Approach to myopathies

This chapter provides guidance in how to approach a patient with a suspected myopathy and should in most cases lead to a diagnosis or at least a diagnostic class of myopathy. This textbook has chapters covering all but the rarest types of myopathies and can provide further direction on the workup of specific myopathies. Each of the diagnostic steps-namely, the clinical evaluation, EMG, biopsy, and histological interpretation-involves many features which can be suggestive of certain myopathies, without being definitively diagnostic. To capture and synthesize all the information from each diagnostic step, the workup is ideally performed by the same neuromuscular physician who can perform all three steps. At many institutions this is not possible, and when a team of physicians is used for the workup, then close communication between the neurologist, electromyographer, surgeon, and pathologist is critical. Problems will arise if the referring and performing physicians do not know what questions can be answered by the EMG or how EMG results might shift the odds of diseases in the differential. Likewise the muscle biopsy needs to be performed with knowledge of what muscles were studied by EMG and which muscles will provide the most histological information. The muscle tissue samples need to be big enough and handled appropriately to allow for any preconceived testing. Lastly, the clinical information is critical for the correct interpretation of the muscle histology. When integrated with all the relevant clinical information, the evaluation of muscle histology is more likely to yield a correct diagnosis.