SHM Converge Scientific Abstract ePoster Gallery-Negative Antibodies, Positive Damage: A Case of Seronegative Immune-Mediated Necrotizing Myositis

Pdf Summary

This case describes a 56-year-old man with ESRD on hemodialysis, diabetes, hypertension, dyslipidemia treated with atorvastatin, and prior stroke who developed two months of progressive generalized weakness, dysphagia, polyarthralgia, and recurrent falls. Weakness began in the left leg and spread to the right leg, arms, and trunk. Exam showed marked bilateral proximal muscle weakness and tenderness of the thighs and calves, without skin findings.<br /><br />Laboratory studies revealed severe muscle injury and inflammation, with creatine kinase of 61,334 U/L, ESR 130 mm/hr, and CRP 179 mg/L. ANA was weakly positive at 1:80, but the extended myositis panel, including anti-HMGCR and anti-SRP antibodies, was negative. MRI of the thighs showed diffuse intramuscular edema, while brain imaging showed only chronic changes and cervical spine MRI showed degenerative stenosis that did not explain the full presentation.<br /><br />A vastus lateralis biopsy demonstrated severe myopathy with necrotic fibers and minimal inflammation, consistent with autoimmune necrotizing myositis. The differential included statin-associated muscle toxicity versus inflammatory myopathy, so atorvastatin was stopped and malignancy screening was performed, without evidence of cancer. Because of strong suspicion for immune-mediated necrotizing myositis (IMNM), he received pulse-dose corticosteroids and IVIG, leading to a rapid fall in CK and clinical improvement. He was later tapered on steroids and continued monthly IVIG, ultimately discharged on IVIG monotherapy.<br /><br />The report emphasizes that seronegative IMNM can occur despite negative autoantibodies and may account for up to 40% of cases. In patients with progressive proximal weakness and high CK, muscle biopsy is essential when serologies are negative. Early treatment with corticosteroids and/or IVIG improves outcomes and is important because seronegative IMNM may carry increased risks of malignancy and cardiac involvement.

Asset Subtitle

Bonnie Cruser

Meta Tag

Author List Adetoun Adeyemi, Almeera Lateef, Anushua Bhattacharya, Ariella Tsfoni, Bonnie Cruser, Jacqueline Baikovitz, Ketino Kobaidze, Prateek Gandiga

Category Clinical Vignettes

Concept Immune-Mediated Necrotizing Myopathy

Concept Proximal Muscle Weakness

Concept Creatine Kinase

Concept Muscle Biopsy

Concept Necrotic Muscle Fibers

Distinguished Non-Finalist

Presenter Organization Division of Hospital Medicine at Emory University Hospital Midtown, Atlanta, GA

Presenting Author Bonnie Cruser

Track Adult

Keywords

immune-mediated necrotizing myositis

seronegative IMNM

rhabdomyolysis

proximal muscle weakness

elevated creatine kinase

muscle biopsy

atorvastatin

hemodialysis

IVIG therapy

corticosteroids

Immune-Mediated Necrotizing Myopathy

Proximal Muscle Weakness

Creatine Kinase

Muscle Biopsy

Necrotic Muscle Fibers