Robotic–Assisted Thymectomy in Patients with Nonthymomatous Myasthenia Gravis

doi:10.4236/ss.2011.27086

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Surgical Science, 2011, 2, 393-396

doi:10.4236/ss.2011.27086 Published Online September 2011 (http://www.SciRP.org/journal/ss)

Robotic–Assisted Thymectomy in Patients with

Nonthymomatous Myasthenia Gravis

Iskander Al-Githmi

Department of Surgery, Division of Cardiothoracic Surgery, King Abdulaziz University Ho spital, Jeddah,

Saudi Arabia

E-mail: [email protected]

Received August 2, 2011; revised August 23, 2011; accepted September 1, 2011

Abstract

Complete removal of the thymus and fatty tissue adherent to pericardium is crucial for treating myasthenia

gravis. Our aim was to analyze our surgical and clinical results and early experience of robot-assisted thy-

mectomy in patients with nonthymomatous myasthenia gravis. Between January 2008 and October 2010, 8

patients, all women, with nonthymomatous myasthenia gravis underwent robot-assisted thymectomy using a

3-port, left-sided approach. There were no operative mortality; 1 patient had left phrenic nerve injury. Com-

plete remission was achieved in 25% of the patients at 18 months’ follow-up. There was no significant

agreement between preoperative computed tomography and histopathology finding (kappa = 0.059; P = 0.85)

and no significant correlation between age and duration of symptoms (P = 0.51). Robotic-assisted thymec-

tomy is promising procedure. It can be performed safely and effectively. With follow-up greater than 12

months, 87.5% of the patients who underwent robot-assisted thymectomy demonstrated clinical improve-

ment.

Keywords: Myasthenia Gravis, Nonthymoma, Robot, Thymectomy

1. Introduction

Myasthenia gravis is an autoimmune disease affecting

postsynaptic nicotinic acetylcholine receptors at the neu-

romuscular junction block producing neuromuscular

transmission-producing muscular weakness of striated

muscles.

Thymectomy is an established therapy in treating my-

asthenia gravis. Ferdinand Sauerbruch performed the

first successful thymectomy in a patient with myasthenia

gravis in 1911 in Zurich [1]. The efficacy of thymectomy

depends on complete removal of all thymic tissue. In

1941, Blalock said, “Complete removal of all thymus

tissue offers the best chance of altering the course of the

disease” [2].

Multiple described surgical approaches to thymectomy

include transcervical thymectomy [3], transsternal thy-

mectomy [4], infrasternal subxiphoid mediastinoscopic

thymectomy [5], and video-assisted thoracoscopic thy-

mectomy [6-8]. Introduction of robotic surgical-assisted

system contributed to the field of minimally invasive

surgery [9]. Yoshino described the first robotic thymec-

tomy in treating small thymoma [10]. However; ro-

bot-assisted thymectomy has been reported with good

short-term results. Only scant data are available on the

long-term results of robot-assisted thymectomy for my-

asthenia gravis. It is uncertain which patients may benefit

from robot-assisted thymectomy. This study sought to

analyze the surgical and clinical results of robot-assisted

thymectomy in patients with nonthymomatous myasthe-

nia gravis.

2. Materials and Methods

Between January 2008 and October 2010, 8 patients all

women (mean age, 28 y; range, 16 - 46 y) with nonthy-

momatous myasthenia gravis referred by neurologists

underwent robot-assisted thymectomy by 1 cardiotho-

racic surgeon at King Abdulaziz University Hospital,

Jeddah, Saudi Arabia. Preoperative patient clinical char-

acteristics, duration of symptoms, preoperative acetyl-

choline receptors antibody, preoperative Osserman clas-

sification, and computed tomogram of chest finding are

shown in (Table 1).

The diagnosis of myasthenia gravis was based on

clinical features, result of electromyography (decrement-

394 I. Al-GITHMI

Table 1. Preoperative demographic data.

