Preliminary results of VATS thymectomy for pediatric myasthenia gravis
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- Parikh, K., Vaidya, A. & Jain, R. Pediatr Surg Int (2011) 27: 595. doi:10.1007/s00383-010-2838-4
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Myasthenia gravis (MG) is a debilitating disease which necessitates long-term medical therapy. If left untreated, it can have a high mortality rate. The commonest variety in children, the autoimmune variety, often requires recourse to immunomodulation including prolonged usage of high-dose steroids. Thymectomy has not been a popular option among treating clinicians. There is evidence to suggest that if thymectomy is performed early in the disease, it has a high success rate in reducing the doses of the oral steroid medication and also in inducing remission of the disease. We have performed video-assisted thoracoscopic surgery (VATS) thymectomy in four patients with the autoimmune variety of MG. In this study, we have had a fair and comparable success rate as with the other adult series. On the basis of this preliminary study, we recommend that the option of VATS thymectomy should be offered to select patients of MG.
KeywordsMyasthenia gravisVATS thymectomy
Myasthenia gravis (MG) is a debilitating disease which necessitates long-term medical therapy. The commonest variety in children—the autoimmune variety  often requires prolonged usage of high-dose steroids in addition to the other medications. Although the role for thymectomy is undisputed in case of detection of a thymoma, there has been a lack of consensus on the role of thymectomy in the patients without a thymoma [2–4]. We have performed video-assisted thoracoscopic surgery (VATS) thymectomy in four patients with the autoimmune variety of MG. The long- and short-term results are being studied to consider whether this modality can be recommended for all appropriately selected cases of MG.
Materials, methods and results
FU period (months)
Each of these patients was subjected to a complete thymectomy with a right mediastinal clearance using a VATS approach with three or four ports. The estimated blood loss ranged between 10 and 25 ml. The operative time ranged from 2.5 h to 55 min. We had placed an intercostal drain in each of these patients, but it was removed within 24 h. The patients were observed in the intensive care unit for <24 h, and were then kept in the hospital for two more days. On the day of discharge, they were completely pain free and did not require any medication for the same. There were no intra-op or post-op complications.
The patients were discharged on their pre-op medication schedule and the same was not changed for the first 3 months after which the steroids were gradually tapered. In patients 1 and 2, the steroids were progressively tapered and both of them are free of steroids now. The patient 3 is on a very small dose of steroid at present which is being tapered gradually. Patient 4 has got just minimal response till now and continues to be on pyridostigmine and a smaller dose of steroid.
- The patient was placed in a left semi-lateral position on the table close to the edge of the table (Fig. 1).
- The port positions were as shown in the Fig. 2.
The chest was entered by an open technique and the lung was collapsed to visualize the mediastinum.
The mediastinal pleura was opened anterior to the right phrenic N. mediastinal fat if any was removed.
The thymus gland was identified anterior to the brachiocephalic V which was traced along the superior vena cava.
The inferior thymic vessels were traced at the lower pole, coagulated and divided.
The lobe was then traced superiorly till the upper pole and the upper polar vessels were similarly divided.
The right lobe of the gland was then lifted to identify the median thymic v which is a direct short, but stout tributary of the brachiocephalic V. this vessel needs to be carefully clipped and divided.
The dissection is similarly proceeded to the left lobe of the gland. The confirmation of the completeness of the removal of the thymus is made by visualizing the mediastinal pleura on the left side.
- The entire gland is then retrieved from one of the ports (Fig. 3).
All the mediastinal fat from the right mediastinum is removed.
An intercostal drain was inserted in each of the cases.
Myasthenia gravis is a relatively rare chronic disease characterized by rapid fatigability of striated muscle. The most frequent cause is an immune-mediated neuromuscular blockade .The general incidence of the disease is supposed to be around 2/100,000 , but various studies have placed the incidence in US from 0.5 to 14.2 cases per 100,000 people . The female:male ratio in children is 3:1 when compared with almost 1:1 in the adult-onset MG . In children, there is a congenital variety and also a hereditary variety of the condition, but the most frequent cause is an immune-mediated neuromuscular blockade and the disease is generally non-hereditary . Although any patient who develops symptoms before the age of 20 years  is labeled to have a juvenile variety, patients may develop symptoms as early as late infancy or early childhood.
Electromyography (EMG) is an important diagnostic investigation in MG . All our four patients had a positive EMG diagnosis. Anti-ACh antibodies should be assayed in the plasma, but are inconsistently demonstrated. About 1/3 of affected adolescents show elevations, but anti-ACh receptor antibodies are only occasionally demonstrated in the plasma of prepubertal children ; 3 out of our 4 patients, who were subjected to thymectomy, were positive for anti-Ach antibodies.
