Risk factors of myasthenic crisis after thymectomy for thymoma patients with myasthenia gravis.

Objectives: Total thymectomy should be performed on thymoma patients with myasthenia gravis. The aim of the present study was to investigate the risk factors of postoperative myasthenic crisis (POMC) occurrence in these patients.

Methods: The clinical records of 127 thymoma patients with myasthenia gravis (68 men, 59 women; median age, 50 years) who underwent total thymectomy at our institution from 2005 to 2014 were retrospectively reviewed. The following factors were analysed in relation to POMC: gender, age, duration of symptoms, bulbar symptoms, smoking history, history of myasthenic crisis, comorbidities, perioperative pyridostigmine and prednisolone therapy, spirometric and blood gas parameters, Osserman stage, operation approach, major complications, World Health Organization (WHO) histologic classification, Masaoka stage and use of immunoglobulins or plasmapheresis.

Results: Thirteen patients (10%) experienced POMC and required intubation. All patients were weaned after 2-28 days (median 9 days) and were discharged. Univariate analysis revealed a correlation between POMC and Osserman-stage IIA-IV [odds ratio (OR) = 4.928, 95% confidence interval (CI) = 1.286-18.882, P = 0.01], bulbar symptoms (OR = 3.828, 95% CI = 1.112-13.176, P = 0.04), and forced expiratory volume in one second <70% pred forced expiratory volume in one second (OR = 4.856, 95% CI = 1.380-17.081, P = 0.02). In addition, more frequent POMC occurred in WHO type B2-B3 than in type A-B1 thymomas (OR = 8.118, 95% CI = 1.020-64.590, P = 0.03). Multivariate logistic regression analysis showed that WHO histologic classification B2-B3 (OR = 10.041, 95% CI = 1.228-82.090, P = 0.03) and Osserman-stage IIA-IV (OR = 5.953, 95% CI = 1.506-23.538, P = 0.01) independently predicted POMC.

Conclusions: Osserman stage (IIA-IV) and WHO type B2-B3 thymomas are independent predictors of POMC in thymoma patients with myasthenia gravis who have undergone total thymectomy. Thus, adequate perioperative care should be provided to these patients.