Presentation
Bilateral lower extremity weakness, particularly proximally. History of hyperlipidemia treated with statins. No history of trauma or overexertion. No rashes on physical exam. Blood tests showed markedly elevated serum creatine kinase level.
Patient Data
Axial and coronal T1 and T2 fat sat MRI sequences of the bilateral thighs without IV contrast. These are wide field-of-view images obtained according to the myositis protocol at our institution. The images show edema like signal in the bilateral thigh musculature, most pronounced in the medial and posterior compartments. No fascial or subcutaneous edema is seen. There is minimal generalized muscle atrophy in the bilateral thighs.
CT of the pelvis shows moderate atrophy of the bilateral gluteus maximus muscles in a symmetric manner.
Case Discussion
Immune mediated necrotizing myopathy (IMNM), along with dermatomyositis, polymyositis, antisynthetase syndrome, and inclusion body myositis constitute the major types of idiopathic inflammatory myopathies ². Histological and serological analysis are often required to differentiate IMNM from other idiopathic inflammatory myopathies. Treatment of IMNM can be challenging and involves immunosuppressive therapy.
In the case shown, involvement of the bilateral gluteal muscles and bilateral medial and posterior compartment muscles of the thighs on imaging raised suspicion for IMNM. Muscle biopsy from the right lateral thigh was consistent with necrotizing myopathy. Anti-HMGCR antibody was positive. The patient's symptoms improved after cessation of statins and after treatment with steroids.
Case co-author: Eva Napierkowski (Loyola University)
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