[A case of elderly-onset myasthenia gravis mimicking stroke with dysarthria and left upper extremity paresis].

An 80-year-old woman presented with sudden-onset dysarthria and left-side dominant quadriparesis and transferred to our hospital. A neurologic examination revealed slurred speech, prominent left upper extremity weakness and mild weakness of the other extremities. Brain MRI revealed a history of right-side cerebral artery bypass surgery, but no new lesions indicative of stroke. Left upper extremity weakness had improved soon after admission, so a transient ischemic attack was suspected. After admission, the dysarthria fluctuated. The patient's respiratory condition deteriorated several days later and she required ventilation support. Assessment of the cause of the respiratory failure revealed positive muscle-specific kinase (MuSK) antibodies, which suggested myasthenia gravis (MG). The symptoms gradually improved with immunotherapy and we were able to completely withdraw her from the ventilator after a few months. There were some reports that dysphagia and dysarthria present suddenly like stroke without fluctuation of symptoms in elderly-onset MG. It is necessary to note that MG diagnosis may be difficult if elderly patients have multiple comorbidities and unclear diurnal fluctuations.