The perifascicular atrophy factor. An aid in the histological diagnosis of polymyositis.

19 biopsies of polymyositis patients were compared with 19 matched controls. The presence of smaller fibres in the periphery of the fascicles has been analyzed quantitatively using a perifascicular atrophy factor. The thinner fibres are multiplied by a factor from 1-4, considering their significance for the diagnosis of fibre atrophy. The value obtained with this method from centrally located fibres as related to the value from peripherally located ones is called the perifascicular atrophy factor. If this is less than -300 a myopathy of the group of the polymyositis/dermatomyositis can be assumed. 47 per cent of dermatomyositis biopsies and none of the controls were below this range