Myasthenia gravis and a rare complication of chemotherapy

In February, a 49-year-old self-employed builder developed MG and was subsequently found to have invasive thymoma. This was incompletely excised. The surgical procedure was complicated by left phrenic nerve palsy.

In May, the patient commenced his first cycle of chemotherapy, which was to comprise doxorubicin 50 mg/m2 Day 1, cisplatin 100 mg/m2 Day 1 and etoposide 120 mg/m2 Days 1, 3 and 5, with dexamethasone 20 mg, ondansetron 8 mg and metoclopramide 10 mg administered before chemotherapy to control nausea. His MG had been well controlled on pyridostigmine 60 mg twice daily. However, within 24 hours of the first dose of chemotherapy, he developed a severe myasthenic crisis with respiratory failure requiring intubation. This was managed with dexamethasone 8 mg daily and plasmapheresis, and was thought to be due to the high-dose dexamethasone given prior to chemotherapy. In addition, he had developed a chest infection a couple of days before starting chemotherapy, which may have contributed to the respiratory failure. A methicillin-sensitive Staphyloccus aureus was isolated from sputum cultures. This was managed upon hospitalisation with intravenous ceftriaxone 1 g daily for 7 days.

In June, the patient received his second cycle of chemotherapy, this time without dexamethasone. Within several hours, he developed increasing breathlessness with bulbar dysfunction and generalised weakness. Despite treatment with steroids and intravenous neostigmine, his respiratory state continued to deteriorate, necessitating intubation and subsequent plasmapheresis.

No further cycles of chemotherapy were administered. A restaging computed tomography scan at the time revealed minimal residual tumour and mediastinal lymphadenopathy. In August, he completed a course of mediastinal radiotherapy that was complicated by mild radiation pneumonitis.