MYASTHENIA & RELATED DISORDERS: P.35 Improvement of strength and muscle MRI with dichlorphenamide in hypokalemic periodic paralysis myopathy: A case report

Abstract

Hypokalemic periodic paralysis (hypoPP) is an autosomal dominant channelopathy characterized by episodes of muscle paralysis followed by progressive proximal weakness later in the course of the disease. Dichlorphenamide (DCP) is approved by the FDA for hypokalemic periodic paralysis based on its ability to prevent acute weakness episodes. Its effect on chronic weakness or muscle MRI findings has not been studied. The patient is a 74-year-old man with hypoPP with a c.1583 G>A pathogenic mutation in the CACNA1S gene who presented with progressive proximal lower extremity weakness and muscle atrophy. He had episodes of weakness as a teenager and was diagnosed in his early 20s after an episode of severe weakness. He has been taking potassium supplementation for many years. He had been treated with acetazolamide without improvement. For about 15 years prior to presentation to our neuromuscular clinic, he developed progressive lower extremity weakness, without noting episodes of paralysis. Acetazolamide was discontinued, and DCP was initiated. Prior to the initiation of DCP, muscle MRI of the lower extremities revealed muscle atrophy with fatty replacement, and intramuscular edema. MRI of the lower extremities after the initiation of DCP revealed improvement in the edema. The patient reported improvement in gait and posture and no progression of weakness. Sit to stand time improved from 2.7 seconds to 2.2 seconds. This case supports a role for DCP in the treatment of progressive weakness associated with hypoPP and suggests a role for DCP beyond the prevention of paralytic episodes.