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Eur J Cardiothorac Surg 2003;24:677-683
© 2003 Elsevier Science NL
a Division of Thoracic Surgery, Toronto General Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada
b Division of Neurology, Toronto General Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada
c Department of Anesthesia, Toronto General Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada
Received 29 March 2003; received in revised form 28 July 2003; accepted 6 August 2003.
* Corresponding author. Division of Thoracic Surgery, EN 10-224, Toronto General Hospital, 200 Elizabeth Street, Toronto, M5G 2C4 Ontario, Canada. Tel.: +1-416-340-4010; fax: +1-416-340-4556
e-mail: Shaf.Keshavjee{at}uhn.on.ca
| Abstract |
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Key Words: Myasthenia gravis Thymectomy Video-assisted Thymoma
| 1. Introduction |
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Blalock's initial experience in the early 1940s and subsequently published series of surgically treated patients led to the widespread acceptance of thymectomy in the treatment of MG despite the absence of a prospective randomized trial comparing surgery with medical treatment alone [2]. Controversies remain, however, with regard to the timing and extent of surgery to be performed. Some authors recommend thymectomy early in the course of the disease, whereas others reserve surgery for when medical therapy fails or if a thymoma is suspected. Different surgical approaches have been recommended including trans-cervical, trans-sternal, and more recently a trans-thoracic thoracoscopic thymectomy [35]. All procedures allow extracapsular resection of the thymus and vary somewhat in the extent of mediastinal fat removal, which may contain foci of thymic tissue [6,7]. The most extensive resection combines the trans-cervical and trans-sternal thymectomy procedures and includes removal of all mediastinal fatty tissue, both sheets of mediastinal pleura along with a sharp dissection of the pericardium [8].
The trans-cervical approach was first described at the turn of the 20th century for thymic enlargement in children and consisted of an enucleation of the thymus from within its capsule [9]. Although initially reported in an adult patient with MG by Sauerbruch in 1912 [10], the trans-cervical approach was modified to completely remove the thymus with its capsule and reintroduced in the 1960s for patients with MG [11]. Through this approach, Kark and Kirschner reported fewer postoperative complications when compared to the trans-sternal approach [11]. Consequently, their patients were operated on earlier in the course of the disease and were shown to have more rapid rate of improvement [12].
In our institution, we have used a similar approach associated with the routine use of a videothoracoscope introduced through the cervicotomy to improve visualization of the mediastinum. This approach combined with early surgical referral, optimization of preoperative medical status when necessary by plasmapheresis, and careful perioperative management has led to greatly improved care of patients with MG. Herein, we report the short and long-term outcome in a series of 120 consecutive patients operated upon in our center.
| 2. Material and methods |
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2.2. Preoperative care and timing of operation
The diagnosis of MG was confirmed by physical examination, a positive response to anticholinesterase test, and single fiber electromyography (EMG). Detection of AchR antibodies by radioimmunoassay was not performed routinely. After the diagnosis was confirmed, MG symptoms were medically stabilized and patients were referred to the surgeon for thymectomy. In our institution, all patients with MG are referred to one surgeon (SK) for evaluation of thymectomy, and all patients undergo video-assisted trans-cervical thymectomy unless there is a contraindication, e.g. the presence of a thymoma on the computed tomography (CT) scan. Patients were usually referred to surgery unless they were over 50 years of age or with ocular symptoms only, in which case the decision to proceed with surgery was made on a case by case basis. Pyridostigmine was used as the first line of therapy. Prednisone and other immunosuppressive agents were started in the presence of persistent symptoms. A course of five plasmapheresis treatment was administered before surgery in patients with severe generalized weakness and/or with bulbar symptoms. Since 1998, a few patients with severe bulbar symptoms have been treated with high dose intravenous immunoglobulin (IVIg) instead of plasmapheresis prior to surgery. Over the years, we have progressively limited the administration of immunosuppressive therapy before surgery and preoperative stabilization is most often accomplished with pyridostigmine and plasmapheresis only.
All patients had a CT scan of the thorax before surgery in order to exclude a thymoma. If a thymoma was detected a trans-sternal approach was always chosen. Relative contraindications to a trans-cervical approach included prior cervico-mediastinal surgery and/or radiation, and cervical spine pathology limiting extension of the neck. Age, gender, obesity, and exposure to steroids were not considered contraindications to the trans-cervical approach.
