Morphometric approaches to perifascicular atrophy in muscle biopsy: do they help to diagnose polymyositis?

The sizes of muscle fibres in the peripheral and central parts of fascicles were compared in biopsies from patients with polymyositis/dermatomyositis, patients with slowly progressing muscular dystrophies and normal controls. Of three quantitative parameters tested, perifascicular atrophy factor gave the best discrimination between the patient groups. This factor is obtained by subtracting the atrophy factor of the peripheral fibres from that of the central ones. In polymyositis, the values tend to be negative as a result of atrophy affecting selectively the peripheral fibres, whereas in dystrophies the values are usually close to zero or positive. For the comparison between polymyositis and muscular dystrophy, the test based on perifascicular atrophy factor has an estimated sensitivity of 83% and a specificity of 65%. This quantitative method is thus able to increase sensitivity of the diagnosis of polymyositis over that attained by the subjective evaluation, even at the cost of a sizeable false-positive rate.