Myositis associated with antimitochondrial autoantibodies presenting with early respiratory failure

Myositis associated with antimitochondrial M2 antibodies (AMA) is a distinct subtype of inflammatory myopathy characterized by axial muscle weakness and, occasionally, respiratory failure. This report highlights two cases involving patients presenting with severe respiratory failure while ambulant. Patient 1: An 82-year-old man was referred to our hospital for respiratory failure and truncal muscle weakness. Shortly after hospitalization, the patient succumbed to respiratory failure. Autopsy findings revealed inflammation predominantly affecting the respiratory muscles. Later, AMA were detected. Patient 2: A 69-year-old woman with a nine-year history of muscle weakness presented with chronic respiratory failure requiring mechanical ventilation. A biceps brachii muscle biopsy revealed mild necrosis. Corticosteroid therapy was successful in weaning the patient off ventilator support. Notably, both patients showed mild limb muscle weakness, contrasting the severity of their respiratory insufficiency. Myositis associated with AMA should be considered in the differential diagnosis of diseases causing respiratory failure in ambulatory patients.