Background: Myasthenia Gravis (MG) is an autoimmune disease affecting 2 per 10,000(1). We present a case of undiagnosed MG which was unmasked following inadequate antagonism of neuromuscular blockade using sugammadex.
Case report: A 68-year old male presented with a 1 year history of intermittent dysphagia. Background history included atrial fibrillation. After investigation he was diagnosed with benign oesophageal stenosis and unsuccessfully treated with dilatation. MRI showed large anterior cervical osteophytes causing extrinsic pressure on the oesophagus. He was scheduled for an elective osteophytectomy.
A modified rapid sequence induction was performed with propofol 2mg/kg and rocuronium 1.2mg/kg. Anaesthesia was maintained with sevoflurane. The procedure was uneventful and neuromuscular blockade was reversed with sugammadex. In HDU, following apparent recovery, he complained of dysphagia and dysarthria with no immediate improvement.
Additional investigations were performed. CT and MRI brain were unremarkable. Barium swallow revealed features of bulbar palsy. Edrophonium testing was performed with positive results. There was complete recovery after a course of gammaglobulin and pyridostigmine. He was discharged on day 10 on pyridostigmine.
Discussion: Dysphagia is a common presentation of MG and initial misdiagnosis often occurs(2). Respiratory failure after general anaesthesia has been described in these cases, leading to the correct diagnosis. While sugammadex has been used in the perioperative management of MG, it is administered to patients taking concomitant cholinesterase inhibitors(3).
We propose that sugammadex resulted in incomplete return of neuromuscular function as it does not influence the concentration of acetylcholine at the motor end plate. An additional factor was use of steroids which can cause paradoxical weakness in 8-10%.
Learning Points: This case highlights the complexities of drug interaction at the neuromuscular junction and suggests that sugammadex alone may not be adequate for antagonism of neuromuscular blockade in patients not receiving cholinesterase inhibitors.
1. Phillips LH. The epidemiology of myasthenia gravis. Ann N Y Acad Sci. 2003;998:407
2. Khan OA, Campbell WW. Myasthenia gravis presenting as dysphagia: clinical considerations. Am J Gastroenterol. 1994;89(7):1083-1085
3. De Boer HD, Van Egmond J et al. Sugammadex in patients with myasthenia gravis. Anaesthesia. 2010;65:653