Clinical, physiological and pathological characterisation of the sensory predominant peripheral neuropathy in copper deficiency.

INTRODUCTION: Myelopathy is considered the most common neurological complication of copper deficiency. Concurrent peripheral neuropathy has been recognised in association with copper deficiency but has not been well characterised. OBJECTIVES: To characterise the clinical, physiological and pathological features of copper-deficient peripheral neuropathy. METHODS: Patients with simultaneous copper deficiency (<0.78 µg/mL) and peripheral neuropathy seen at the Mayo Clinic from 1985 to 2005 were identified. RESULTS: 34 patients were identified (median age 55 years, range 36-78) including 24 women and 10 men. Myelopathy was found in 21 patients. Median serum copper level was 0.11 µg/mL (range 0-0.58). The most frequent clinical and electrophysiological pattern of neuropathy was a sensory predominant length-dependent peripheral neuropathy (71%). Somatosensory evoked potentials demonstrated central slowing supporting myelopathy (96%). Quantitative sensory testing demonstrated both small and large fibre involvement (100%). Autonomic reflex screens (77%) and thermoregulatory sweat test (67%) confirmed sudomotor dysfunction. 14 cutaneous nerve biopsies revealed loss of myelinated nerve fibres (86%), increased regenerative clusters (50%), increased rates of axonal degeneration (91%) and increased numbers of empty nerve strands (73%). 71% of biopsies demonstrated epineurial perivascular inflammation. CONCLUSIONS: An axonal, length-dependent sensory predominant peripheral neuropathy causing sensory ataxia is characteristic of copper deficiency usually co-occurring with myelopathy. Neurophysiological testing confirms involvement of large, greater than small fibres. The pathological findings suggest axonal degeneration and repair. Inflammatory infiltrates are common but are small and of doubtful pathological significance.