Hypokalemic periodic paralysis: a 3-year follow-up study

Sonja Holm-Yildiz*, Thomas Krag, Nanna Witting, Britt Stævnsbo Pedersen, Tina Dysgaard, Louise Sloth, Jonas Pedersen, Rebecca Kjær, Linda Kannuberg, Julia Dahlqvist, Josefine de Stricker Borch, Tuva Solheim, Freja Fornander, Anne-Sofie Eisum, John Vissing

*Corresponding author for this work

Abstract

BACKGROUND AND OBJECTIVES: Primary hypokalemic periodic paralysis (HypoPP) is an inherited channelopathy most commonly caused by mutations in CACNA1S. HypoPP can present with different phenotypes: periodic paralysis (PP), permanent muscle weakness (PW), and mixed weakness (MW) with both periodic and permanent weakness. Little is known about the natural history of HypoPP.

METHODS: In this 3-year follow-up study, we used the MRC scale for manual muscle strength testing and whole-body muscle MRI (Mercuri score) to assess disease progression in individuals with HypoPP-causing mutations in CACNA1S.

RESULTS: We included 25 men (mean age 43 years, range 18-76 years) and 12 women (mean age 42 years, range 18-76 years). Two participants were asymptomatic, 21 had PP, 12 MW, and two PW. The median number of months between baseline and follow-up was 42 (range 26-52). Muscle strength declined in 11 patients during follow-up. Four of the patients with a decline in muscle strength had no attacks of paralysis during follow-up, and two of these patients had never had attacks of paralysis. Fat replacement of muscles increased in 27 patients during follow-up. Eight of the patients with increased fat replacement had no attacks of paralysis during follow-up, and two of these patients had never had attacks of paralysis.

DISCUSSION: The study demonstrates that HypoPP can be a progressive myopathy in both patients with and without attacks of paralysis.

Original languageEnglish
JournalJournal of Neurology
Pages (from-to)6057-6063
ISSN0340-5354
DOIs
Publication statusPublished - Dec 2023

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