Abstract Introduction Triple M syndrome—the combination of myocarditis, myositis, and myasthenia gravis—is a rare but severe immune-related adverse event associated with immune checkpoint inhibitors (ICIs) such as pembrolizumab. This syndrome carries a high risk of respiratory failure, arrhythmias, and death, with over two-thirds of reported cases requiring intensive care support. Case Description A 57-year-old woman with diabetes mellitus and metastatic breast cancer involving bone, liver, and leptomeninges presented with progressive diplopia, ptosis, exertional dyspnea, hoarseness, and dysphagia approximately 20 days after initiating pembrolizumab and paclitaxel. Laboratory evaluation revealed elevated troponin, creatine kinase, ESR, and CRP. She was diagnosed with pembrolizumab-induced Triple M syndrome. Treatment with dexamethasone and pyridostigmine led to improvement in ocular symptoms; however, worsening respiratory effort, declining negative inspiratory force, and reduced vital capacity prompted ICU transfer for airway monitoring and initiation of plasmapheresis. She required only low-flow nasal cannula oxygen for respiratory effort and did not require mechanical ventilation. After two sessions of plasma exchange, her respiratory function and exertional tolerance gradually improved. She was discharged following her fifth session on dexamethasone, pyridostigmine, and long-acting insulin for corticosteroid-induced hyperglycemia. Discussion With the increasing use of ICIs, awareness of immune-mediated neuromuscular and cardiac complications is essential. Triple M syndrome is associated with high morbidity and mortality, with up to 40% of patients requiring mechanical ventilation. Treatment options include corticosteroids (at variable doses), IVIG, plasmapheresis, and, in refractory cases, advanced immunosuppressants such as rituximab or abatacept. Clinicians should be alert to transient symptom worsening after steroid initiation. Early recognition and a multidisciplinary approach involving neurology, oncology, and critical care are vital to optimizing outcomes in this life-threatening complication of immunotherapy. This abstract is funded by: None
Kujundzic et al. (Fri,) studied this question.
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