2.3. Perioperative management
Anesthetic assessment was performed at an ambulatory preadmission clinic visit. Patients were admitted on the day of surgery. They either took their morning dose of pyridostigmine as usually scheduled or took it immediately prior to surgery. If surgery was delayed or scheduled for the afternoon, another dose of pyridostigmine was given before surgery. No other premedication was administered. Anesthesia was induced with propofol and fentanyl, and was maintained with isoflurane and nitrous oxide. Propofol was often used in addition to inhaled anesthetics for maintenance of anesthesia. Muscle relaxation was rarely required. Patients were routinely extubated at the end of surgery. Analgesia was given orally using acetaminophen with or without codeine. Morphine was rarely required. Oral pyridostigmine at the patient's usual dose was reintroduced 46 h after surgery. If patients were on steroid therapy before surgery, an intravenous dose was given preoperatively and oral steroids were continued the next morning. Patients were ready to be discharged the next day if their symptoms were stable and pain was controlled. Postoperative complications included all complications occurring within 30 days of surgery.
2.4. Surgical procedure
Surgery is performed in the supine position. The neck and full anterior chest were prepped in case a sternotomy is required. A curvilinear incision is made in the skin at the base of the neck, one finger breadth above the sternal notch, and extended on each side to the medial border of the sternocleidomastoid muscle. The superior poles of the thymus gland are dissected, and the thymus gland is followed inferiorly to the thoracic inlet. A retrosternal space is cleared to accommodate the placement of the Cooper retractor [13] and the upper hand retractor (Poly-Tract, Pilling Company, Fort Washington, PA) is then set up with the Cooper thymectomy retractor blade (Pilling Company), which is then placed beneath the manubrium to elevate it and open the thoracic inlet. Care is taken to make sure that the patient's head is not elevated off the operating table by the sternal retraction. A 30° videothoracoscope is then placed at the right lateral aspect of the neck incision to provide light for direct operating and a video magnified view of the operating field on a monitor for the surgeon and assistants. The thymic veins draining into the innominate vein are identified posteriorly and divided between stainless steel clips. The arterial vessels entering the gland laterally from the internal thoracic artery branches are also clipped with stainless steel clips. The dissection is carried down along the pleura to the inferior poles of the gland on both sides and along the pericardium. The assistance of the videothoracoscope provides good visualization of the lower mediastinum, down to the diaphragm if necessary. Once the gland is excised, if there is any further mediastinal fatty tissue present that is suspicious for being thymic tissue, this is excised or biopsied for frozen section analysis to ensure that no residual thymic tissue is left behind. If a complete thymectomy cannot be performed by removing the thymus and its capsule, the operation is usually converted to a partial upper sternotomy. This is carried out by the addition of a vertical skin incision extending down from the sternal notch to the lower end of the manubrium. The sternal incision is then extended laterally in the third or fourth intercostal space with the oscillating saw, to create a partial upper sternotomy, which provides sufficient exposure to easily complete the operation.
2.5. Follow-up
Fifty percent of the patients were followed by one neurologist with a special interest in the care of patients with MG (VB). These patients were reviewed at various intervals according to their status, but were seen at least every 12 months and as frequently as every 13 months. The remaining patients were followed by the attending surgeon (SK) on a yearly basis (30%) or were contacted by telephone (20%). Follow-up was complete if patients were reviewed or contacted between January 1 and December 31, 2000 with a minimum of 6 months follow-up since their surgery.
In order to compare our results with those of previous publications, we used definitions similar to those in other series. Complete remission is defined as asymptomatic without weakness and without any MG medications for at least 6 months; remission is defined as minimal ocular symptoms (slight ptosis) or treatment with pyridostigmine only for 6 months. The palliation rate included all patients on immunosuppression or with persistent mild to moderate symptoms despite MG treatment.
2.6. Statistical analysis
To document the evolution in our management and our results, we divided our study into three periods: the periods ranged from 1991 to 1994, 1995 to 1998, and 1999 to 2000. Data were analyzed by Fisher's exact test and Student's t-test where appropriate. Results are expressed as mean±SD, or as median and range. Life table analysis was tabulated by the KaplanMeier method with complete remission as the event of interest. Life table analysis with the log-rank test was used to assess the effect of the variables on the distribution of complete remission over time. Probability values <0.05 were considered to be statistically significant.
| 3. Results |
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On pathologic examination, the thymus was involuted in 60 cases, hyperplastic in 55 cases, and contained an incidental thymoma in five cases. All five thymomas were undetected on the preoperative CT scan and were discovered at the time of surgery only. Their size ranged from 1 to 3 cm (median 2 cm). Three of them required conversion to a sternotomy, whereas two small (1 cm), encapsulated thymomas located in the upper part of the thymus were safely removed through the trans-cervical approach. All five patients are alive without recurrence after 39111 months (median 97 months). The proportion of thymic involution was significantly higher among patients treated with steroids before surgery than among those not taking steroids (38 versus 16%, respectively; p=0.01).
