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Zinc-Induced Copper Deficiency Myelopathy — SCE Neurology MCQ

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HardPeripheral Neuropathy & NeuromuscularZinc-Induced Copper Deficiency MyelopathySCE Neurology

A 60-year-old man presents with progressive gait difficulty and bilateral leg stiffness over 18 months. MRI spine shows extensive dorsal thoracic cord T2 hyperintensity. He has no history of radiation exposure, surgery, or MS. Serum copper is low, serum zinc is elevated. He has been taking zinc supplements for 2 years for supposed immune benefits. What is the mechanism of his myelopathy?

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Correct answer: A — Zinc-induced copper deficiency causing myelopathy — excess zinc blocks intestinal copper absorption via competitive metallothionein binding

Explanation lettering: B = shown as A · C = shown as B · E = shown as C · A = shown as E

Excess zinc supplementation induces copper deficiency by upregulating metallothionein in enterocytes. Metallothionein has a higher affinity for copper than zinc, trapping dietary copper in enterocytes and preventing its absorption. This leads to copper deficiency, which causes a myelopathy resembling subacute combined degeneration (dorsal column and corticospinal tract involvement) and a haematological picture of sideroblastic anaemia and neutropenia. Treatment involves stopping zinc and oral or IV copper replacement. A: Zinc is not directly neurotoxic at these levels. C/D: Zinc does not cause B12 or folate deficiency. E: Zinc does not cause iron overload.

Reference: Kumar et al. Copper Deficiency Review; ABN Myelopathy Guidelines