For many years the EmergiQuiz presentations have been one of the highlights of the AAP National Conference and Exhibition Section on Emergency Medicine Program. Pediatric Emergency Medicine Fellows present challenging cases and another fellow attempts to make the diagnosis. This is followed by an educational presentation that focuses not just on the rare diagnosis, but also the general learning inherent to the case. This post highlights a recent EmergiQuiz case.
The original EmergiQuiz case was submitted by Joshua Haverland and Gena Schubert from Phoenix Children’s Hospital, and was entitled, “How Much Drool is Too Much Drool.”
The cardinal feature of myasthenia gravis is fluctuating skeletal muscle weakness including ocular, bulbar, and respiratory muscle involvement. The symptoms most commonly are worse later in the day or after exertion.
Though respiratory muscle function gets all the press, and rightfully so – ocular function can be an early sign that is easily missable. Think about how many times have you written “pupils are equal round and reactive to light” and “extraocular muscles are intact” in your note? What if a patient has ptosis, do you fully assess lid elevation? Ask to see a recent picture of the child for comparison? Teasing out early ocular involvement especially can be challenging.
The weakness is from the antibody mediated T cell response to acetylcholine receptors or receptor associated proteins at the postsynaptic neuromuscular junction. Remember to get a good history of any new medications that can be a cause or recent illness. Drugs most often associated are antibiotics (aminoglycosides, fluoroquinolones, erythromycin, azithromycin), cardiac drugs (beta blockers, procainamide, quinidine), and magnesium. Another important cause is an underlying thymoma.
Initial management of myasthenic crisis
Myasthenic crisis occurs when respiratory muscle weakness is involved leading to respiratory distress and requires respiratory support. The diagnosis of myasthenia gravis is complex. Bedside tests including the ice pack test and edrophonium test are sensitive but have major limitations with false positive results. Thus, a confirmatory test with auto antibiodies and electrophysiological studies (repetitive nerve stimulation studies and single-fiber electromyography) are needed. Patients who have detectable antibodies to the acetylcholine receptor (AChR) or to the muscle-specific receptor tyrosine kinase (MuSK) are considered to have seropositive myasthenia gravis.
Ask your Respiratory Therapist to measure a NIF – negative inspiratory force (AKA maximum inspiratory pressure) – to help assess declining function. NIF measures inspiratory muscle strength and is when a patient inhales as hard as they can with measurement of the negative pressure that they generate. MEP – Maximal Expiratory Pressure – is the opposite of the NIF. The maximum positive pressure the patient can generate assesses expiratory muscle strength and correlates with ability to cough and clear secretions.
How do we fix it?
ABCs! The treatment for myasthenia gravis begins with respiratory support including intubation or non-invasive ventilation. Don’t intubate just because the NIF is abnormal (-30 in an adult sized patient). Remember that drug Physostigmine? Symptomatic treatment with acetylcholinesterase inhibition increases the amount of acetylcholine at the neuromuscular junction and thus can improve the symptoms. Steroids and nonsteroidal immunosuppressive agents target immune dysregulation. Likewise, plasma exchange or intravenous immune globulin (IVIG) are immunomodulation treatments used for myasthenia gravis.
The Bottom Line
Myasthenia gravis along with myasthenic crisis is an uncommon yet important diagnosis to keep on the differential of a patient with respiratory distress, especially in a patient with ptosis and sialorrhea. Early recognition and consultation with Pediatric Neurology and consideration for ICU admission can help with diagnosis and treatment.
Gilhus NE. Myasthenia Gravis. N Engl J Med 2016; 375:2570.
Mehrizi M, Fontem RF, Gearhart TR, Pascuzzi RM. Medications and Myasthenia Gravis (A Reference for Health Care Professionals), Indiana University School of Medicine (Department of Neurology), 2012.