Childhood-onset myasthenia gravis with thymoma

Juvenile myasthenia gravis is an acquired, autoimmune disease occurring before age 16 years. Thymoma is exceedingly rare in children, especially in association with juvenile myasthenia gravis. We describe a 14-year-old boy with juvenile myasthenia gravis and thymoma. He presented with difficulties chewing and swallowing, nasal speech, and fluctuating weakness of the leg muscles. Neurologic examination revealed masticatory and bulbar muscle weakness with nasal speech, proximal muscle weakness, fatigability of the arms and legs, and distal muscle weakness of the legs. A diagnosis of juvenile myasthenia gravis was confirmed by a positive neostigmine test, a decremental response on repetitive nerve stimulation, and increased titers of serum anti-acetylcholine receptor antibodies. The patient received anticholinesterases, corticosteroids, azathioprine, and thymectomy. A pathohistologic analysis of the thymus gland indicated thymoma, Masaoka grade II. After 2 years of an unstable disease course, remission was achieved. Because only 10 cases of thymoma-associated myasthenia gravis are described in the pediatric population, this report offers an important contribution to a better understanding of this rare association.