Abstract
Acute respiratory distress after thyroidectomy may be seen in patients who develop postoperative hemorrhage or in patients who have injury to the recurrent laryngeal nerve during surgery. We report an unusual case of postoperative acute respiratory failure caused by myasthenic crisis.
A 28-year-old woman presented with a slowly enlarging neck mass without compressive symptoms. There was no pertinent history of irradiation to head and neck. For the previous 2 months, she had experienced an altered sense of taste but no muscle weakness or reduced exercise tolerance. On palpation, a hard, irregular, 5-cm tumor was noted in the right lobe of the thyroid. The remainder of the examination, including neurological evaluation, and her medical history were unremarkable. Her thyrotropin (thyroid-stimulating hormone, TSH) level was normal at 2.65 mU/L. Ultrasound revealed enlarged lymph nodes in her central and right lateral neck. Fine-needle aspiration cytology confirmed the presence of papillary thyroid carcinoma. The patient proceeded to total thyroidectomy plus central and right lateral node dissection.
At surgery, the tumor was found to have extensive extrathyroidal invasion of the strap muscles and tracheal cartilage. Gross extracapsular spread of metastatic regional lymph nodes (levels II–IV of the right side and ipsilateral level VI) was also evident. The right recurrent laryngeal nerve was completely encased by the bulky tumor; therefore, the nerve was sacrificed. The left lobe of the thyroid was essentially unremarkable and was removed with the right lobe. A shaving procedure was performed to resect the tracheal lesion without transmural perforation. Central and lateral neck dissection comprising en bloc removal of all fibrofatty and lymphatic tissue was then carried out in a compartment-oriented manner. Final pathological analysis showed locally advanced papillary thyroid cancer arising from the right lobe and two small hyperplasic nodules within the left lobe. There was no poorly differentiated component. The remaining thyroid tissue appeared normal and revealed no features of thyroiditis.
In the immediate postoperative period, the patient complained of hoarseness and secretion retention. Laryngoscopy revealed a complete right vocal fold palsy but preserved vocal cord mobility on the left side. On the next day, she developed problems with breathing and deglutition. There was no evidence of hematoma formation or subcutaneous emphysema. Initially, she was treated with supplemental oxygen, chest physiotherapy, inhalation therapy with bronchodilators and mucolytics, and parenteral corticosteroids. No significant improvement was observed. Two days after thyroidectomy, she was transferred to intensive care unit, intubated, and mechanically ventilated because of poor cough and airway clearance, shortness of breath, drooling, and swallowing difficulties. Chest X-ray showed partial collapse of both lungs.
On the day of intensive care unit admission, the patient began to complain of diplopia and limb weakness. Right upper eyelid ptosis was noted. An ice pack test was positive for myasthenia gravis (MG). Electromyography studies showed significant decrement on repetitive nerve stimulation, consistent with elevated serum acetylcholine receptor (AChR) antibodies at 39.28 nmol/L (normal value, <0.2 nmol/L). The patient was started on plasmapheresis along with steroids and cholinesterase inhibitors. Her dysgeusia resolved after plasma exchange, but respiratory function showed little improvement. A suppression dose of levothyroxine was given to avoid prolonged TSH stimulation. Noncontrast computed tomography of the chest revealed a 4-cm tumor in the left anterior mediastinum (Fig. 1) and two subcentimeter pulmonary nodules (one in the left upper lobe and the other in the right lower lobe) suggestive of metastases from thyroid cancer. The patient underwent thymectomy 3 weeks after thyroid surgery. Histological examination confirmed the diagnosis of type B2 thymoma.
Computed tomography of the chest showing a thymoma (arrow) in the left anterior mediastinum, which was neither evident on chest X-ray nor recognized during neck dissection.
After thymectomy, the patient had refractory respiratory failure and difficult weaning from mechanical ventilation despite additional eight sessions of plasma exchange. Her AChR antibody level was 50.24 nmol/L at 3 weeks postthymectomy. Ultimately, she underwent tracheostomy and was then successfully weaned from mechanical ventilatory support. The patient was discharged from the hospital with a hospitalization time of 4 months.
After discharge, pharmacological treatment (pyridostigmine, prednisone, and azathioprine), supportive measures, and respiratory rehabilitation were continued. Serum thyroglobulin was undetectable with a suppressed TSH below 0.1 mU/L. The tracheostomy tube was removed 4 months after tracheostomy (6 months after initial thyroidectomy). To prevent recurrence of myasthenic crisis, radioactive iodine treatment was administered with the use of recombinant human TSH (Thyrogen, Genzyme Therapeutics, Cambridge, MA; 0.9 mg intramuscular for 2 consecutive days) without thyroid hormone withdrawal. She was treated with 200 mCi (7.4 GBq) of 131I uneventfully. The pulmonary nodules were not seen on posttherapy whole-body scan or on follow-up spiral computed tomography imaging. She remains well without recurrence of papillary thyroid cancer or myasthenic crisis after 1 year of follow-up.
MG is associated with an increased frequency of thyroid disease (1). Epidemiological studies showed that autoimmune thyroid diseases occur in 5–10% of patients with MG, but MG is relatively uncommon in patients with autoimmune thyroid disease (2). It has been observed that MG associated with autoimmune thyroid diseases has a mild clinical presentation, preferential ocular involvement, and lower frequency of thymic disease and AChR antibodies (2). In addition, Graves' disease is slightly more common than Hashimoto's thyroiditis among patients with both MG and autoimmune thyroid diseases. In our patient, anti-TSH receptor and anti-thyroperoxidase autoantibodies were not measured at the time of diagnosis, whereas anti-thyroglobulin autoantibody was negative. Nonetheless, there was no evidence of autoimmune thyroid disease on histological examination.
Myasthenic crisis may be the initial manifestation of MG. Most cases of crisis are provoked by infection, surgery, emotional upset, and certain drugs (3). Of note is the fact that the onset may be preceded by several days of respiratory difficulty and not infrequently associated with an attack of the common cold (4). Sputum retention has been identified as a contributory factor. In our patient, a plausible explanation is that unilateral vocal cord palsy increases respiratory muscle work and perceived exertion, which in turn induces the attack of crisis. However, surgical stress per se may precipitate a crisis, and in some patients, no predisposing factor can be found.
When a crisis occurs, there should be a low threshold for endotracheal intubation and ventilatory support because weakness increases with repeated muscle use. Early recognition is of paramount importance. As depicted, the diagnosis may not be made until full-blown features of MG are demonstrated. The only clue in our patient to the early diagnosis is dysgeusia, which is an extremely rare presentation of MG (5). Understandably, AChR antibodies block acetylcholine receptors at postsynaptic neuromuscular junctions without effects on sensory synapses. It has been hypothesized that this phenomenon results from an unknown thymoma-produced antibody to taste receptors.
Nonautoimmune thyroid diseases do not seem to influence the features of MG (2). Our case may represent a coincidental event. However, thyroid surgery is usually performed on young female patients. Similarly, the incidence of MG is twice as high in women compared with men, with a peak incidence in the childbearing years (3). Our report highlights the possibility of this association, and MG crisis should be included in the differential diagnosis of postthyroidectomy respiratory failure. Awareness of this combination may help early identification, prompt intervention, and, if possible, prevention of the impending crisis.