Sudden onset diplopia in an elderly male patient : answer

Abstract

Brain diffusion-weighted imaging revealed a small hyperintense lesion involving the median dorsal midbrain (Fig. 1). Aspirin and clopidogrel were prescribed. He was discharged 8 days after onset, at which point his diplopia was slightly improved. Binocular double vision suggests the dysfunction of extraocular muscles, the neuromuscular junction, cranial nerves, cranial nerve nuclei, or internuclear and supranuclear connections [1]. Accurate localization of the underlying lesion is the first step towards the correct diagnosis. Each extraocular muscle is innervated by the corresponding cranial nerve, which originates from the individual cranial nerve nucleus. In complete oculomotor nerve palsy, there is ptosis due to the dysfunction of the levator palpebrae superioris muscle. The eye is deviated down and out, with impaired elevation, depression, and adduction. Pupil involvement usually indicates a compressive lesion, while sparing of the pupil is more likely due to ischemia [1]. The oculomotor nucleus is a paired structure that is located in the midbrain, adjacent to the medial longitudinal fasciculus (MLF) and reticular formation, ventral to the aqueduct of Sylvius and the fourth ventricle. The oculomotor nucleus lesion typically causes ipsilateral ophthalmoparesis and pupil dilatation with bilateral impairment of ocular elevation and bilateral ptosis. Isolated weakness of a single muscle is possible with an oculomotor nucleus lesion and isolated bilateral oculomotor nuclear palsy is extremely rare [2]. Classic signs of internuclear ophthalmoplegia (INO) are the impairment of adduction of the ipsilateral eye and the preservation of abduction of the contralateral eye when the patient tries to gaze in the contralateral direction [3]. It is induced by a lesion involving the MLF in the brainstem. One-and-a-half syndrome consists of lateral gaze palsy in one direction and INO in the other direction with a contralateral gaze. It occurswith lesions in the dorsal pontine tegmentum that impair both the ipsilateral paramedian pontine reticular formation or the abducens nucleus and the ipsilateralMLF.