“Sixteen and a half”: a novel pontine neuro-ophthalmological syndrome

Abstract

Two neuro-ophthalmological syndromes due to paramedian pontine infarction have previously been described. The ‘‘one and a half’’ syndrome was first reported and named by Miller Fisher [1], and consists of horizontal gaze palsy combined with an ipsilateral inter-nuclear ophthalmoplegia (INO) resulting in loss of all horizontal eye movements except abduction of the contralateral eye. The causative lesion is usually within the ipsilateral pontine tegmentum and is due to involvement of the abducens nucleus plus the medial longitudinal fasciculus (MLF), or alternatively to involvement of the MLF plus the paramedian pontine reticular formation (PPRF). These structures lie in close proximity to the nucleus and intra-axial fasiculus of the facial nerve. Consequently, ipsilateral fascicular lower motor neurone facial nerve palsy may accompany the ‘‘one-and-a-half’’ syndrome. This situation was named the ‘‘eight and a half syndrome’’ by Eggenberger [2], who reported 3 cases of this syndrome that had occured secondary to ischaemic stroke. In continuation of this concept, we here describe the ‘‘sixteen and a half syndrome’’, which is the ‘‘one and a half’’ syndrome with an additional 7th and 8th cranial nerve (vestibulo-cochlear nerve) palsy. A 78-year-old right-handed man presented with sudden onset of incomplete right upper limb paresis, horizontal diplopia and ataxia. This was shortly followed by complete right lower limb paresis. There was associated nausea and vomiting. Examination revealed a left-sided lower motor neurone facial nerve palsy and dysarthria with loss of conjugate gaze to the left and loss of adduction of the left eye. Abduction of the right eye was accompanied by horizontal nystagmus. Convergence was spared. The patient also complained of new-onset left-sided hearing loss. The patient and his family were certain that his hearing before this event had been normal. Magnetic resonance imaging (MRI) with diffusion-weighted sequences revealed an area of restricted diffusion consistent with an acute infarct. The lesion extended beyond and lateral to the paramedian pontine territory supplied by the anteromedial group of pontine perforating arteries, and dorsally to the fourth ventricle and the region of the facial colliculus (Fig. 1a, b). Pure tone audiometry showed no detectable hearing in the left ear. Brainstem auditory evoked potential testing showed no reproducible wave I, wave III or wave V after left ear stimulation. Waves I, III and V from right ear stimulation were of low amplitude with normal absolute and interwave latencies. Eight months later, the Weber test lateralized to the right ear, and the Rinne test revealed absent air-conducted and bone-conducted sound perception in the left ear. Our patient had an ‘‘eight and a half’’ syndrome plus additional ipsilateral hearing loss. We name this clinical entity the ‘sixteen and a half syndrome’. Hearing loss has not previously been described in association with either ‘‘one and a half’’ or ‘‘eight and a half’’ syndrome. A clinical series of 20 cases of ‘‘one and a half’’ syndrome noted G. Cummins R. Dunne K. O’Rourke (&) T. Lynch Dublin Neurological Institute, Mater Misericordiae University Hospital, 57 Eccles St., Dublin 7, Ireland e-mail: killian.orourke@gmail.com