The other two types of the neuromuscular disease that primarily affect pediatric patients are congenital MG, which can begin any time from birth into adulthood, and transient neonatal MG, which typically affects babies.
Juvenile MG, which usually begins before age 18, is a rare, chronic condition that often manifests as a lifelong autoimmune disorder. The disease is relatively uncommon in Europe and North America, and is more likely to be seen in Asian populations, particularly in children and teens under the age of 15. In many Asian patients, the symptoms are restricted to the eye and eyelid muscles, as seen in patients with ocular MG.
Like MG in adults, this juvenile form of the disease is associated with the presence of self-reactive antibodies targeting and damaging proteins involved in nerve-muscle communication, which in turn leads to muscle weakness.
Unlike adults, however, children and adolescents are less likely to test positive for self-reactive antibodies targeting the acetylcholine receptor (AChR) — the most common autoantibodies seen in grownups with MG. This is especially true for younger patients who develop the condition before reaching puberty.
Many patients with juvenile MG also have abnormalities in the thymus — a gland that is part of the immune system and thought to trigger or help sustain the production of the harmful self-reactive antibodies that drive MG.
Thymus enlargement — a condition known as thymus hyperplasia — is the most common thymus abnormality seen in these younger patients. Conversely, thymus tumors (thymomas) are rare, particularly in children who develop MG before reaching puberty.
Symptoms of juvenile MG can start gradually and may be difficult to recognize at first. Because it is a rare disease, and its symptoms are shared with a number of other illnesses, it may take time for doctors to make a proper diagnosis.
The most typical symptoms are similar to those seen in adults. These include experiencing eyelid droopiness and/or double vision, tiring easily, and having difficulties eating and swallowing. Some children also experience shortness of breath, speech impairment, or changes in facial expression.
When MG starts before a child reaches puberty, it is commonly restricted to muscles controlling eye and eyelid movements. When it strikes youngsters who have already reached puberty, it often manifests as generalized muscle weakness affecting other muscle groups, much like what is seen in generalized MG.
Treatment and prognosis
Cholinesterase inhibitors like Mestinon (pyridostigmine) are often the first-line of treatment for juvenile MG and may be sufficient in patients with purely ocular disease symptoms or mild generalized disease.
Other medications like corticosteroids and immunosuppressive agents also have been used in children with refractory disease, but some of their side effects have limited their use in these patients. Plasmapheresis and intravenous immunoglobulin (IVIg) also may be used, particularly in the context of severe disease flare-ups or myasthenic crises.
Surgical removal of the thymus — a procedure called thymectomy — is usually not recommended for treating children who develop MG before reaching puberty. However, surgery may be beneficial for those with generalized disease who fail to respond to cholinesterase inhibitors or immunosuppressants.
In general, the long-term prognosis of younger patients with juvenile MG is good. Children with the condition — especially those who develop the disease before puberty — have higher rates of disease remission compared with adults.
Last updated: Nov. 11, 2021
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