What is the diagnosis and treatment for Eight-and-a-half syndrome?

Eight-and-a-Half Syndrome

Definition and Clinical Presentation

Eight-and-a-half syndrome is a rare neuro-ophthalmologic condition consisting of ipsilateral horizontal gaze palsy, internuclear ophthalmoplegia (INO), and ipsilateral lower motor neuron facial nerve palsy, caused by a localized lesion in the dorsal pontine tegmentum. 1, 2

The syndrome represents a combination of:

• One-and-a-half syndrome (conjugated horizontal gaze palsy plus INO) 3
• Ipsilateral fascicular cranial nerve VII palsy 3

Specific Clinical Features to Identify

On examination, you will find:

• Limitation of horizontal eye movement in the ipsilateral eye (affected side cannot abduct) 1
• Limited adduction of the contralateral eye when attempting to look toward the lesion side 1
• Ipsilateral lower motor neuron facial weakness affecting the entire half of the face 1, 2
• Preserved vertical eye movements (distinguishes this from more extensive brainstem pathology) 3

Anatomical Localization

The syndrome has precise localizing value to the dorsal tegmentum of the pons, specifically involving three adjacent structures: 1, 2

• The abducens nucleus or paramedian pontine reticular formation (PPRF) 2
• The ipsilateral medial longitudinal fasciculus (MLF) 2, 3
• The facial nerve fascicle at the facial colliculus 3

Diagnostic Workup

Immediate Imaging

MRI of the brain with diffusion-weighted imaging is the diagnostic modality of choice to identify the pontine lesion. 1, 2

Typical MRI findings include:

• T2 hyperintense lesion in the dorsal pons adjacent to the fourth ventricle 4, 2
• Acute infarct on diffusion-weighted imaging in the posterior pontine tegmentum 2, 3
• Small, circumscribed lacunar infarction pattern in most cases 3

Additional Evaluation

• Vascular risk factor assessment: hypertension, diabetes mellitus, hyperlipidemia 1, 2
• Stroke workup: carotid imaging, echocardiography, cardiac monitoring for arrhythmias 2
• Consider demyelinating disease if patient is younger (<50 years) or has atypical features 4

Etiology

Most Common Cause

Acute brainstem infarction is the most frequent etiology, typically presenting as a small lacunar stroke in the dorsal pons. 1, 2, 3

Alternative Etiologies

• Demyelinating disease (multiple sclerosis or clinically isolated syndrome) - particularly in younger patients 4
• Pontine hemorrhage (rare) 3
• Pontine tumor (rare) 3

When demyelinating disease is suspected (younger age, subacute onset, T2 hyperintensity without restricted diffusion), obtain CSF analysis and consider MRI of the entire neuraxis to evaluate for additional demyelinating lesions. 4

Treatment

For Ischemic Stroke Etiology

Initiate dual antiplatelet therapy (aspirin plus clopidogrel), high-dose statin, and aggressive vascular risk factor management immediately. 2

Specific management includes:

• Dual antiplatelet therapy for 21-90 days, then transition to single agent 2
• High-intensity statin therapy (atorvastatin 80 mg or rosuvastatin 40 mg daily) 2
• Blood pressure control targeting <140/90 mmHg after acute phase 2
• Glycemic control if diabetic 1, 2
• Supportive care including eye lubrication for facial palsy 2

For Demyelinating Etiology

Administer intravenous methylprednisolone 1 gram daily for 3-5 days when demyelinating disease is confirmed or strongly suspected. 4

The patient in the demyelinating case showed significant improvement with IV steroids, representing the first documented adult case of eight-and-a-half syndrome secondary to demyelination responding to corticosteroids. 4

Prognosis and Recovery

Most patients show gradual improvement over weeks to months with appropriate treatment, with potential for complete resolution of ophthalmoplegia. 1

Expected recovery timeline:

• Ophthalmoplegia: Complete resolution possible by 3 months 1
• Facial nerve palsy: May have minimal residual weakness even after recovery 1
• Overall functional recovery: Good when timely treatment is administered 1

Monitoring During Recovery

• Serial neurological examinations every 2-4 weeks during first 3 months 1
• Repeat MRI at 3 months if demyelinating etiology to assess for new lesions 4
• Ophthalmology follow-up for persistent diplopia or eye movement abnormalities 1

Critical Clinical Pearls

Do not dismiss sudden-onset diplopia with facial weakness as a benign condition - this combination warrants urgent neuroimaging to identify potentially life-threatening brainstem pathology. 2

The presence of preserved vertical eye movements distinguishes eight-and-a-half syndrome from more extensive brainstem lesions that may require different management approaches. 3

In patients with extended pontine infarction involving the corticospinal tract and medial lemniscus, contralateral hemiparesis and hemihypesthesia may occur - this has been termed "nine syndrome" and indicates more extensive pontine involvement. 5