signature examination finding: extensor plantar responses with ABSENT ankle jerks*
- Also caused by nitrous oxide (recreational "nangs", or repeated anaesthetic exposure) - increasingly the commonest cause seen in young people
- Copper deficiency produces a clinically indistinguishable myelopathy - always check both
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