Obtain a thorough evaluation of
motor function and exercise tolerance. Inquire about previous complications
(cardiac, respiratory, other), especially those following surgeries. Seek
any familial history of muscle weakness. Evaluate pulmonary function test
(forced vital capacity [FVC], peak expiratory flow rate [PEFR], forced
expiratory volume in 1 second [FEV1], FEV1/FVC, arterial blood gas
analysis, chest radiographs) and cardiac function (ECG, echocardiography,
and, if necessary, dobutamine stress echocardiography or radionuclide
imaging). Plasma levels of creatine phosphokinase, serum
glutamic-oxaloacetic transferase, lactate dehydrogenase, Na, and K. Avoid
elective surgery if cardiac and/or respiratory function is significantly
compromised (ventricular ejection fraction <0.5, FVC <25%, PEFR <30%).
Inquire about corticosteroids or other immunosuppressive agents; some
patients may be treated with these agents even though they are unsuccessful
in controlling the disease.