Pediatric neurologist Tom Crawford, a nationally recognized expert on myasthenia gravis and other neuromuscular disorders, discusses the causes, diagnosis and treatment of the condition in children.
How would you describe myasthenia gravis?
Myasthenia gravis is a chronic autoimmune disorder that causes weakness in the skeletal muscles, including those that control eye movement and facial expression, chewing, talking and breathing. It is mostly an adult disease but it does reach down into kids and sometimes very young kids. When it does affect children, it can be particularly devastating.
What causes the disease?
The culprit is an error in the transmission of nerve impulses at the neuromuscular junction, where nerve cells connect with muscles. Specifically, antibodies block, alter or destroy the receptors for the neurotransmitter acetylcholine, preventing the muscle from contracting.
What are the signs and symptoms of myasthenia gravis?
Drooping eyelids, slurred speech, difficulty eating, and weakness in the arms, hands, fingers, legs and neck. The major issues of concern are changes in the quality of the child’s voice and difficulty swallowing. This disease is notable for the distinction between fatigue and weakness. The person can be normally strong for a while, and then their muscle power gives way and they become profoundly weak, even to the point where their breathing and swallowing muscles become disabled.
If parents see such signs, what should they do?
Their child’s pediatrician is a good first stop but they will likely need to consult with a pediatric neurologist with deep experience diagnosing and treating the disease. This is an area where expertise matters. Myasthenia gravis can range from a relatively minor condition to a potentially fatal disease, one we have to be extremely aggressive in treating.
How do you diagnose it?
Through physical and neurologic examinations, we check the patient’s muscle strength and tone, coordination, and sense of touch. A blood test may reveal elevated levels of acetylcholine receptor antibodies, and we can detect impaired nerve-to-muscle transmission through single fiber electromyography, or EMG. A pulmonary function test can help predict when the muscles that control breathing will weaken to the point where patients require a ventilator. Here at Johns Hopkins Children’s Center, we developed a novel but simple “slurp test,” which has become the standard in identifying patients at risk of respiratory failure.
A slurp test?
We ask the patient, using a straw, to make a slurp sound by sucking 4 ounces of water out of a cup. Every kid wants to make a slurp sound, but for kids who have myasthenia, the ability to suck water through a straw is like sucking a milk shake through a straw. Your muscles start to hurt and soon you cannot do it. If that happens with water, it may be a sign that you are getting close to not being able to breathe.
How do you treat it?
We administer medications to slow the breakdown of acetylcholine, improving neuromuscular transmission and increasing muscle strength. Immunosuppressive drugs like prednisone improve muscle strength by suppressing the production of abnormal antibodies, but they can cause significant side effects. Another treatment, plasmapheresis, removes harmful antibodies in plasma and replaces them with good plasma.
Is surgery an option for myasthenia gravis?
Research has shown that in patients with myasthenia gravis the thymus gland may give incorrect instructions to developing immune cells, causing the immune system to attack its own cells and produce these acetylcholine receptor antibodies. Stable or long-lasting complete remissions are the goal of surgically removing the thymus, and may occur in 50 percent of patients.
What’s the prognosis for patients with myasthenia gravis?
Most kids respond to therapy, significantly improve their muscle strength and lead normal lives.