Primary hypokalemic periodic paralysis with sinus bradycardia: a case report and review of literature

Abstract

Hypokalemic periodic paralysis (HPP) is a rare autosomal dominant disorder caused by mutations affecting skeletal muscle ion channels, most commonly CACNA1S or SCN4A. It manifests as recurrent episodes of flaccid paralysis associated with low serum potassium levels, often precipitated by rest after exertion, high-carbohydrate intake, or intercurrent illness. Although the condition typically presents during adolescence, diagnosis is often delayed due to its episodic nature and overlap with other causes of acute weakness. The estimated incidence is 1:100,000. HPP with cardiac arrhythmias have been reported but sinus bradycardia is not reported so far. Hence, we present a rare case of primary HPP type 2 with sinus bradycardia and a pathogenic genetic variant. A 16-year-old male child born to third-degree consanguineous parents, presented to the emergency department with an acute episode of fever, vomiting, headache, generalized weakness with difficulty in getting up or standing since waking up that morning. The weakness initially involved the lower limbs and then progressed to the upper limbs within few hours. Electrocardiogram showed sinus bradycardia with prominent U waves. Serum potassium was 1.2 mmol/l with sodium, magnesium and calcium within normal limits. The paralysis and ECG abnormality became normal following replacement of potassium. There was a similar history in father and paternal uncle. Genetic study detected a heterozygous missense variant in exon 12 of the SCN4A gene (chr17: g.63959279G>C; Depth: 85x) that results in the amino acid substitution of glycine for arginine at codon 669 (p.Arg669Gly; ENST00000435607.3) causative of HPP, type 2. HPP is a rare neuromuscular disease that can present with cardiac arrhythmias. We present a case of primary HPP type 2 with sinus bradycardia which resolved spontaneously with potassium supplementation.