McArdle Disease: A Rare Cause of Rhabdomyolysis

Background: Rhabdomyolysis may be asymptomatic or cause potentially life-threatening renal failure. It is most commonly caused by trauma, viral infections or drugs, but it is important to consider less frequent aetiologies, such as metabolic diseases which may require a high level of suspicion.

Objective: We present a case of rhabdomyolysis secondary to McArdle disease to demonstrate the importance of a detailed clinical history in identifying a rare cause of this common condition.

Method - Case report: A 17 year-old male came to the emergency department with non-specific skin lesions in the previous two weeks, followed by dark urine for over one week. He denied trauma, muscle cramps or strenuous exercise. Upon further questioning, he described mild muscle fatigue in the preceding months, mostly at the beginning of exercise, with recovery after resting, that motivated him to abandon sports. There was no family history of neuromuscular disease, but his parents are second degree cousins.

Physical examination revealed mild shoulder and pelvic girdle muscle wasting and painful thigh muscles.

Laboratory evaluation showed significant elevation of creatine kinase, transaminases and LDH and urinalysis showed myoglobinuria. Infectious, drug-related, endocrine and inflammatory causes were not identified. Metabolic investigation included an ischemic forearm test, which was suggestive of a glycogenolysis defect. Genetic testing confirmed a homozygous mutation in the PYGM gene compatible with McArdle disease.

Conclusion: McArdle disease is an autosomal recessive metabolic myopathy caused by an inherited deficit of myophosphorylase, which affects the use of glucose by skeletal muscle cells, predisposing them to injury. Clinical presentation is variable and may include rhabdomyolysis.

Early diagnosis permits the implementation of simple strategies that may prevent further episodes of rhabdomyolysis and improve quality of life.