Patient Characteristics Number

Mean age (y) 28 (16 - 46)

Mean symptoms duration (m) 7.75 (3-12)

CT scan chest

 Hyperplasia

 Normal

3 (37.5%)

5 (62.5%)

Acetylcholine receptor antibody

 Positive

 Negative

5 (62.5%)

3 (37.5%)

Osserman stage

 Stage I

 Stage IIa

 Stage IIb

 Stage III

 Stage IV

0 (0.0%)

2 (25%)

5 (62.5%)

0 (0.0%)

1 (12.5%)

Medications

 Anticholinestrase

 Steroid

 Azathioprine

8 (100%)

5 (62.5%)

3 (37.5%)

tal response to repetitive nerve stimulation), and/or

demonstration of circulating antibodies against acetyl-

choline receptors.

Osserman classification was used for myasthenia gra-

vis staging: stage I, ocular myasthenia gravis; stage IIa,

mild generalized myasthenia gravis; stage IIb, moderate

myasthenia gravis with bulbar involvement; stage III,

acute fulminant myasthenia gravis; and stage IV, severe

late myasthenia gravis (Table 2).

Preoperative evaluation included thoracic computed

tomographic scan and pulmonary function test in all pa-

tients. Preoperative preparation included 3 sessions of

plasmapheresis in all patients. Informed consent was

obtained from all patients after explaining the procedure,

different approach of surgical technique, and potential

complications. The surgeries were performed using the

de Vinci system (Intuitive Surgical, Sunnyvale, CA,

USA) through a 3-port left-sided approach. The De

Table 2. Modified osserman classifications.

Stage Definition

I Ocular myasthenia gravis: involvement of extraocular

muscles with diplopia and ptosis.

IIa

Mild generalized myasthenia gravis: ocular symptoms are

associate to slow involvement of bulbar (dysphagia and

dysarthria) and skeletal muscles (generalized weakness).

Respiratory muscles are spared.

IIb

Moderately generalized myasthenia gravis: progressive

onset of symptoms with significant manifestation of

weakness. Respiratory muscles are spared.

III

Acute myasthenia gravis: rapid onset (within 6 months) of

severe bulbar and skeletal muscles involvement with

important weakness. Respiratory muscles are involved.

IV Severe late myasthenia gravis: progressive in severity for

2 or more years.

Filippi classification was used for postoperative outcome

clinical assessment (Table 3).

3. Surgical Technique

After general anesthesia induction avoiding the use of

nondepolarizing neuromuscular blocking agents, a dou-

ble-lumen endobronchial tube was placed for single lung

ventilation. The patient was placed in a supine position

with the left arm positioned as far back as possible to

gain enough space for robotic arms. Three skin incisions

were made along the left submammary fold; the camera

port (30-degree angled lens) was introduced through fifth

intercostal space along anterior axillary line. The right

and left robotic arms were introduced through fifth in-

tercostal space, midclavicular, and through third inter-

costal space, anterior to midaxillary line. The point of

reference to anterior mediastinum was the left phrenic

nerve. The left arm had an EndoWrist precise grasper;

the right arm has EndoWrist harmonic shear dissector.

After the robotic system was engaged, dissection started

inferiorly at the left pericardio-phrenic angle, and ex-

tended superiorly along the left phrenic nerve to the

jugular fold and continued inferiorly along retrosternal

area; the right pleural space was opened. The inferior

horn of thymus gland was isolated from the pericardium

and mobilized upwards. The dissection continued on the

right side with visualization of the right mediastinal

pleura and the right inferior horn. Isolation continued to

the neck until the superior horns were identified and iso-

lated. The innominate vein was identified, and dissection

continued along the border of the innominate vein to the

point where the thymic veins were identified, clipped,

and divided. The thymus gland and mediastinal fatty

tissue were removed en bloc, placed in endo-bag, and

retrieved through a trocar incision.

4. Results

The duration of symptoms ranged from 3 to 12 months

(mean, 7.75 months). The preoperative Osserman classi-

fication was stage IIa in 2 patients; stage IIb in 5 patients;

and stage IV in 1 patient. Anti-acetylcholine receptor

antibody was positive in 5 patients (62.5%) and negative

Table 3. De Filippi postoperative classification.

Class Description

1 Complete remission, no medication.

2 Asymptomatic, decreased medication.

3 Improved, decreased symptoms or decreased

medication.

4 No change.

5 Worsening symptoms.

I. Al-GITHMI

395

Table 4. Selected preoperative variables and patient outcome.

