Antipsychotic-Associated Muscle Disorders

Clinical Presentation and Diagnosis

• Miosite verdadeira presents with progressive proximal muscle weakness, persistent elevation of CPK, electromyographic changes with fibrillation potentials and myopathic pattern, and diffuse muscle edema on magnetic resonance imaging 1, 2
• The American College of Rheumatology recommends differentiating between pain and true weakness, as miosite causes proximal weakness (difficulty rising, climbing stairs, lifting arms), not just pain 2
• The European Society of Cardiology suggests measuring CPK and repeating in 3-5 days, with persistent and marked elevation (>10x normal) suggesting necrotizing myopathy, not an antipsychotic effect 2, 3
• The American Academy of Neurology recommends requesting specific myositis autoantibodies (anti-Jo-1, anti-Mi-2, anti-MDA5) if elevated CPK persists 2

Differential Diagnosis

• Other causes of muscle weakness, such as viral infections (benign self-limiting viral myositis), concomitant medications (statins are much more likely), and autoimmune diseases, should be considered 4, 2