A misdiagnosed myasthenia gravis with anti-muscle-specific tyrosine kinase antibodies with possible childhood onset.

INTRODUCTION: Childhood onset myasthenia gravis associated with anti-muscle-specific tyrosine kinase antibodies is very rare and atypical in presentation. CASE REPORT: As a baby, the pre- sented patient was choking and sleeping with open eyes. She had weak cry and breathing difficulties. In childhood, there were fre- quent falls and fluctuating swallowing difficulties. At the age of 19 she was misdiagnosed with Miller Fisher syndrome due to the presence of diplopia, ataxia and hyporeflexia with spontaneous recovery. Repetitive nerve stimulation test was normal. Four years later, after several relapses, there was significant decrement on facial muscles. Neostigmine test was negative, provoking muscle fasciculations. Serum anti-muscle-specific tyrosine kinase antibodies were positive. With cyclosporine therapy she achieved the minimal manifestations status. CONCLUSION: The presented case confirms that childhood onset myasthenia gravis associated with anti-muscle-specific tyrosine kinase antibodies is often with atypical presentation and spontaneous remissions, so it could be easily misdiagnosed.

Myopathy, muscle atrophy and tongue lipid composition in MuSK myasthenia gravis.

Myasthenia gravis (MG) associated with anti-muscle-specific tyrosine kinase (MuSK) antibodies differs in many aspects from typical presentation of acetylcholine receptor (AChR)-positive MG. Myopathy and muscle atrophy are observed in MuSK-positive MG patients, unlike AChR-positive patients with MG. That is why the aim of this study was to assess the presence of myopathy and muscle atrophy as well as the tongue lipid composition in our cohort of MuSK-positive MG patients. Clinical examination, electromyography (EMG) and proton magnetic resonance spectroscopy were performed in 31 MuSK-positive and 28 AChR-positive MG patients. Myopathic EMG was more frequent in MuSK compared to AChR MG patients. In AChR MG patients, myopathic EMG in facial muscles was more frequent after long-term corticosteroid treatment, which was not the case with MuSK-positive MG patients. Facial and/or tongue muscle atrophy was registered in 23 % of MuSK MG patients. Longer disease duration was observed in patients with clinical signs of tongue and/or facial muscle atrophy compared to those with normal tongue muscle. Intramyocellular lipid deposition in the tongue was present in 85.2 % of MuSK and 20 % of AChR MG patients. Female MuSK MG patients had more frequently electrophysiological signs of myopathy on the facial muscles and signs of intramyocellular lipid deposition in the tongue, compared to male patients with MuSK-positive MG. Myopathy, muscle atrophy and intramyocellular lipid deposition in the tongue are more frequent in MuSK-positive compared to AChR-positive MG patients.

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.