DOI: 10.12890/2025_005849

When fatigue hides a metabolic myopathy: a case report of McArdle disease with molecular diagnosis

Authors

  • Beatriz Teixeira Lima Internal Medicine, Unidade Local de Saúde do Baixo Mondego, Figueira da Foz, Portugal 0000-0002-8836-775X
  • André S. Carvalho Internal Medicine, Unidade Local de Saúde do Baixo Mondego, Figueira da Foz, Portugal 0000-0003-4054-0100
  • Ana Catarina Camarneiro Internal Medicine, Unidade Local de Saúde do Baixo Mondego, Figueira da Foz, Portugal 0000-0003-3106-1511
  • Bárbara A.M. Baptista Internal Medicine, Unidade Local de Saúde do Baixo Mondego, Figueira da Foz, Portugal 0000-0002-1914-2354
  • Ricardo Rocha Gomes Internal Medicine, Unidade Local de Saúde do Baixo Mondego, Figueira da Foz, Portugal 0000-0002-4142-8850
  • Marta Isabel Brás Internal Medicine, Hospital CUF Coimbra, Coimbra, Portugal 0000-0002-1032-010X
  • Susana Magalhães Internal Medicine, Unidade Local de Saúde do Baixo Mondego, Figueira da Foz, Portugal 0000-0002-0644-664X

abeatrizrtlima@gmail.com

Keywords

Muscle fatigue, creatine kinase, muscle phosphorylase, glycogen storage disease, McArdle disease

Abstract

McArdle disease, or glycogen storage disease type V, is a rare inherited metabolic myopathy caused by mutations in the PYGM gene, resulting in deficiency of the enzyme myophosphorylase. Patients usually present with lifelong exercise-induced fatigue, muscle pain, and sometimes rhabdomyolysis, but the condition is underdiagnosed due to its nonspecific manifestations. This case is distinctive because it documents molecularly confirmed McArdle disease in a woman with persistently elevated creatine kinase and a suggestive family history, underlining the importance of clinical suspicion, timely genetic testing, and appropriate counselling.
A 35-year-old woman reported lifelong myalgia and easy fatigability. Her past history included recurrent migraines and use of a progestogen-only contraceptive. One sister, aged 21, had similar symptoms, while her other sister and parents were healthy. Physical examination was unremarkable. Laboratory tests showed an isolated elevation of creatine kinase (1,504 U/l). Genetic analysis revealed the PYGM c.148C>T, p.(Arg50*) variant in apparent homozygosity, a rare mutation transmitted in heterozygosity. At follow-up she was 30 weeks pregnant and was referred, along with her symptomatic sister, to a genetic consultation. Behavioural guidance focused on regular moderate exercise and symptom management.
McArdle disease is underdiagnosed because its symptoms are often misinterpreted as poor physical fitness. This case highlights that early recognition, and molecular confirmation can avoid unnecessary invasive tests and provide clarity in patients with chronic exertional intolerance. The identification of a rare PYGM variant further emphasizes the importance of genetic counselling, which enables family screening and informed reproductive planning. Timely recognition and tailored management are essential for improving patient quality of life.

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References

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Published

2025-10-06

Issue

Vol. 12 No. 11 (2025)

Categories

How to Cite

1.
Teixeira Lima B, S. Carvalho A, Camarneiro AC, Baptista BA, Rocha Gomes R, Brás MI, et al. When fatigue hides a metabolic myopathy: a case report of McArdle disease with molecular diagnosis. EJCRIM [Internet]. 2025 Oct. 6 [cited 2026 Nov. 3];12(11). Available from: https://ejcrim.com/index.php/ejcrim/article/view/5849