Patient Case: Necrotizing Autoimmune Myopathy (NAM)
A 45-year-old female presents to the neurology clinic with a two-month history of progressive muscle weakness. She reports difficulty rising from a chair, climbing stairs, and lifting objects above her head. The weakness has worsened significantly over the past few weeks, but she denies muscle pain. She also experiences mild fatigue but no joint pain, skin rash, or sensory changes.
Medical History & Social Background
• Medical history: Hyperlipidemia (on atorvastatin for six months), mild hypertension.
• Family history: No known neuromuscular or autoimmune disorders.
• Occupation: Office worker, struggling with daily activities.
• Social history: Non-smoker, no history of alcohol or drug use.
Physical Examination
• Neuromuscular:
√. Symmetric proximal muscle weakness (shoulders, hip flexors).
√. No muscle atrophy or fasciculations.
√. Normal deep tendon reflexes and sensation.
• Cranial nerves: Intact; no facial or bulbar weakness.
• Cardiopulmonary: Normal heart and lung sounds.
Laboratory & Diagnostic Findings
• Creatine kinase (CK): Markedly elevated (12,000 U/L, normal <200 U/L).
• Aldolase, AST, ALT: Elevated.
• Autoantibody panel:
• Anti-HMGCR antibody: Positive (suggestive of statin-associated NAM).
• Anti-SRP antibody: Negative.
• Electromyography (EMG): Myopathic changes with irritability.
• Muscle biopsy:
√. Scattered muscle fiber necrosis without significant lymphocytic inflammation, confirming necrotizing autoimmune myopathy (NAM).
• Statin discontinuation: No improvement in weakness after four weeks.
Diagnosis
The combination of proximal muscle weakness, significantly elevated CK, anti-HMGCR positivity, and muscle biopsy findings confirms a diagnosis of necrotizing autoimmune myopathy (NAM), likely statin-induced.
Management Plan
1. Immediate treatment
• High-dose corticosteroids (prednisone 1 mg/kg/day).
• Discontinue atorvastatin permanently.
2. Immunosuppressive therapy (for steroid-sparing and long-term control)
• Methotrexate or azathioprine as first-line agents.
• Intravenous immunoglobulin (IVIG) or rituximab if refractory disease.
3. Monitoring & Long-Term Care
• Regular CK levels and muscle strength assessments.
• Liver function monitoring due to steroid and immunosuppressive therapy.
• Physical therapy to maintain mobility and prevent muscle wasting.
Challenges & Considerations
• NAM often requires prolonged immunosuppressive therapy.
• Patients with anti-HMGCR positivity may not recover fully even after statin discontinuation.
• Severe cases can progress to respiratory muscle weakness or cardiac involvement.
Prognosis
With early immunosuppressive treatment, most patients improve, but some may develop chronic muscle weakness. Long-term therapy and monitoring are necessary to prevent relapses.
A) Polymyositis
B) Necrotizing autoimmune myopathy (NAM)
C) Dermatomyositis
D) Myasthenia gravis
A) Low creatine kinase (CK) levels
B) Positive anti-HMGCR or anti-SRP antibodies
C) Positive anti-Jo-1 antibody
D) Normal muscle biopsy findings
A) High-dose corticosteroids
B) Colchicine
C) Acetylcholinesterase inhibitors
D) Hydroxychloroquine
A) Presence of rimmed vacuoles on muscle biopsy
B) Presence of significant lymphocytic inflammation on biopsy
C) Muscle fiber necrosis without prominent inflammation on biopsy
D) Positive anti-dsDNA antibodies
