Atrophy and hyporeflexia are very late findings in most patients with myopathy. The early presence of these findings usually implicates neuropathies. Significant muscle pain and tenderness without weakness should prompt physicians to consider other causes. Acuity of symptom onset aids in diagnosis. Weakness progressing over hours suggests a toxic etiology or one of episodic paralyses.
Weakness developing over days suggests acute dermatomyositis or rhabdomyolysis.
Symptoms of the patient indicate which muscle groups are involved. Objective weakness, usually in a symmetric distribution of proximal muscle groups is observed. Muscle tenderness is rare. Fever, particularly with pyomyositis or polymyositis may occur. Muscle mass should be normal.