Muscle weakness and atrophy-clinical and laboratory evaluation.

A thorough family history, the age at the time of onset and detailed information regarding the rate, mode of progression and distribution of weakness is needed for evaluation of patients with weakness and atrophy. Associated findings such as dermal lesions, tenderness, myotonia and fasciculations should also be noted.The major diagnostically useful laboratory tests are electromyography, nerve conduction, serum enzyme levels and muscle biopsy.Each clinical and laboratory finding should be categorized in terms of its neuro-anatomical origin, since weakness may result from disturbances in the corticospinal pathways, the lower motor neuron, the myoneural junction and the muscle.