[A case of myasthenia gravis presenting solely with bulbar palsy unassociated with easy fatigability]

A 69-year-old Japanese female was admitted because of progressive nasal voice and dysphagia. Neurological examination revealed paresis of the soft palate with marked dysphagia and rhinolalia. Otherwise there was no weakness or easy fatigability in extraocular muscles and extremities. On laboratory test, anti-acetylcholine receptor antibody (anti-AChR Ab) was positive, while anti-muscle-specific tyrosine kinase antibody (anti-MuSK Ab) was negative. Edrophonium test was positive, resulting in clear improvement in phonation and swallowing. Harvey-Masland test of ocular and extremity muscles did not show any waning. With the diagnosis of bulbar myasthenia gravis, the patient was treated with methylprednisolone and pyridostigmine, resulting in clear improvement of the symptoms. The present case shows that it is important to consider MG even in cases presenting solely with progressive bulbar palsy without easy fatigability. So far, cases of bulbar myasthenia gravis with positive anti-MuSK Ab have often been reported. As shown in the present case, bulbar myasthenia gravis can also be associated with positive anti-ACh-R Ab but negative anti-MuSK Ab.