Zinc-Induced Copper Deficiency Myeloneuropathy Masquerading as Paraneoplastic Syndrome: A Case Report.

Copper deficiency is a rare but reversible cause of myeloneuropathy, often overlooked in patients presenting with progressive neurological deficits. Excessive zinc intake, particularly from denture adhesives, can lead to copper depletion through competitive inhibition of intestinal absorption. We present the case of a 63-year-old female with a history of chronic obstructive pulmonary disease (COPD), Stage IIIA triple-negative breast cancer (TNBC) (status post mastectomy with adjuvant therapy), peripheral neuropathy, and a prior cecal adenoma who was admitted for hematochezia and progressive generalized weakness over several weeks. Imaging revealed a suspicious 1.4 cm pulmonary nodule in the left lower lobe and a 2.6 cm x 1.8 cm x 1.5 cm destructive lytic lesion in the left parietal bone. Given her worsening lower extremity weakness, concern for a paraneoplastic syndrome prompted a lumbar puncture and paraneoplastic antibody panel, both of which were negative. The patient underwent a five-day course of intravenous immunoglobulin (IVIG) without improvement. Further metabolic workup revealed profound copper deficiency of 417 µg/L (reference range: 810-1,990 µg/L). Upon further questioning, the patient reported chronic use of zinc-containing denture adhesive. She was initiated on copper supplementation with significant neurological improvement over several months, transitioning from being wheelchair bound to ambulating with a walker. Pathology from resection of the skull lesion revealed a World Health Organization (WHO) grade 1 meningioma, while the lung lesion was treated with CyberKnife, confirming Stage IA squamous cell carcinoma. This case highlights the importance of considering nutritional deficiencies in patients with symptoms of progressive myeloneuropathy, such as gait disturbances, sensory ataxia, or spasticity, particularly in those with risk factors such as chronic denture adhesive use. Clinicians should maintain a high index of suspicion for copper deficiency in cases mimicking paraneoplastic syndromes.