[Exercise-intolerance and exercise-induced rhabdomyolisis: etiology and diagnosis]

Exercise intolerance, sometimes complicated by rhabdomyolysis is a frequent complaint of patients consulting in neuromuscular centers. It may be the main clinical manifestation of many metabolic myopathies and muscular dystrophies. The first step of diagnosis relies on the performance of in vivo metabolism investigations: forearm or bicycle ergometer exercise tests, phosphorus nuclear magnetic resonance spectroscopy. A few enzymatic defects may be directly assessed on blood samplings, in particular carnitine palmitoyltransferase deficiency; but muscle biopsy is necessary in most cases in order to precise the etiology. When CK levels are elevated at rest, a muscle CT scan should be performed in order to detect muscles fatty replacement suggestive of a muscular dystrophy; this diagnosis will be confirmed with immunohistochemical and western-blot analysis of muscle proteins. We present a description of the main metabolic myopathies manifesting by exercise intolerance with an overview of clinical and laboratory evaluation leading to diagnosis. Differential diagnosis are also discussed.