Peripheral Neuropathy Secondary to a Functional Vitamin B12 Deficiency in the Setting of Erythrocytosis.

Peripheral neuropathy can be a rare symptom of erythrocytosis through an ischemia-related mechanism. Vitamin B12 deficiency is another cause of peripheral neuropathy through the impaired maintenance of peripheral myelin sheaths. Patients with myeloproliferative disorders causing erythrocytosis can present clinically with functional, symptomatic vitamin B12 deficiencies despite normal serum levels. We present a case of peripheral neuropathy occurring secondary to both erythrocytosis and a functional B12 deficiency. The patient's pattern of peripheral neuropathy could not be explained by erythrocytosis alone, supporting a joint etiology involving a functional B12 deficiency. The patient was treated with therapeutic phlebotomy and vitamin B12 injections to address both underlying causes of his symptoms. He was discharged to follow up with an outpatient hematologist and reported mild symptom improvement at the two-week and one-month follow-up appointments.