Anesthetic Management of a Patient with Advanced Anti-Myelin-Associated Glycoprotein Antibody Neuropathy in the Absence of Measurable Quantitative Neuromuscular Responses: A Case Report

Background and Clinical Significance: Anti–myelin-associated glycoprotein (MAG) antibody polyneuropathy is a rare, chronic IgM-mediated demyelinating peripheral neuropathy predominantly affecting sensory nerves in older adults, commonly in association with monoclonal gammopathy of undetermined significance. Reports describing anesthetic management in patients with this condition remain extremely limited, and no specific guidelines currently exist regarding neuromuscular blocking agent (NMBA) use or neuromuscular monitoring in this population. Case Presentation: A 79-year-old man with anti-MAG antibody polyneuropathy (diagnosed in 2007) and IgM monoclonal gammopathy of undetermined significance developed disproportionate progressive lower-extremity weakness and became wheelchair-dependent following COVID-19 infection in 2020. Preoperative evaluation revealed mildly reduced left ventricular function (ejection fraction 49%), mild chronic kidney disease, and marked intrinsic hand muscle atrophy with absent deep tendon reflexes. He was scheduled for robot-assisted radical cystectomy with ileal conduit diversion under combined general and thoracic epidural anesthesia. Before NMBA administration, neuromuscular monitoring was systematically attempted at the ulnar nerve (electromyography and acceleromyography, up to 60 mA/300 μs) and the corrugator supercilii; despite visible muscle contractions following peripheral nerve stimulation, neither modality produced reliable responses at either site. Given the inability to establish reliable monitoring, the administration of NMBAs was considered to carry an unacceptable risk of a prolonged, undetectable blockade. Anesthesia was maintained with deep sevoflurane (2.0–2.5% end-tidal) and remifentanil infusion without NMBAs, titrated to a bispectral index of 40–60. Tracheal intubation was accomplished via video laryngoscopy without NMBA. The 7 h and 30 min surgery was completed without patient movement or surgical compromise. Postoperatively, the patient developed transient upper airway obstruction attributed to glossoptosis, managed successfully with head elevation and nasopharyngeal airway insertion; supplemental oxygen was required until postoperative day 3, and the patient was discharged from the high-dependency unit on postoperative day 5. Conclusions: No measurable quantitative neuromuscular response could be obtained in this patient with advanced anti-MAG antibody neuropathy, despite appropriate application of electromyography- and acceleromyography-based monitoring and the presence of visible muscle contractions following peripheral nerve stimulation. In such circumstances, avoiding NMBA administration in favor of deep volatile or intravenous anesthesia with opioid supplementation may represent a reasonable, hypothesis-generating approach in carefully selected patients; this observation does not establish the general superiority of an NMBA-free strategy, and caution is warranted before generalizing it to procedures such as robotic surgery, in which profound neuromuscular blockade is often considered desirable.