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

## TL;DR

A patient with erythrocytosis developed peripheral neuropathy due to a functional vitamin B12 deficiency, which was treated with phlebotomy and B12 injections.

## Contribution

Highlights a rare case where erythrocytosis and functional B12 deficiency jointly cause peripheral neuropathy.

## Key findings

- Peripheral neuropathy occurred due to both erythrocytosis and functional B12 deficiency.
- Therapeutic phlebotomy and B12 injections led to mild symptom improvement.
- The case supports a joint etiology for neuropathy in erythrocytosis patients.

## Abstract

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.