What is the differential for a patient with unilateral arm swelling, MRI with muscle edema, and markedly elevated CPK?  

The differential for focal myositis is broad, although many times no obvious etiology is revealed and in that case, it is considered to be idiopathic. Etiologies that need to be ruled out are: malignancy (usually confirmed by biopsy), infections (like mycobacteria, viruses, fungi; usually will have ...

Diabetic myonecrosis or infarction though rare should also be part of the differential. Atypical arm cases are reported, even though it’s common in the thigh and calf. Uncontrolled diabetes with renal, neural, and retinal involvement can be associated. MRI is the modality for diagnosis and tre...