One-and-a-Half Syndrome With Facial Diplegia: The 15 1/2 Syndrome?

Abstract

We recently examined a 67-year-old man who demonstrated findings consistent with a unilateral one-and-a-half syndrome and a bilateral lower motor neuron facial palsy (1 1/2 + 7 + 7 = 15 1/2). The patient had the sudden onset of dizziness, nausea, and blurring of vision. He smoked heavily and had a history of diabetes mellitus. Examination disclosed a complete right horizontal conjugate gaze palsy and a right adduction deficit. Oculocephalic stimulation did not improve the defective eye movements. Convergence was relatively spared. Vertical ocular movements and alignment were normal and ptosis was absent. The pupils were equal in size and normally reactive to light and a near stimulus. The remainder of the neurologic examination was normal. One day later, a bilateral lower motor neuron facial palsy abruptly developed, including bilateral flattening of the nasolabial fold and absent forehead wrinkling. Brain computed tomography was normal. FLAIR and T2-weighted brain magnetic resonance imaging disclosed high signal in the lower pontine tegmentum, findings considered typical of stroke (Fig. 1). A facial nerve conduction and blink reflex study confirmed a bilateral lower motor neuron facial palsy.FIG. 1: Axial FLAIR (A), axial T2-weighted (B), sagittal T2- weighted (C), and diffusion-weighted (D) magnetic resonance images show increased signal (arrow) consistent with ischemic stroke in the paramedian dorsal pontine tegmentum bilaterally.When last examined 2 months after the onset of symptoms, the patient showed only a minimal deficit in right horizontal gaze. Horizontal gaze palsy in one-and-a-half syndrome may result from lesions in the abducens nucleus, in the abducens nerve and the medial longitudinal fasciculus, or in the pontine paramedian reticular formation (PPRF) (1,2). Isolated PPRF lesions are associated with retained vestibulo-ocular movement. If the vestibulo-ocular movement is abolished, the lesion lies rostral or caudal to the PPRF (5,6). Because our patient showed limitation of oculocephalic abduction toward the right side, we presume that the lesion lies in the abducens nucleus or fascicle rather than in the PPRF (2-7). More rapid resolution of ipsilateral adduction compared with abduction favors involvement of the abducens fascicle rather than the nucleus. An alternative hypothesis is that these findings reflect the relative vulnerability of abducens motor neurons innervating the lateral rectus (2). The one-and-a-half syndrome is rarely an isolated finding (7), being usually associated with cranial nerve palsies (facial in 75%), hemiplegia (30%), or hemihypesthesia (35%) (3,4). A lower motor neuron facial nerve palsy is the most commonly associated finding, resulting from involvement of the genu of the intraaxial fasciculus of the facial nerve in the pontine tegmentum (2,4). Although the combination of a one-a-a-half syndrome and an ipsilateral seventh nerve palsy has been described ("eight-and-a-half syndrome" (2)), we are unaware of a previous description of a one-and-a-half syndrome with bilateral seventh nerve palsies, as our patient had. We attribute these findings to a bilateral tegmental pontine lesion involving the right abducens nucleus or fasciculus, bilateral or right medial longitudinal fasciculus, and bilateral intraaxial fasciculi of the facial nerve (Fig. 2). The histopathologic studies of Fisher (8) showing terminal bifurcation of a single paramedian artery to supply the dorsal pontine tegmentum bilaterally could explain why occlusion of a single vessel would produce these findings.FIG. 2: Schematic axial section through the caudal pons. The shaded area represents the site of the lesion that involves the right abducens nucleus, both medial longitudinal fasciculi, and both seventh (facial) nerve fasciculi.Jong Seok Bae, MD Hong Ki Song, MD Department of Neurology; Seoul Medical Center and College of Medicine, Hallym University; Seoul, Korea; E-mail: [email protected]