1020 - Statin-Induced Necrotizing Autoimmune Myopathy (SINAM) on Chronic Statin Therapy

MRI T-spine showed bilateral trapezius and rhomboid edema, muscle biopsy showed severe necrotizing myopathy, and HMG-CoA reductase antibody IgG was elevated at 197 (ref range 0-19), supporting the diagnosis of SINAM.

Case Description:

53-year-old male with PMH of DMII, HLD on Atorvastatin 40mg for five years, morbid obesity, and recent coccyx fracture and immobility secondary to fall one month prior presented with a chief complaint of generalized body weakness. He had markedly decreased strength with hip flexion/extension and shoulder abduction and forward flexion bilaterally, with fully intact grip strength, dorsiflexion, and plantarflexion. His sensory exam and DTRs were normal. Initial creatine kinase level was 17,000 with transaminitis. CK plateaued at 9,000 after five days of fluids. The patient was empirically started on methylprednisolone just before the diagnosis of statin-induced necrotizing autoimmune myopathy (SINAM) was made, which greatly helped with his weakness.  He was subsequently started on IVIG and had excellent improvement with CK decreasing to 3,000 before being discharged to ARF.

Discussions:

SINAM occurs in 2 to 3 out of every 100,000 persons treated with statins, and can occur at any time after beginning therapy, even after many years. A systematic review found a mean duration of statin use prior to myopathy symptom onset of 40.48 months, which correlates well with our patient’s five year total use. Findings that strengthen the diagnosis of SINAM include CK elevations 10x the upper limit of normal, an elevated HMG-CoA reductase antibody level, and necrotizing myopathy on muscle biopsy. The treatment of SINAM typically involves discontinuation of the statin and initiation of immunosuppressive therapy. Steroids (typically oral prednisone 1mg/kg/day) and IVIG are the mainstays.

Conclusions:

This case highlights the challenges in diagnosing SINAM, as the clinical presentation may initially overlap with other conditions including trauma and prolonged immobility.