Altered axonal excitability properties and nerve edema in POEMS syndrome

POEMS (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes) syndrome is a rare cause of demyelinating neuropathy with upregulation of vascular endothelial growth factor (VEGF). This study aimed to elucidate axonal excitability properties and their relation to VEGF levels and nerve edema in POEMS neuropathy.

Axonal excitability measurement and nerve ultrasound were performed in the median nerve of 33 patients with POEMS syndrome. Serum VEGF levels were measured by ELISA.

Compared with normal subjects (n=87), POEMS patients showed longer strength-duration time constant, fanning-out of threshold electrotonus curves, and greater threshold changes in a hyperpolarizing current-threshold relationship. Nerve ultrasound showed significant enlargement in POEMS patients. Serum VEGF levels and the extent of nerve edema partly correlated with nerve conduction slowing, as well as persistent sodium currents and inward rectification.

In POEMS syndrome, patterns of changes in excitability properties could suggest increased persistent sodium currents, and impaired potassium and inward rectifying channels. The findings were not consistent with depolarization due to nerve edema and compression ischemia.

In addition to demyelination, nerve edema induced by upregulated VEGF, and upregulated inflammatory cytokines could modulate profiles of POEMS neuropathy.