Figure 51-1 Zinc toxicity and copper deficiency: Excretion of copper into the gastrointestinal tract is the major pathway that regulates copper homeostasis and prevents deficiency or toxicity. Excessive zinc ingestion is a well-recognized cause of copper deficiency. The zinc-induced inhibition of copper absorption could be the result of competition for a common transporter or a consequence of induction of metallothionein in enterocytes. Metallothionein has a higher binding affinity for copper than for zinc. Copper is retained within the enterocytes and lost as the intestinal cells are sloughed off. Failure to mobilize absorbed copper from intestinal cells forms the basis of Menkes’ disease (1). In Wilson’s disease there is decreased incorporation of copper into ceruloplasmin (2a) and impaired biliary excretion of copper (2b).

(Modified from Kumar N. Myeloneuropathy due to copper deficiency. In Fifty Neurological cases from Mayo Clinic. New York, Oxford University Press, 2004. By permission of Mayo Foundation for Medical Education and Research. All rights reserved.)

As in our patient, the most common neurologic manifestation of acquired copper deficiency is that of a myelopathy presenting with a spastic gait and prominent sensory ataxia. The myelopathy of copper deficiency closely mimics the subacute combined degeneration of vitamin B₁₂ deficiency. Clinical or electrophysiologic evidence of an associated axonal peripheral neuropathy is common. Also reported in some patients is progressive, asymmetric weakness or electrodiagnostic evidence of denervation suggestive of lower motor neuron disease.^4,7 The commonest abnormality on the spine MRI scan is increased T2-signal involving the dorsal column (Fig. 51-2). Somatosensory evoked potentials provide additional evidence of impaired central conduction.

Figure 51-2 Magnetic resonance imaging scan in copper deficiency myelopathy: Sagittal (arrowhead) (A) and axial (arrow) (B) T2-weighted MRI in a patient with copper deficiency myelopathy showing increased signal involving the dorsal column in the cervical cord.

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