816 - Challenges in Managing Anti-HMGCR Necrotizing Myopathy: A Case of Progressive Proximal Muscle Weakness Requiring Intensive Immunotherapy

Case Diagnosis: Anti-HMGCR Necrotizing Myopathy

Case Description: 58 year old male with history of hyperlipidemia presented with progressive proximal muscle weakness, weight loss (27lb), and bitemporal wasting over six weeks. Laboratory results were significant for elevated creatine kinase (CK) at 26,613 IU/L, and transaminitis (AST: 665 IU/L, ALT: 790 IU/L). Patient’s statin therapy was discontinued six weeks prior to presentation. Muscle biopsy revealed severe chronic myopathy with scattered necrotic fibers. Testing for anti-HMGCR IgG antibodies was positive. Patient was treated with intravenous steroids and IVIG then transferred to acute rehabilitation. Patient’s proximal muscle strength stagnated and CK levels plateaued at 6,000 IU/L. Due to persistent and insufficient control of proximal muscle weakness in acute rehab, patient was discharged for further medical management, including additional course of IVIG.

Discussions: This case exemplifies the complex nature of anti-HMGCR necrotizing myopathy, a rare but severe autoimmune condition. The patient's persistent proximal muscle weakness and elevated CK levels despite initial treatment highlight the necessity for a high index of suspicion and aggressive management. The elevated CK levels and severe necrotic findings on muscle biopsy are consistent with necrotizing autoimmune myopathy, where ongoing muscle damage despite statin discontinuation can occur. The clinical course illustrates the necessity of repeated immunosuppressive therapies, such as additional IVIG, when initial treatments do not achieve control.

Conclusions: Anti-HMGCR necrotizing myopathy results in challenges that require attentive monitoring and robust treatment approaches. Initial treatments may not suffice, as demonstrated by the patient’s persistent weakness and elevated CK levels despite standard therapies. Early identification and management are critical to optimizing patient outcomes. Considering the complexities involved in achieving the patient’s disease control, anti-HMGCR requires continuous assessment and adjustment of treatment plans to enhance outcomes.