Immune-mediated Necrotizing Myopathy With Increased Creatine Phosphokinase and Positive Signal Recognition Particle: A Case Report

Background: Knowledge about Immune-Mediated Necrotizing Myopathy (IMNM) has received significantly attention in recent years. In this study, we report a rare case of IMNM with increased Creatine Phosphokinase (CPK) and positive Signal Recognition Particle (SRP). Clinical Presentation and Intervention: The case was a 67-year-old male patient referred to Firozgar hospital affiliated to the Iran University of Medical Science, Tehran, Iran in June 2018 with a chief complaint of pain in the proximal lower extremity. According to Medical Research Council Scale for muscle strength, the motor function of proximal upper extremities was 4/5 and for the proximal of the lower extremities, it was 3/5. Laboratory findings showed an increase in CPK, CK-MB, lactate dehydrogenase, creatinine, alanine aminotransferase, aspartate aminotransferase and aldolase levels. Six days after admission, autoantibody test was requested which showed positive SRP. In muscle biopsy, the myopathic atrophy with multiple necrotic and many degenerative/regenerative fibers was associated with mild endomysial fibrosis, and no inflammation was observed. Two g/kg dose of Intravenous Immunoglobulin (IVIG) was administrated after diagnosis of IMNM. Prednisone 50 mg/day orally, calcium vitamin D daily, pantoprazole 40 mg/day, physiotherapy, and occupational therapy were administrated for after discharge. Conclusion: Reporting a case of anti-SRP associated IMNM and reviewing its pathophysiology, diagnosis and treatment options can help increase the physicians’ knowledge of this rare and debilitating condition.