A previously healthy 8-year-old girl presented with bilateral ptosis and impaired superior gaze. She was transferred from an urgent care center to the emergency department for advanced brain imaging after abnormal extraocular movements were detected by the doctor.
The patient’s father said he had noticed that his daughter had trouble fully opening her eyes for about a month. He said these symptoms seemed less noticeable in the morning, but she would be symptomatic by the time she got home from school.
The patient said the only way she could look up was to look up. No head trauma or history of autoimmune disease in the family has been reported. His father said he did not practice canning or pickling.
The girl’s vital signs were normal and she seemed comfortable with no respiratory distress. She had bilateral ptosis with diplopia on visual acuity tests that worsened at the extremes of gaze. An extraocular movement assessment revealed more upward gaze impairment in his left eye than in his right. Applying an ice pack to his eyelids for 120 seconds improved his symptoms. What is the diagnosis?
Find the case discussion on the next page.
Diagnosis: variant of juvenile myasthenia gravis
This patient’s symptoms of bilateral ptosis and diplopia with progressive symptoms throughout the day suggested myasthenia gravis. Her symptoms only involved her eyes, suggesting the mildest variant of juvenile myasthenia gravis, called ocular myasthenia gravis. (Children’s Hospital of Philadelphia; https://bit.ly/3sTtapk.)
It is important when considering this diagnosis to explore other muscle groups, especially bulbar muscles of the head and neck (which may present as dysarthria or dysphagia) and respiratory muscles (dyspnea which worsens in the evening or after prolonged exertion).
Myasthenia gravis is a neuromuscular disease of autoimmune etiology. The pathophysiology involves autoantibodies directed against the acetylcholine receptor (AChR) present at the motor endplate or an AChR-associated tyrosine kinase called muscle-specific tyrosine kinase. (F1000Res. 2016;5:F1000 Faculty Rev-1513; https://bit.ly/3hMSF5l; Indian J Ophthalmol. 2014;62:985; https://bit.ly/3J1gvq4; Muscular nerve. 2011;44:36; https://bit.ly/3CmV2VQ.) As expected, impaired AChR function leads to muscle weakness and rapid muscle fatigue.
Treatment aims to increase the concentration of acetylcholine in the synaptic cleft using acetylcholinesterase inhibitors to slow the breakdown of acetylcholine. (Children’s Hospital of Philadelphia; https://bit.ly/3sTtapk; Up to date. March 29, 2021; https://bit.ly/3KpdEHw.) This is also the mechanism by which the ice pack test produces its effect, and emergency physicians can perform this inexpensive and readily available maneuver at the bedside. An improvement of 2 mm or more in the enlargement of the palpebral fissure is considered a positive test. (JRSM Short Representative. 2010;1:14; https://bit.ly/34sKnfV.)
Performing this test involves the doctor measuring the palpebral fissure, then placing an ice pack over the eyes for 120 seconds before obtaining a second measurement of the palpebral fissure. (JRSM Short Representative. 2010;1:14; https://bit.ly/34sKnfV.) The preferred pharmacological test is to administer neostigmine 1.5 mg IM (adult dose) with an onset of about 20 minutes. (BMJ Case Rep. 2011;2011:bcr0420114066; https://bit.ly/3vSrH4C.) Administration is useful in diagnosing myasthenia gravis given its short duration of action.
The edrophonium test was previously used, but this drug has not been available in the United States since 2018. Negative measurement of inspiratory force/forced vital capacity can help detect respiratory muscle involvement. An anti-acetylcholine receptor antibody test can be used to distinguish myasthenia gravis from other conditions such as chronic muscle fatigue and weakness. The muscle-specific tyrosine kinase antibody test is used in patients with symptoms suggestive of myasthenia gravis when the anti-acetylcholine receptor antibody test is negative.
A differential diagnosis for a patient without known myasthenia gravis should include exposure to botulinum toxin, Horner’s syndrome, elevated ICP, and intracranial mass. Physicians should perform a prompt assessment of myasthenic crisis in people with known or suspected myasthenia gravis; this complication involves marked weakness of the respiratory muscles leading to respiratory distress. (Neurohospitalist. 2011;1:16; https://bit.ly/3HPqQUp.) Patients in myasthenic crisis will present in respiratory distress and often require urgent airway management. Patients should be admitted for further workup, trial of an acetylcholinesterase inhibitor, and initiation of pyridostigmine for daily symptoms.
Our patient was admitted to the pediatric ward for MRI imaging to rule out an intracranial mass, and he demonstrated no mass or lesion. A chest MRI assessed the thymoma, which was not present. (Autoimmune disease. 2011;2011:474512; https://bit.ly/362ZWLA.) She was also evaluated by the pediatric neurology team, which provided a presumptive diagnosis of juvenile myasthenia gravis.
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Dr Maurantoniois a second-year emergency medicine resident at the Denver Health Residency in Emergency Medicine. Read the quick reference columns athttp://bit.ly/EMN-QuickConsult.