One hundred patients were available for complete follow-up. Ten patients were lost to follow-up and 10 have been followed for less than 6 months and were not included in the outcome analysis. After a median follow-up of 48 months (range 6117 months), 41% of the patients were in complete remission and 9% were in remission. The improvement in Osserman grade was not different between patients whose thymectomy was completed via the trans-cervical approach and those who required conversion to an upper sternotomy (Table 3). Two patients presented with persistent myasthenic symptoms refractory to medical treatment and underwent re-exploration through a sternotomy 25 and 42 months after the trans-cervical approach despite the absence of residual thymic tissue on chest CT scan. One had thymic tissue in the anterior mediastinum discovered during the second surgery and subsequently became asymptomatic, whereas the other had no residual thymic tissue.
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40, 4160, and >60 years), latency of surgery (
8, 912, >12 months), and preoperative Osserman grade (stages IIV) also showed no significant differences (p=0.5, p=0.2, and p=0.9, respectively).
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Stratification according to the need for preoperative immunosuppressive therapy showed no significant difference at 10 years when compared to patients receiving only pyridostigmine before surgery (p=0.1). However, complete remission was achieved more rapidly in the group of patients treated without preoperative immunosuppression, reaching statistically significant differences after 5 years of follow-up (p=0.04) (Fig. 2).
| 4. Discussion |
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Video-assisted trans-cervical thymectomy combines video technology with the minimally invasive trans-cervical technique. This approach provides excellent visualization of the mediastinum along both pleura down to the diaphragm if necessary, and permits extended resection of the thymus gland and perithymic tissue both in the neck and in the mediastinum. There is no need for placement of a double lumen endotracheal tube, the pleural space need not be breached, and there is minimal requirement for more than oral analgesia in the postoperative period. The morbidity is extremely low with minimal complications (one hemothorax and one pneumothorax treated conservatively in our series). In addition, 63% of our patients were hospitalized for 24 h or less and 83% for 48 h or less. These results were significantly better than for the group of patients that required conversion to an upper sternotomy. Indeed, the majority of these patients were hospitalized for 34 days because they required patient-controlled analgesia with intravenous morphine sulfate, and two patients in this group experienced a myasthenic crisis during their postoperative course.
Although the rate of complete remission in the long-term is certainly the most important endpoint in determining the efficacy of any surgical approach for patients with MG, direct comparison between series has been difficult. Most authors report crude remission rates, which correspond to the overall number of remissions per number of thymectomies performed, after a mean length of follow-up [16]. The time from thymectomy to complete remission is, however, of prime importance as remission is a time-dependent event. In order to correct for variable length of follow-up and for patients lost to follow-up, Jaretzki has recommended the use of life table analysis to determine the rate of remission [16]. This mode of analysis has, however, been adopted by only a few authors [5,1719].
We agree that life table analysis, of which the KaplanMeier method is a refinement, is a more relevant statistical technique for the evaluation of remission when there is no competing risk, because it provides a complete description of the rate of remission over time. Crude data and life table analysis of complete remission comparing our experience with that reported in the recent literature are presented in Table 4. In our study, the crude rate of complete remission was 41% after a mean follow-up of 4.3 years, which is similar to most other studies reporting results after trans-cervical and/or trans-sternal thymectomy. The life table analysis, however, showed a complete remission rate of 30% at 5 years and 91% at 10 years of follow-up. These results demonstrate that most of our patients achieved complete remission between 5 and 10 years after thymectomy. A complete remission rate of 91% at 10 years compares favorably with other series reporting life table analyses [5,1719]. Durelli et al. [17] reported a complete remission rate of 30% at 5 years after trans-sternal thymectomy, and Jaretzki et al. [5] observed a complete remission rate of 81% at 8 years after extended (radical) cervico-mediastinal thymectomy.
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In conclusion, considerable improvement has been made since the time when only selected patients with severe MG unresponsive to medical therapy underwent thymectomy. Surgery was associated with prolonged postoperative mechanical ventilation leading to a high morbidity and mortality rates. Currently, trans-cervical thymectomy requires hospitalization for less than 24 h in the majority of cases and is associated with very little morbidity. Patients therefore tend to be referred earlier in the course of their disease when they are in a more stable clinical condition. In the long-term, this approach achieved complete remission in 91% of the patients.
| Acknowledgments |
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| References |
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