Generalized intramuscular granulocytic sarcoma mimicking polymyositis.

We report a case of granulocytic sarcoma exclusively manifesting as diffuse intramuscular infiltration of the proximal upper and lower limb girdle and the torso muscles in a patient with previous history of acute myelogenous leukemia 5a. Whole-body CT showed widespread distribution of ill-defined intramuscular, homogeneously enhancing lesions. On whole-body MRI, lesions were homogeneously hyperintense on fat saturated T2-weighted images, isointense on T1-weighted images and strongly enhancing after intravenous gadolinium contrast administration. Histopathology revealed muscular infiltration of blast cells with identical immunochemistry to the initial manifestation of leukemia, diagnostic for an extramedullary relapse manifesting as granulocytic sarcoma. CT and MRI characteristics of this previously undocumented manifestation of granulocytic sarcoma should assist in the identification of such cases.