These general diagnostic criteria appear to improve the sensitivity of the adult criteria. They need further assessment in prospective clinical and epidemiologic studies.

The risk for malignant disease is increased in biopsy-proven dermatomyositis and polymyositis and also appears to be increased in inclusion-body myositis.

Heterogeneous clinical features, tissue specificity, and absence of lactic acidosis or abnormal mitochondrial morphology in many patients have resulted in underdiagnosis of respiratory chain complex I deficiency.

Benign acute myositis is a syndrome of midchildhood that can be differentiated from more serious causes of walking difficulty by the presence of calf tenderness, normal power, intact tendon reflexes, and elevated creatine kinase. The gait patterns noted may minimize power generation of the calf muscles by splinting the ankles. Onset in childhood may reflect an age-related response to viral infection, and occurrence primarily in boys may reflect a genetic predisposition or an as-yet unknown metabolic defect.

There is significant ipsilateral quadriceps atrophy and weakness with 2A and 2B fibre atrophy preoperatively in patients with osteoarthritis of the hip with exacerbation and further atrophy of all three fibre types 5 days postoperatively. Postoperative follow up showed that the reduction in ipsilateral quadriceps muscle thickness persisted at 5 months despite physical rehabilitation. Patients did note significant improvement in pain postoperatively and improvement on functional assessment with the TUG test. Other therapeutic strategies may have to be developed to reverse disuse muscle atrophy.