Foreign Body Aspiration: A Presenting Sign of Juvenile Myasthenia Gravis

The patient was an 8-yr-old boy who experienced a choking episode while eating popcorn. Paramedics found that the child was cyanotic and had stridor and limited air movement, and they performed a Heimlich maneuver. The child coughed and regurgitated a large amount of popcorn. His ventilation improved, but he continued to have coarse breath sounds, stridor, and a weak voice. At the time of arrival in the emergency room, clinical examination indicated stridor, tachypnea, and poor air entry by auscultation. His oxygen saturation was 100% with 5 l O²delivered via  a nonrebreathing mask. His admitting vital signs were blood pressure of 120/90 mmHg, heart rate of 121 beats/min, and respiratory rate of 30 breaths/min. His estimated body weight was 25 kg. He was alert during the initial examination, but when not stimulated, he closed his eyes and was quiet on the emergency room stretcher.

Fifteen minutes after his arrival in the emergency department, a chest radiograph was obtained en route to the operating room. During transport to the operating room, his breathing was noted to be less stridorous with very limited gas exchange, and his oxygen saturation decreased despite increasing the oxygen flow to his nonrebreathing mask to10 l/min. He was transferred to the operating room table with an oxygen saturation of 70% and a heart rate of 60 beats/min. Positive-pressure ventilation with an anesthesia bag and mask provided effective ventilation, and his oxygen saturation increased to 100%. His pharynx was suctioned for a large amount of undigested popcorn. He was able to move his extremities and open his eyes without difficulty but continued to have very limited gas exchange with spontaneous ventilation. His ventilation was assisted, and an inhalation induction was initiated with halothane in 5 l O². Less than 2 min after halothane induction was started, he was unresponsive and apneic. His ventilation was controlled, and a 40-mg propofol bolus was administered before direct laryngoscopy and bronchoscopy. The bronchoscope was inserted, and a large amount of undigested popcorn and popcorn kernels were identified in the trachea. This was removed in the course of a 90-min endoscopy. Anesthesia was maintained with a propofol infusion of 100 μg · kg⁻¹· min⁻¹as well as 1.0–1.5% halothane administered via  the side arm of the Storz^®bronchoscope (Storz Endoscopy, Culver City, CA). No neuromuscular blocking agents were administered during endoscopy. His cardiorespiratory status was stable throughout the endoscopy with a mean blood pressure between 70 and 80 mmHg, a heart rate between 80 and 100 beats/min, and an oxygen saturation greater than 95%. This boy’s ineffective spontaneous ventilation en route to the operating room, his rapid loss of consciousness, and apnea during a halothane induction, as well as the large volume of aspirated material found during endoscopy, suggested an underlying neurologic condition.

After endoscopy, he was admitted to the pediatric intensive care unit and underwent ventilation via  an endotracheal tube. Approximately 2 h after his arrival in the pediatric intensive care unit, he was alert and responsive and maintained an oxygen saturation of 100% on a fraction of inspired oxygen (Fio²) of 0.21 with a respiratory rate of 25 breaths/min. He had an effective cough and sustained handgrip but was noted to have ptosis and difficulty maintaining a sustained head lift. The endotracheal tube was removed 3 h after his arrival to the pediatric intensive care unit. His parents arrived after his emergency bronchoscopy and provided a detailed history of his problems at school and at home during the preceding 6 months. At school, his performance had deteriorated because his speech was often unintelligible and his handwriting was illegible. In addition to his difficulties at school, he had stopped participating in an indoor soccer league because of his inability to keep up with his teammates. A head computed tomography scan was normal. He had been referred to speech and occupational therapists who were treating his hypernasal speech and gait disturbance. His parents reported that he seemed alert, active, and able to eat in the morning, but by the evening, he had difficulty holding his utensils, his speech was unintelligible, and he had trouble swallowing.

Clinical examination after his extubation confirmed global muscular weakness and ptosis. The differential diagnosis included myasthenia gravis, a motor neuron disorder, tick paralysis, botulism, a brain stem tumor, or syrinx. An electromyographic study of the right orbicularis oculi muscle showed a 50% decrement in response to repeated stimuli. After 3 min of facial muscle exercise, an 80% decrement in response to a 2-Hz stimulus was observed in this muscle group. Muscle studies in the distribution of the median nerve of the right forearm as well as the trapezius muscle did not show a decremental response with repeated stimuli at 2 Hz. JMG was diagnosed. Computed tomography of the chest and mediastinum indicated no thymic enlargement.

