Erythromelalgia is a rare pain syndrome caused by gain of function mutation in SCN9A gene. Clinically, this presents as recurrent episodes of severe burning pain, redness, warmth, and often swelling of the distal extremities. Cooling strategies provide some relief but can lead to severe complications. Most patients with erythromelalgia respond partially to pharmacotherapy. 

We report a 10 year old girl with a c.1198G>A, p.Val400Met (V400M) mutation in SCN9A gene, characterized as ‘likely pathogenic’, who has had acute exacerbations of excruciating pain in her calves and soles with erythema since the age of 2. This mutation has only been reported in one family with erythromelalgia who responded completely to carbamazepine.

Our patient did not respond to oral gabapentin and topical combination of amitriptyline and ketamine. Carbamazepine 100 mg ER twice daily reduced exacerbation frequency. Despite titration of carbamazepine dose up to 200 mg ER three times daily, she was still experiencing severe flare-ups that prevented her from sleeping. She was admitted to hospital for ketamine infusion and was pain free for 7 days. Following a flare-up, she was readmitted to hospital and received lidocaine infusion followed by mexiletine 150 mg orally twice daily without further exacerbations.