A 73-year-old male presented with a one-year history of progressive flaccid paraparesis, dysphagia, and loss of independent ambulation. His medical history was notable for chronic statin therapy at 80 mg daily over the past four years and coronary stent placement for aortic stenosis. Neurological examination revealed symmetric lower-limb weakness without sensory or sphincter involvement, absent reflexes, and no upper motor neuron signs.

Electromyography showed severe inflammatory myopathy with denervation potentials and rapid recruitment of small motor units. Quadriceps ultrasound revealed structural abnormalities. Laboratory evaluation revealed CK 11,600 U/L and myoglobin 3,100 ng/mL, with positive anti-HMG-CoA reductase antibodies, confirming SINAM.

Initial treatment with intravenous fluids and IVIG (400 mg/kg/day × 5 days) resulted in significant improvement (CK 3,117 U/L, myoglobin 400 ng/mL). However, relapse occurred with recurrent weakness, and CK 5,617 U/L. High-dose corticosteroids pulses were ineffective. A second IVIG course combined with azathioprine titrated to 150 mg/day achieved approximately 60% functional recovery.