A man in his late 70s presented with 1 week of progressive chest and muscle pain, generalized weakness, and fatigue. He received 1 infusion of Pembrolizumab 3 weeks prior as adjuvant immunotherapy for stage IIb malignant melanoma after undergoing wide local surgical excision. He was started on oral prednisone (1 mg/kg) daily for Pembrolizumab-induced myositis. Symptoms progressed to include severe dyspnea, dysphagia, and eyelid ptosis requiring ventilatory support. He was treated with 5 sessions of plasma exchange, pyridostigmine up to 90 mg three times daily, and IV methylprednisolone. He improved and was taken off BiPap but soon after developed pneumonia with septic shock and subsequent worsening of respiratory function. He received 2 days of IVIG but required intubation, tracheostomy, antibiotics, vasopressors, CRRT, and PEG tube placement. He underwent 3 plasma exchanges before developing anemia and thrombocytopenia requiring transfusion.
Serologic studies ultimately confirmed MG and anti-SSA myositis positive acetylcholine binding antibody at 2.84 (reference range 0.00-0.24), positive acetylcholine modulating antibody at 58% (reference range 0-45%). Myositis panel revealed an elevated anti-SS-A 52kD antibody IgG of 31 (reference range <20).
The patient was discharged in a stable condition to a long-term care facility after a 37-day admission on prednisone and pyridostigmine. Patient was doing well in clinic after discharge.