Comparison of the Pathology of Fascia in Eosinophilic Myalgia Syndrome Patients and Idiopathic Eosinophilic Fasciitis

In the 1993 study, researchers examined the pathology of fascia in 21 biopsies from patients with Eosinophilic Myalgia Syndrome (EMS) and 8 from those with Idiopathic Eosinophilic Fasciitis (EF). They found that both conditions exhibited dermal and fascial mucin and dermal edema, but these features were more prevalent in EMS. Additionally, EMS was distinguished by dilated lymphatics, dermal and septal sclerosis, and macrophage-rich inflammation. Neural inflammation was present in 4 cases of EMS but absent in idiopathic EF. Despite the histopathological similarities, the differences observed could be attributed to variations in sampling and the small sample size. The nerve lesions in EMS may be caused by lymphocyte-macrophage inflammation or the effects of eosinophil neurotoxin and might not be an initial occurrence in the disease process.