Endoscopic Surgery “Unmasks” Undiagnosed Myasthenia Gravis

A patient who emerged from general anesthesia with upper and lower extremity weakness caused worry among his doctors that he might have a spinal cord injury. Instead, new-onset myasthenia gravis (MG) was diagnosed.

MG is an autoimmune disease that affects the neuromuscular junction (NMJ) and results in severe muscle weakness. The case, reported in OTO Open, shows how the drugs used during surgical operations may have the effect of reducing the efficiency of neuromuscular transmission such that undiagnosed MG becomes more evident.

The case report authors said the case began when a 60-year-old man underwent an otherwise unremarkable procedure to endoscopically repair a Zenker’s diverticulum. The patient was put under anesthesia. He was given ampicillin and sulbactam prior to the incision; lidocaine, propofol, and remifentanil (Ultiva) for induction and maintenance of anesthesia; and rocuronium (Zemuron), ketorolac, ondansetron (Zofran), dexamethasone, and neostigmine and glycopyrrolate to reverse the neuromuscular blockade (NMB).

At first, all seemed well following the procedure.

“Emergence from anesthesia, return of spontaneous ventilation, and extubation was uneventful,” the authors said. “However, during recovery, the patient began to complain of new-onset upper and lower extremity weakness.”

The patient could not walk without 2-person assistance, although he had no sensory deficits and no difficulty urinating, the authors said.

“The clinical features were suggestive of acute cervical spinal cord injury, or central cord syndrome, raising the concern that this devastating complication had resulted from prolonged neck extension during surgery,” they wrote.

However, MRI and CT quickly ruled out spinal cord injury or other traumatic lesions, the authors said.

Next, the patient underwent a neurological exam, which showed mild bilateral ptosis and some weakness in eye closure. The patient was given a bedside ice pack test on his eyelids, which suggested MG. Clinical and laboratory tests confirmed the diagnosis.

The investigators said it appears the drugs used during surgery aggravated the patient’s already impaired neuromuscular transmission, in effect “unmasking” the previously undiagnosed MG.

“Specifically, the NMJ in MG is exquisitely sensitive to nondepolarizing neuromuscular-blocking agents (eg, rocuronium), different classes of antibiotics (eg, aminoglycosides, ampicillin), possibly local anesthetics (eg, lidocaine), and glucocorticoids,” they wrote.

The administration of such drugs during surgery likely had a negative impact on the availability of acetylcholine and on acetylcholine receptor function, they added.

“In addition, more recently published work has demonstrated that reversal of NMB with neostigmine and glycopyrrolate tends to be incomplete, with a reported incidence of residual NMB of up to 63.5% at tracheal extubation and 56.5% at arrival in the postanesthesia care unit,” they wrote. “Any degree of residual NMB would have contributed to this patient's clinical picture.”

The authors noted that the ice pack test works by increasing the availability of acetylcholine in the NMJ, which is also why it works well as a test for MG.

Although this case revolved around a patient with undiagnosed MG, the authors noted that the case also illustrates the complexity of surgery-related pharmacology in patients with known MG. They said such cases require careful preoperative planning to preserve the function of the compromised NMJ.

Reference

Meiler SE, Siwemuke TJ, Postma GN. New-onset myasthenia gravis mimics spinal cord injury after Zenker's diverticulum repair. OTO Open. Published online June 8, 2023. doi:10.1002/oto2.56