All-trans retinoic acid-induced inflammatory myositis in a patient with acute promyelocytic leukemia.

All-trans retinoic acid (ATRA), a component of standard therapy for acute promyelocytic leukemia (APL), is associated with potentially serious but treatable adverse effects involving numerous organ systems, including rare skeletal muscle involvement. Only a handful of cases of ATRA-induced myositis in children have been reported, and none in the radiology literature. We present such a case in a 15-year-old boy with APL, where recognition of imaging findings played a crucial role in making the diagnosis and facilitated prompt, effective treatment.