Predictive factors of myasthenic crisis after extended thymectomy for patients with myasthenia gravis

Postoperative myasthenic crisis (POMC) is one of the serious complications after extended thymectomy for patients with myasthenia gravis (MG). This study aims to clarify the risk factors of POMC occurrence.

The clinical data of 55 MG patients (25 male, 30 female; median age, 51 years) who underwent extended thymectomy at Kyoto University from 2000 to 2013 were retrospectively reviewed. Surgical outcomes and pre- and perioperative predictive factors of POMC were analysed.

The preoperative Myasthenia Gravis Foundation of America stage was I, II, III and IV in 24, 22, 8 and 1 patients, respectively. Ten patients (18.2%) developed POMC; 6 required prolonged intubation over 24 h and 4 required reventilatory support. All patients were weaned after 5.6 (2-26) days of ventilator support, and were discharged. Univariate analysis revealed a correlation with a high preoperative anti-acetylcholine receptor antibody titre (P = 0.009), history of myasthenic crisis (MC) (P = 0.0004) and unstable MG after preoperative medical therapy (P = 0.003). Multivariate logistic regression analysis showed history of MC (odds ratio, 11.84; 95% confidential interval, 1.05-372; P = 0.045) and unstable MG (odds ratio, 29.45; 95% confidential interval, 2.00-1063; P = 0.013) independently predicted POMC. The surgical response rate was not significantly different between the two groups (66.7% with POMC, 85.4% without POMC; P = 0.334).

POMC occurred more frequently in unstable MG before surgery or in patients with a history of MC. Adequate preoperative medical therapy and perioperative care should be provided to these patients.