G.P.5: Clinical profile of a 6-year old boy with Becker Muscular Dystrophy and asymptomatic rhabdomyolysis: A case report

Abstract

<i>Background:</i> There have been several reports in the literature of exercise-related muscle cramps and myoglobinuria, or asymptomatic myoglobinuria leading to a diagnosis of Becker Muscular Dystrophy (BMD). <i>Objective:</i> To present the complete clinical profile of a child with BMD with asymptomatic rhabdomyolysis, and to contribute to natural history data. <i>Case report:</i> MG is a 6 year old male referred with a dystrophinopathy. He had exercise-induced cramps in his legs and a tendency to toe-walk at age 4. CPK was 8100. He had an Xp21.1 gain-of-function mutation on chromosomal microarray, and an in-frame duplication of exons 17–25 of the dystrophin gene. His initial exam was normal with the exception of mild hypotonia and pronated feet. Muscle MRI of his pelvic and thigh muscles showed minimal fatty changes. Muscle biopsy showed mild dystrophic changes (some increased centrally located nuclei, perimysial fibrosis, minimal necrotic fibers, and minimal fibrofatty changes) with significantly decreased staining for dys3 antibody. Western blot analysis indicated between 20% and 100% of muscle dystrophin confirming BMD. At follow-up, he reported a single episode of dark urine the prior evening which spontaneously resolved, without cramps, pain, or fatigue. Examination was normal. Post-visit labs were notable for rhabdomyolysis (CPK 56 100, AST 930, ALT 675, myoglobin 555). Labs 1week later showed a persistently elevated myoglobin (537), baseline CPK (6182), AST (163), and ALT (332), and normal urinalysis. The patient remained asymptomatic, and was advised to continue aggressive hydration. <i>Conclusion:</i> Our case describes the complete clinical profile (including pathology, dystrophin status, and muscle MR) of a patient with BMD with an episode of asymptomatic rhabdomyolysis. This case highlights the need to appropriately screen children, to provide anticipatory guidance on monitoring and management of rhabdomyolysis to families, and provides natural history data on the disease.