One and a Half Syndrome Shirley H. Wray, M.D., Ph.D. Professor of Neurology, Harvard Medical School Director, Unit for Neurovisual Disorders Massachusetts General Hospital

The One-and-a-Half Syndrome On horizontal gaze there is: An ipsilateral gaze paresis or palsy An internuclear ophthalmoplegia (INO) on contralateral gaze At rest, the eyes are: Orthophoric, or, in acute stage Ipsilateral eye esotropic or Contralateral eye exotropic (Paralytic pontine exotropic)

Three possibilities to account for an ipsilateral horizontal gaze palsy: may be due to unilateral lesion affecting The ipsilateral PPRF only The ipsilateral abducens nucleus alone Both the ipsilateral PPRF and abducens nucleus

Abducens Nucleus All the cells necessary for ipsilateral horizontal gaze: Motoneurons whose axons form the sixth nerve (VIN) to innervate the ipsilateral lateral rectus muscle Internuclear neurons which send axons across the midline to opposite MLF and ultimately to the medial rectus motoneurons in the contralateral oculomotor nucleus (III N).

Pathogenesis of Certain Signs Ocular Motor Possible Pathophysiologic Deficit Substrate Ipsilateral adduction weakness Ipsilateral slowed abducting saccades Contralateral abduction nystagmus Interruption of axons of abducens internuclear motoneurons Inadequate inhibition of medial rectus motoneurons Impaired inhibition of contralateral medial rectus or Interruption of descending fibers to contralateral abducens nucleus or Involvement of adjacent PPRF

Neurology 1983; 33:

ReportedBostonTotal casesseries Brainstem Infarct Multiple Sclerosis Pontine Glioma 213 Arteriovenous Malformation 101 Pontine Hemorrhage 808 Basilar Artery Aneurysm 011 Cerebellar Astrocytoma 202 Metastatic Melanoma 101 Ependymoma Fourth Ventricle Table 1. The one-and-a-half syndrome: Etiology

Diplopia12 Blurred Vision8 Oscillopsia4 Difficulty looking to one side2 “Quivering” of the eye1 No visual complaint3 Table 2. One-and-a-half syndrome (N = 20): Visual Symptoms

(N = 20) Gaze-evoked upbeat nystagmus12 Skew deviation8 Horizontal ipsilateral gaze nystagmus4 Rotary component to horizontal ipsilateral gaze nystagmus2 Spontaneous nystagmus to the contralateral side1 Absent or impaired convergence5 Saccadic vertical pursuit9 Gaze-evoked downbeat nystagmus4 Impaired upward gaze1 (N = 11) Exotropia4 Esotropia3 Orthotropia4 Table 3. One-and-a-half syndrome (N = 20;11): Associated ocular motility signs

Cranial Nerve Involvement I0 II1 III0 V3 VII4 VIII2 IX3 XI0 XII2 Horner’s Syndrome1 Weakness or spasticity6 Sensory deficits7 Abnormally brisk or asymmetric reflexes5 Extensor plantar responses9 Incoordination10 Table 4. One-and-a-half syndrome (N = 20): Associated neurologic signs

Esotropia of the ipsilateral eye

Patient 1. The one-and-a-half syndrome (A) Mild left INO looking right. (B) Esotropia OS (ipsilateral) in the primary position of gaze. (C) Horizontal conjugate gaze palsy attempting to look left. (D) Normal convergence.

Paralytic Pontine Exotropia

Patient 2. Paralytic pontine exotropia. (A) Horizontal conjugate gaze paresis looking right. (B) Exotropia OS (contralateral) in the primary position of gaze. (C) Right INO looking left. (D) Right “peripheral-type” ipsilateral facial palsy. (E) Impaired convergence.

Patient 2. Paralytic Pontine Exotropia A.Horizontal conjugate palsy looking right. B.Exotropia OS contralateral in the primary position of gaze. C.Right INO looking left D.Right “peripheral-type” ipsilateral facial palsy E.Impaired convergence

In paralytic pontine exotropia the exotropic eye shows: Abduction nystagmus during attempts to move it laterally Extreme slowness of adduction saccades when eye fixing to move it to the midline

Paralytic Pontine Exotropia attributed to: Tonic contralateral deviation of the eyes Implies acute ipsilateral PPRF lesion Failure of ipsilateral eye to deviate medially explained by the INO

Paralytic pontine exotropia OS

Paralytic pontine exotropia right horizontal gaze palsy