Administration of 60 mg oral pyridostigmine four times daily was started, and the patient was scheduled for plasmapheresis. After a subclavian double lumen catheter was placed during ketamine sedation, plasmapheresis was conducted on hospital days 4, 6, 8, 10, and 12. Each plasmapheresis replaced approximately 1.5 times the estimated plasma volume of the patient (1.7–1.9 l) with normal saline and 5% albumin. By the final plasmapheresis, he had minimal evidence of muscle weakness. He was discharged to his home with a pyridostigmine dosage of 60 mg orally, four times daily. He returned for elective cervical thymectomy 4 days later. Anesthesia was induced with propofol and maintained with sevoflurane and nitrous oxide for the 2-h operative procedure. After an uneventful operation and anesthesia, he underwent extubation in the operating room and was discharged from hospital the following morning. Six months after his thymectomy, he continues to be in remission and takes no medications.

This child’s presentation in myasthenic crisis was attributed to a more common problem in children—an aspirated foreign body. This report shows the importance of considering an undiagnosed neurologic or neuromuscular disease as an underlying cause of foreign body aspiration, particularly if the clinical presentation is in an older child. JMG is considered similar to the adult form but accounts for less than 2 or 3% of all patients with myasthenia gravis. 1–3Two other forms of myasthenia gravis occur in children. 4,5Transient neonatal myasthenia caused by placental transfer of acetylcholine receptor antibodies may be observed in as many as one fourth of neonates born to mothers with myasthenia gravis. Congenital myasthenic syndromes present in infancy or childhood and are believed to be a genetic defect of the neuromuscular junction rather than an autoimmune disorder of myasthenia gravis. 4,5 

Using the Osserman classification to define the severity of symptoms at diagnosis, children often present with more severe symptoms of myasthenia gravis. 6Fifty percent of prepubescent children present, like the current patient, with respiratory symptoms or myasthenic crisis (Osserman 3) at the time of diagnosis, compared to less than 10% of adults. 1–3Despite the more severe symptoms with JMG, no case reports have identified a myasthenia crisis as an underlying cause of foreign body aspiration in children.

This child’s deterioration en route to the operating room was initially believed to be the result of complete airway obstruction from movement of the foreign body, but his rapid response to bag and mask ventilation suggested that an underlying neurologic condition caused hypoventilation. 7,8Although positive pressure ventilation was used during the anesthesia, neuromuscular blocking drugs were not administered during this anesthesia. An undiagnosed neuromuscular disease as a predisposing cause of foreign body aspiration is another reason for caution in the use of neuromuscular blocking drugs in children with airway foreign bodies. 7,8The use of either succinylcholine or a nondepolarizing neuromuscular drug would have complicated this child’s recovery and potentially might have led to a further delay in his diagnosis and treatment.

Juvenile myasthenia gravis, like adult forms of the disease, is a prototypical autoimmune disorder. 1–5,9The presence of acetylcholine receptor antibodies in most patients, passive transfer symptoms of the disease associated with antibodies, and the improvement in condition that occurs when antibody titers decrease are evidence of the autoimmune origin. 3–5Plasmapheresis is frequently used preoperatively to reduce antibody titers and ameliorate disease symptoms. 9–11Thymectomy can produce a long-lasting remission of symptoms in many patients with this illness. 12,13Thymectomy was initially reserved for patients with thymoma and thymic hyperplasia, but early thymectomy results in remission in almost 50% of patients with JMG, compared to 10–20% remission in children who receive medical therapy. 1,12,13The rapid recovery and lesser surgical morbidity associated with cervical thymectomy compared to sternal thymectomy are additional reasons that many pediatric neurologists favor early thymectomy in children with JMG. 1,13 

In summary, this report highlights the need to consider a neurologic or neuromuscular disease in patients with foreign body aspiration. This child’s clinical presentation and response to treatment indicate some of the differences in presenting symptoms and signs and response to thymectomy in JMG compared with adult-onset myasthenia gravis.