Case report

A 58-year-old Caucasian male presented to our multidisciplinary team clinic for evaluation of progressively worsening, episodic muscle weakness. He had 3-5 episodes per week of generalized weakness predominantly affecting facial, trunk, and limb muscles. Episodes lasted anywhere from a few hours to days and were precipitated by exposure to cold and taking rest after strenuous exercise. Electro-diagnostic studies showed normal sensory and motor conduction studies and needle electromyography showed short duration polyphasic motor unit potentials and early recruitment in proximal muscles consistent with a myopathic process. Gene testing was positive for a pathogenic variant of SCN4A [c.2111 C>T (p. Thr704Met)]. Patient was initially treated with lifestyle changes but continued to have 3 to 5 attacks every week. Acetazolamide was then added which reduced attack rate to 3 per week, lasting several hours. Eventually, he was started on dichlorphenamide 50 mg twice a day, later increased to 100mg twice a day after two weeks which resulted in complete resolution of attacks for 2 years. 

This study demonstrated successful response to dichlorphenamide in a patient with treatment refractory hyperkalemic periodic paralysis with SCN4 gene mutation with complete resolution of attacks for over 2 year time period.