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

TL;DR

A 19-year-old man with a CACNA1S gene mutation showed atypical electrophysiological patterns in hypokalemic periodic paralysis, emphasizing the need for combined clinical and genetic assessments.

Contribution

The case presents an atypical long exercise test pattern (pattern IV) in PPHy-1, suggesting variability in the disorder's electrophysiological expression.

Findings

The patient exhibited tetraparesis and hypokalemia with a CACNA1S mutation confirmed via exome sequencing.

An atypical pattern IV was observed in the long exercise test, which is uncommon in PPHy-1.

Treatment with potassium supplementation and acetazolamide reduced attack frequency.

Abstract

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.

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