Relationships between the pathology classification, Masaoka clinical stage and postoperation myasthenic crisis in patients of myasthenia gravis with thymoma

Objective To investigate the relationships between the pathology classification, Masaoka clinical stage and postoperation myasthenic crisis in patients of myasthenia gravis with thymoma undergoing thymectomy. Methods Clinical records of 56 patients of myasthenia gravis with thymoma from January 2006 to December 2015 who had underwent thymectomy were reviewed retrospectively. The following factors were analyzed to find the relation to the occurrence of myasthenic crisis after thymectomy: WHO pathology classification, Masaoka clinical stage and tumor size. Results Sixteen patients experienced postoperative myasthenic crisis after thymectomy. Statistical analysis revealed that the incidence of postoperative myasthenic crisis in patients with Masaoka Ⅲ stage was significantly higher than that in patients with Masaoka Ⅰ and Ⅱ stage: 39.39%(13/33) vs. 13.04%(3/23), the incidence of postoperative myasthenic crisis in patients with WHO pathology classification B3 and C type was significantly higher than patients with WHO pathology classification B2 type: 50.00%(12/24) vs. 14.29% (4/28), the incidence of postoperative myasthenic crisis in patients with tumor size more than 5 cm was significantly lower than patients with tumor size less than 5 cm: 10/17 vs. 15.38%(6/39), and there were statistical differences (P<0.05 or<0.01). Conclusions WHO pathology classification and Masaoka clinical stage are significantly correlated with the occurrence of myasthenia crisis after thymectomy. The patients with Masaoka Ⅲ stage, WHO pathology classification B3 and C type and tumor size more than 5 cm have the risk of postoperative myasthenic crisis after thymectomy. The comprehensive intervention before and after operation can prevent myasthenia crisis. Key words: Myasthenia gravis; Thymoma; Myasthenic crisis; WHO pathology classification