Atypical Electrophysiological Pattern in Hypokalemic Periodic Paralysis With CACNA1S Mutation: A Case Report.

Hypokalemic periodic paralysis type 1 (PPHy-1) is a rare autosomal dominant disorder caused by mutations in the CACNA1S gene, leading to recurrent muscle weakness associated with hypokalemia. We describe a 19-year-old male presenting with recurrent episodes of muscle weakness lasting from 2 to 48 hours. During an attack, clinical examination revealed tetraparesis with axial motor deficits, but no bulbar or facial involvement. Serum potassium levels were 2.5 mmol/L, and nerve conduction studies (NCS) showed asymmetrical decrement in motor amplitudes. A long exercise test (LET) post-attack revealed pattern IV, an atypical finding for PPHy-1. Whole exome sequencing confirmed a heterozygous mutation in the CACNA1S gene, establishing the diagnosis. The patient responded well to oral potassium supplementation and prophylactic acetazolamide, which reduced the frequency of attacks. This case highlights the importance of integrating clinical, electrophysiological, and genetic findings in diagnosing PPHy-1. The unusual LET pattern IV suggests variability in the expression of PPHy-1, warranting further investigation into the variability of LET patterns in this disorder.