Prognostic factors of thymectomy in patients with myasthenia gravis: A cohort of 132 patients

Objective: To identify the response to thymectomy and the factors associate d with a poor response, a nested case-control study was performed on 132 pa tients with an established diagnosis of myasthenia gravis who had had a thy mectomy between 1987 and 1997 and had been followed up for at least 3 years . Methods: In order to assess the response to thymectomy, the following two points were taken into account: (a) the dose of pyridostigmine and other d rugs (steroids, azathioprine) that the patient took before and after thymec tomy, and (b) the Osserman classification before and after thymectomy. The patients were divided into 4 groups: (1) patients in remission; (2) patient s with improvement; (3) patients with no change, and (4) patients who were worse. Results: 91 patients had a good response (69%) and 41 patients had a poor response (31%). The response by groups was as follows: 50 patients we re found to be in remission; 41 patients had improved; 34 patients had no c hanges, and 7 got worse. Being more than 60 years old was associated with a poor prognosis (odds ratio 4.6, Cl 1.11-20.32, p 0.01). The patients who h ad the disease for more than 3 years (odds ratio 2.97, Cl 0.79-5.39, p 0.09 ) had a tendency towards a bad prognosis even though there was no statistic al significance, and for those who had it for more than 4 years (odds ratio 2.58, Cl 0.89-0.96, p 0.02) the bad prognosis was statistically significan t. The patients who had the disease for more than 3 years between diagnosis and thymectomy (odds ratio 2.02, CI 0.69-5.90, p 0.15) and those with it f or more than 4 years (odds ratio 2.53, Cl 0.83-7.7, p 0.06) had a tendency towards a poor prognosis even though there was no statistical significance. In addition, having Osserman I was associated with a bad prognosis. Referr ing to the pathological findings, patients with thymoma (odds ratio 3.51, C l 0.43-31.5, p 0.15) and those with thymic atrophy (odds ratio 2.19, Cl 0.9 3-5.16, p 0.04) had a poor prognosis. Finally, the use of steroids before t hymectomy (odds ratio 2.26, Cl 0.99-5.18, p 0.03) was associated with a wor se prognosis. Conclusions: The response to thymectomy was high (69%). The v ariables that had the most prognostic importance were age and the Osserman stage. Other variables of poor prognosis were: high doses of pyridostigmine and use of steroids before surgery; the total duration of the disease and the duration of the disease between diagnosis and the surgical procedure; h istory of previous thymectomy; use of plasmapheresis after surgery, and the discovery of thymic atrophy and thymoma in the histopathological result. C opy right (C) 2001 S. Karger AG, Basel.