(Kiosk 3) Severe Peripheral Neuropathy After Excessive Zinc Consumption for COVID-19 Prophylaxis Leading to Copper Deficiency: A Case Report

Case Diagnosis: Neuropathy

Case Description or Program Description: 73-year-old male with a history of metastatic squamous cell carcinoma of the left base of tongue treated with radiation and chemotherapy was referred to our services for 7-8 months of worsening neuropathy in Jan 2022. On presentation the patient had primarily diminished sensation which had ascended to his xiphoid process from his bilateral lower extremities, and distal upper extremities. Additionally, patient noted proprioceptive loss over bilateral great toes causing imbalance.

Setting: Outpatient cancer pain and rehabilitation clinic.

Assessment/Results: Following the patient's workup, copper levels were found to be extremely low at 8 mcg/dL (normal: 85-180 mcg/dL). It was then discovered that the patient was taking excessive amounts of zinc containing supplements with the thought that it would help protect from COVID-19 infection. His zinc level was found to be elevated at 129 mcg/dL (normal: 80-120 mcg/dL).

Discussion (relevance): This patient was experiencing progressive ascending numbness and severe burning from his distal extremities to his xiphoid process. Ingesting large quantities of zinc may inhibit the absorption of metals into the body through the increased production of metallothionien, which binds to copper with higher affinity than zinc. Copper is then lost via the shedding of enterocytes. As copper is required for many cellular processes in the body, such a deficiency may result in disruption of normal homeostatic molecular cycles, e.g. the methylation cycle – a proposed mechanism of how copper deficiency may mimic subacute combined degeneration myelopathy. Additionally, copper deficiency can lead to axonal degradation and epineural inflammation as evidenced by biopsy thereby possibly resulting in sensory predominant neuropathy.

Conclusions: In the setting of the COVID-19 era, it is increasingly important to thoroughly gather supplement history from patients for possible toxic levels of consumption of zinc or other metals, especially as this patient’s presentation was presumed chemotherapy-induced. This case exemplifies the broad differential for ascending neuropathy as copper deficiency may mimic this pathology.