Follow-up/De Filippi Classification

Osserman

classification

Symptoms

duration (month) Preop CT chest Histopathology 6 months 12 months 18 months

1 16 IIb 12 Hyperplasia Thymic involution Class 4 Class 3 Class 2

2 19 IIb 3 Normal Normal Class 4 Class 2 Class 3

3 23 IIa 12 Normal Normal Class 4 Class 3 Class 3

4 26 IIb 12 Hyperplasia Normal Class 4 Class 4 Class 3

5 28 IIb 5 Hyperplasia Hyperplasia Class 3 Class 3 Class 2

6 30 IV 3 Normal Hyperplasia Class 3 Class 2 Class 1

7 36 IIb 7 Normal Hyperplasia Class 3 Class 3 Class 2

8 46 IIb 8 Normal Thymic involution Class 3 Class 2 Class 1

in 3 patients (37.5%). The preoperative thoracic com-

puted tomogram showed normal anterior mediastinum in

5 patients (62.5%) and an enlarged thymic gland in 3

patients (37.5%). The operative time ranged from 88 to

300 minutes (mean, 260 min). All patients were extu-

bated in the operating suite. There was no operative

mortality. One patient developed postoperative myasthe-

nia crisis on day 3 and required endotracheal intubation

and mechanical ventilation and was successfully man-

aged with plasmapheresis and weaned of mechanical

ventilation on postoperative day 9. One patient had left

phrenic nerve injury. Histopathologic examination of the

specimens revealed normal thymus in 3 patients (37.5%),

thymic hyperplasia in 3 patients (37.5%), and thymic

involution in 2 patients (25%). Additionally, histopa-

thologic findings correlated with preoperative computed

tomogram of chest, revealing hyperplasia in 2 patients

(25%), which was reported normal on preoperative

computed tomogram that was not clinically significant

(kappa = 0.059; P = 0.85)

Six months’ follow-up showed improvement, decr-

eased symptoms (class 3) in 4 patients (50%), and no

change in symptoms or decreased medication in 4 pa-

tients (50%). Twelve months’ follow-up showed a

symptomatic, decreased medication (class 2) in 3 pa-

tients (37.5%) and improvement, decreased medication

(class 3) in 4 patients (50%). One patient (12.5%) ex-

perienced no change in symptoms or decreased medica-

tion (class 4). At 18 months, complete remission was

shown in 2 patients (25%), a symptomatic, decreased

medication (class 2) in 3 patients (37.5%), and im-

provement, decreased medication (class 3) in 3 patients

(37.5%) (Table 4).

5. Discussion

Thymectomy is an established therapy in treating myas-

thenia gravis combined with medical treatment [11].

Robot-assisted thymectomy is promising technique;

however, complete removal of the thymus gland is cru-

cial. Compared with video-assisted thoracoscopic thy-

mectomy, the robot-assisted technique provides several

advantages, particularly, in the corner of anterior medi-

astinum, which is difficult to reach with video-assisted

thoracoscopy. In addition, 3-dimensional visualization,

high-dexterity, and full range motion of EndoWrists,

make the robot system safe and efficient. We adopt the

left-sided approach and the use of pneumomediastinum

to facilitate dissection of thymus gland and perithymic

fatty tissue as proposed by Mineo and colleagues [6]. We

believe that left-sided approach offers excellent visuali-

zation of the left pericardiophrenic angle and aortopul-

monary window.

Our postoperative clinical results are good. Clinical

improvement is demonstrated in 87.5% of patients who

underwent robot thymectomy at follow-up greater than

12 months. These results are comparable to those re-

ported by others through a transsternal approach [4]. In

addition, clinical improvement continued over time, as

we have noted that complete remission is achieved in

25% of patients at 18 months’ follow-up. Regarding

preoperative computed tomogram of chest and histologic

findings, we observed no clinical significant correlation

in patients with nonthymomatous myasthenia gravis re-

ferred for thymectomy. This suggests that preoperative

computed tomogram has a limited role in differentiating

the nonthymomatous pathology in patients with myas-

thenia gravis. In addition, we observed no significant

correlation between symptom duration and age. We were

inclined to follow our patients using guidelines set by

Jaretski and colleagues [12].

Our study is limited, as the number of patients is small

and difficult to perform a multivariate analysis of inde-

pendent factors that affect the outcome. Long-term fol-

low-up is necessary for proper assessment of clinical

results.

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