Pathology of eosinophilic fasciitis and its relation to polymyositis

The anatomical substrate of eosinophilic fasciitis (EF) was studied in 15 muscle biopsy specimens of this disease, six of which included the dermis and subcutaneous tissue. As controls, 94 postmortem muscle specimens from patients dying of non-muscular diseases were used. Of these 94 specimens, 22 (23.4%) showed practically no deep fascia and 72 specimens showed a single dense bundle of collagen with no distinction between deep fascia and epimysium. The 15 specimens of EF showed thickening and inflammatory infiltration of varying degrees in the deep fascia, epimysium, perimysium, endomysium and also in muscle. We conclude that the anatomical substrate of EF is not confined to the deep fascia, but involves other structures including mysia and muscle itself. Most reported cases of EF in the literature do not even describe muscle. A comparative study of 15 biopsy specimens of polymyositis and dermatomyositis with those of EF revealed only quantitative differences in the histopathological changes of muscle and mysia, inflammatory infiltrate and eosinophilia. We suggest that the diseases are more closely related than previously recognized.