Demyelinating neuropathy requires differential diagnosis with vasculitic neuropathy in rheumatoid arthritis: Significance of sural nerve electrophysiology findings

Objectives

Neuropathy is considered a complication of rheumatoid arthritis (RA), whose underlying mechanisms are mainly entrapment, drug-induced and rheumatoid vasculitis (RV). At Tokyo Women's Medical University, for the purpose of diagnosing vasculitic neuropathy, we carried out nerve and muscle biopsies in nine RA patients. Unexpectedly, we found three cases of demyelinating neuropathy, together with six cases of RV. Our aim was to investigate the neurophysiological features of demyelinating neuropathy in patients with RA, compared with those of patients with RV.

Methods

We reviewed the pathological, clinical and electrophysiological findings in patients with RA who underwent nerve and muscle biopsies. We compared patient demographics and nerve conduction study findings between patients with RV and other patients.

Results

The histological findings showed necrotizing vasculitis in six of nine patients. Vasculitis was absent in the other three patients, which showed evidence of demyelination and remyelination. The absence of a sensory nerve action potential and compound motor action potential were observed more frequently in the RV cohort. Sural sparing, shown as the sural-to-median sensory nerve action potential ratio, was significantly higher in demyelinating neuropathy patients. Treatment was corticosteroid and cyclophosphamide in RV patients, and intravenous immunoglobulin was administered to three demyelinating neuropathy patients. Treatment response was satisfactory in seven of the nine patients.

Conclusion

Demyelinating neuropathy was found more often in patients with RA neuropathy than expected. Sural nerve sparing, as well as the absence of sensory nerve action potential or compound motor action potential, are useful for the differential diagnosis of demyelinating neuropathy with RV in RA patients with neuropathy.