[Midbrain ptosis with diurnal fluctuation like myasthenia].

A 51-year-old man was admitted because of bilateral fatigable blepharoptosis with diurnal fluctuation. He had a tendency to take much instant foods before onset. On admission, he showed symmetrical bilateral ptosis, supranuclear upward gaze palsy and vertical diplopia. Ptosis mildly improved on lateral or upward gaze. Bell's phenomenon and pupillary response were intact. Intravenous edrophonium infusion test and serum antiacetylcholine receptor antibody were negative. Cranial MRI and CT demonstrated the lesion in the periaqueductal gray (PAG) region from superior colliculus to upper pontine level, which was remarkably enhanced by Gd-DTPA infusion. He was diagnosed as midbrain ptosis, probably due to atypical Wernicke's encephalopathy. It was conceivable that the PAG lesion might be contributory to fatigable blepharoptosis (pseudomyasthenia) and supranuclear upward gaze palsy in the present case, because the PAG controls levator palpebrae neurons of central caudal nucleus in oculomotor nucleus complex and receives afferents from the limbic system., reticular formation and posterior commissure.