Erythromelalgia: A Child With V400M Mutation in the SCN9A Gene

Erythromelalgia is a rare pain syndrome caused by gain-of-function mutations of the SCN9A gene. The gene encodes Nav1.7 channels, preferentially located in the sympathetic ganglia and nociceptive sensory neurons of the dorsal root ganglia (DRG),1 that play a key role in pain modulation.2 DRG hyperexcitability leads to decreased pain threshold and increased firing frequency of pain signaling neurons.3 Clinically, this presents as recurrent, severe burning pain, redness, warmth, and often swelling of the distal extremities. Exposure to cold may provide relief but can lead to skin ulcerations.4 There is anecdotal evidence of partial relief from NSAIDS, antihistamines, and sodium channel blockers.5,6 Carbamazepine and oxcarbazepine inactivate sodium channels but have been ineffective in most patients. Only 1 family with erythromelalgia and V400M mutation in the SCN9A gene that responded to carbamazepine was reported so far.3

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