If untreated, MG is usually progressive and may become life threatening because of respiratory muscle involvement and the risk of aspiration, particularly at times when the child is otherwise unwell with an upper respiratory tract infection .The primary treatment of MG has been medical with pyridostigmine . The role of the thymus in the pathogenesis of MG is not entirely clear, but 75% of patients with MG have some degree of thymus abnormality (e.g., hyperplasia in 85% of cases, thymoma in 15% of cases) . Given the immunologic function of the thymus and the improvement in the clinical condition of patients following thymectomy, the thymus is suspected to be the site of autoantibody formation. Although the preoperative presence of anti-Ach antibodies indicates a possibility of a significant response to thymectomy [7, 8], there have been reports wherein the patients have responded to thymectomy despite being negative for the anti-Ach antibodies .
There has been some reluctance in offering thymectomy as a treatment modality to children considering the potential of compromising the long-term immunity in them. However, in various studies, where thymectomy has been done in children, there has not been any adverse effect reported [6, 9]. In our series, all the patients who were subjected to thymectomy had required oral steroids as immunotherapy; besides, the pyridostigmine. Thymectomy was able to completely spare two of the younger patients from regular steroid intake and the third patient is being weaned off the steroids at present.
There is some evidence which suggests that thymectomy is most useful if done earlier in the course of the disease (between 1 and 2 years of onset) [1, 2]. In our series, three patients were operated within 1 year after being diagnosed; however, the fourth patient opted late for the surgery and his response so far has been less satisfactory. There have, however, been reports of late response (as late as a few years) to thymectomy too [2, 9].
Thymectomy as a therapeutic modality for MG has been practiced since 1911 . Till recent years, the approach to the thymus was either trans-cervical or trans-sternal . Although the former was technically more challenging, it was a relatively blind procedure and there was distinct possibility of leaving behind some ectopic thymic tissue. The trans-sternal route offered a possibility of more complete removal of thymic tissue and mediastinal clearance, but this was at the expense of a significant morbidity of the procedure and thus had much lesser patient compliance. There have thus been attempts at combining the trans-cervical surgery with a thoracoscopic visualization to ensure completeness .
The fact that the best response to thymectomy is seen if operated early in the course of the disease, a significant number of patients and treating neurologists are more likely to resort to this option early if effective surgical results can be offered with minimal morbidity. Over the past two decades, there have been multiple reports in adults, where the success of trans-sternal thymectomy has been compared with the results of thoracoscopic thymectomy [3, 12, 13]. These have now confirmed the effectiveness of VATS thymectomy [5, 7, 8, 12, 14, 15]. Although some of the reports have suggested the need to perform a bilateral VATS, this suggestion has not yet been consistent in all studies. There have also been some suggestions to approach the thymus from the left chest, but others have highlighted the problems of the arch of aorta and difficulty in accessing the brachiocephalic vein through this approach, and have preferred the right chest approach .
Most studies for VATS thymectomy have been done in adults and there are limited reports in the sub-adolescent population [5, 17, 18]. This is possibly the first series of four pediatric patients from the Indian subcontinent and our first patient who was only 2.5 years was possibly the youngest reported for the same. Our present study has restricted the procedure to a unilateral approach, but with complete removal of the mediastinal fat from the right mediastinum. In our short series, we could wean off the patients of the steroids approximately 3 months onwards. At present, we have had 75% response to the surgery which is comparable to most international studies [6, 19]. The follow-up period is still not very long to opine on the long-term effects.
Myasthenia gravis is characterized by weakness and rapid fatigability of voluntary muscles. It is a chronic disease that can have a high mortality rate if left untreated. Many children do not respond to the regular line of medication and they need recourse to immunomodulation. Thymectomy has not been a popular option among treating clinicians. This has possibly emerged due to the morbidity of a sternotomy and the technical difficulties combined with the possible inadequacies of a cervical thymectomy.
There is evidence to suggest that if thymectomy is performed early in the disease, it has a high success rate in reducing the doses of the oral steroid medication and also in inducing remission of the disease. Whereas the primary treatment options will remain with the pediatrician or the pediatric neurologist, thoracoscopic thymectomy would increase the acceptance of thymectomy as a treatment option for the primary treatment clinicians, as well as the patients and this may help in changing the long-term prognosis of this disease. This is a preliminary study in four pediatric cases with a fair and comparable success rate with the adult series. On the basis of this preliminary study, we recommend that the option of VATS thymectomy should be offered to select patients of MG.