Ocular Myasthenia and Thymectomy

Abstract & Commentary

Source: Roberts PF, et al. J Thorac Cardiovasc Surg. 2001; 122:562-568.

Is thymectomy beneficial for ocular myasthenia gravis (OMG)? Between 1970 and 1998, 61 OMG patients, aged 14-73 years, underwent thymectomy at the University of California (Davis) Medical Center (n = 7) or the University of Rome (n = 54), and were followed up for a mean of 9 years. Diagnosis was made on the basis of a combination of symptoms, acetylcholine receptor antibody titer, repetitive nerve stimulation studies, or single fiber electromyography. Thymoma was present in 12. Transsternal thymectomy was performed in 55, transcervical in 6. Response to thymectomy was characterized as cured, improved, unchanged, or worse, depending on whether the patient was, respectively, symptom free and off medication, symptomatically improved and on less medication, symptomatically unchanged and on the same medication, or, lastly, symptomatically worse, on more medication, or dead. Overall, 71% were cured (n = 31, 51%) or improved (n = 12, 20%) by thymectomy, with 16 patients (26%) unchanged, 1 worsening, and 1 dying in the postoperative period. Improvement or cure was seen in 67% of the thymoma subgroup. Thymectomy, Roberts and colleagues conclude, is safe and effective in OMG.

Commentary

Thymectomy is an accepted indication for thymoma. Given surgical expertise and ICU care in the 21st century, it is safe. What remains unproven is whether, absent thymoma or thymectomy is more efficacious than optimal medical management in myasthenia, ocular or generalized.

Based on an exhaustive literature review, the Quality Standards Subcommittee of the American Academy of Neurology concluded that thymectomy is a therapeutic option for nonthymomatous myasthenia gravis, but that its benefit has not yet been conclusively established (Gronseth GS, Barohn RJ. Neurology. 2000:55:7-15, Rubin M. Neurology Alert. 2000;19:1-2). The evidence for thymectomy in OMG is even weaker. Assuming it has a therapeutic benefit for OMG, deciding whether it should be performed comes down to the following. If the morbidity and mortality of thymectomy are greater than those of OMG becoming generalized, with its attendant consequences, thymectomy is contraindicated. Can this question be accurately answered?

From 20-50% of OMG cases go into remission without thymectomy. No controlled studies compare this to a surgical group. If OMG remains so for a year, it will become generalized in only 15%. Symptoms are in most instances easily treated with a combination of pyridostigmine and prednisone, the latter often inducing remission. The argument for thymectomy in OMG remains unconvincing and will remain so unless a prospective trial comparing thymectomy to best medical management is undertaken. —Michael Rubin

Dr. Rubin, Associate Professor, Clinical Neurology, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.