Rinsho Shinkeigaku (Clinical Neurology)

Case Report

A case of anti-MuSK antibody-positive myasthenia gravis with dropped head as the initial presenting symptom

Tomoko Okano, M.D.1), Junko Fujitake, M.D.1), Kaori Suzuki, M.D.1)2), Nobuhito Mori, M.D.1), Masanobu Sonobe, M.D.1), Kiyoe Ohta, Ph.D.3), Shunya Nakane, M.D.4) and Kyoko Saida, M.D.1)

1)Department of Neurology, Kyoto City Hospital
2)Department of Neurology, Tottori Prefectural Central Hospital
3)Clinical Research Center, Utano National Hospital
4)Department of Neurology, Tokushima University Faculty of Medicine

A 53-year-old woman was admitted to our hospital because of dropped head. Neurological examination showed no abnormality except for weakness of the neck extensor muscles. Her symptoms worsened in the evening, requiring her to support her head by placing her hand against her chin. Edrophonium and repetitive stimulation tests gave negative results, and anti-acetylcholine receptor antibodies were not detected. She had no thymoma. However, she was found to have a high serum titer of anti-MuSK antibody (37.3 nM). She was diagnosed as having myasthenia gravis (MG) and treatment with pyridostigmine was started. However, this had to be withdrawn because of fasciculation as an adverse effect. She was therefore treated with prednisolone, and this resulted in marked improvement. The initial presenting symptom in this case was dropped head, and there were none of the results of laboratory or electrophysiological examinations that are usually typical of MG. MG was eventually diagnosed by measurement of anti-MuSK antibody. The present case suggests that a patient presenting with dropped head without any obvious cause needs to be studied for the presence of anti-MuSK antibody.

(CLINICA NEUROL, 46: 496|500, 2006)
key words: myasthenia gravis, muscle-specific tyrosine kinase, anti-MuSK antibody, dropped head, seronegative MG

(Received: 17-Dec-05)