Carbon monoxide poisoning-induced myositis

Introduction: Carbon monoxide (CO) poisoning is common and potentially life-threatening. While neurological and systemic complications are well recognized, muscle involvement, such as myositis, is rare. Case presentation: We report a 38-year-old man with no prior medical history who suffered CO poisoning after inhaling motorcycle exhaust in a closed garage, presenting in coma. He received intensive care and hyperbaric oxygen therapy. One month later, he experienced persistent right thigh myalgia and quadriceps weakness. Laboratory tests were normal, but magnetic resonance imaging (MRI) revealed T2 and fat saturation hypersignal with gadolinium enhancement in the vastus lateralis over 9 cm, consistent with active myositis. Electromyography and X-ray were unremarkable. Other causes, including drug-induced myositis, inflammatory myopathies, and endocrine disorders, were excluded. Treatment with anti-inflammatory medications and rest alleviated pain, though mild weakness persisted. Follow-up MRI at 4 months showed regression of the lesions. Discussion: CO-induced myositis results from tissue hypoxia via the high affinity of CO for myoglobin and inhibition of cytochrome oxidases, sometimes exacerbated by compression during coma. Diagnosis relies on clinical history, elevated muscle enzymes, and MRI, which provides a non-invasive alternative to biopsy. Conclusion: Myositis is a rare complication of CO poisoning. Early recognition and hyperbaric oxygen therapy are essential, with MRI serving as a valuable diagnostic tool to guide management and monitor recovery.