QMGS score as a predictor of myasthenic crisis after thymectomy in patients with severe myasthenia

Myasthenia gravis (MG) is caused by autoimmune lesion of neuromuscular junction with muscle weakness. This disease requires long-term pathogenetic and symptomatic therapy using medication and non-medication options. Thymectomy (TE) is a key treatment option. The most dangerous complication in patients with MG after TE is postoperative myasthenic crisis (POMC). The Quantitative Myasthenia Gravis Score (QMGS) is optimal for assessing the risk of POMC. There are no literature data on this score for dynamic assessment of patients with MG in preoperative period. Objective. To evaluate dynamics of QMGS scores in patients with severe myasthenia and initially high risk of POMC, to determine the criterion for optimal thoracoscopic thymectomy. Material and methods. A retrospective study included 18 patients with seropositive MG and QMGS score ≥16 who underwent TE under general anesthesia. We assessed QMGS score changes prior to TE under preoperative preparation and their relationship with POMC, spirometry parameters and treatment option. ROC analysis of QMGS score was performed to assess the risk of POMC. Results. QMGS score decrease was more significant in patients without POMC (11 (9;16) vs. 0 (0.0), U=0.5, p<0.01). After treatment, QMGS score before surgery had significant negative correlation with spirometry: vital capacity (r=–0.75, p<0.05) and forced vital capacity (r=–0.68, p<0.05). Preoperative QMGS score 16 was the best threshold for prognosis of POMC (AUC 0.94). Conclusion. In preoperative management of patients with severe MG and initially high risk of POMC, QMGS score < 16 should be achieved to prevent myasthenic crisis.