What is the management of internuclear ophthalmoplegia (INO)?

Management of Internuclear Ophthalmoplegia (INO)

Immediate Diagnostic Priorities

The first step in managing INO is determining the underlying etiology through urgent neuroimaging, as the cause dictates both prognosis and treatment approach. 1

Age-Based Differential Diagnosis

• Younger patients (< 50 years): Multiple sclerosis is the primary consideration, particularly with bilateral INO 1
• Older patients (> 50 years): Acute brainstem stroke is the leading cause, especially with unilateral INO 1
• All ages: Consider trauma (20% of unusual cases), tumors (17%), infection (17%), hemorrhage (13%), and iatrogenic injury (12%) 2

Essential Imaging

• MRI of the brain with and without contrast is the preferred modality, including high-resolution T2-weighted images of the brainstem to visualize the medial longitudinal fasciculus (MLF) 1
• MRI may fail to reveal lesions in up to 75% of cases despite clinical INO, particularly in acute ischemic events 3
• If stroke is suspected, refer to cerebrovascular disease protocols for vascular imaging (CTA or MRA) 1

Acute Management Based on Etiology

For Stroke-Related INO

• Manage as posterior circulation stroke with appropriate acute stroke protocols 1
• Most cases recover completely within 1-22 days (average 9.3 days) 3
• Monitor for associated neurologic deficits (hemiparesis, sensory loss, ataxia, Horner's syndrome) 1

For Multiple Sclerosis-Related INO

• Coordinate care with neurology for disease-modifying therapy 1
• Bilateral INO strongly suggests demyelinating disease in younger patients 2

For Tumor-Related INO

• Bilateral INO in the context of known brain tumor indicates significant dorsal pontine invasion and often represents progressive disease 4
• Urgent neurosurgical and neuro-oncology consultation is required 4

Symptomatic Treatment of Diplopia

Initial Conservative Management

• Prism therapy: First-line symptomatic treatment while awaiting possible spontaneous recovery 1
• Occlusion therapy: Alternating eye patching for patients with disabling diplopia (used in 31% of refractory cases) 5
• Monitor for 3-6 months before considering invasive interventions, as many cases improve spontaneously 5, 3

Botulinum Toxin Injection

For persistent, disabling diplopia after 3-6 months, botulinum toxin A injection into extraocular muscles provides symptomatic relief in 87.5% of patients. 5

• Reduces diplopia in 87.5% of cases 5
• Improves appearance in 56.3% and head posture in 25% 5
• May restore convergence (12.5%) and improve stereopsis (18.8%) 5
• Complications: Transient ptosis, overcorrection, or temporary vertical diplopia (resolves within 3 weeks) 5
• Requires maintenance injections in 31.5% of patients for sustained benefit 5

Surgical Intervention

• Reserved for cases unresponsive to conservative measures and botulinum toxin 5
• Strabismus surgery may be considered for stable deviations after 6-12 months 1
• Goals should be customized: reducing diplopia, correcting head tilt, and minimizing perceived visual tilt 1

Associated Symptoms Requiring Attention

Vertigo and Vestibular Symptoms

• INO associated with acute vestibular neuronitis presents with severe vertigo, dizziness, nausea, and vomiting 1
• Coordinate with neurology or otolaryngology for vestibular rehabilitation 1

Skew Deviation

• Often coexists with INO and causes vertical diplopia with subjective visual tilt 1
• Rostral pons/midbrain lesions cause contralateral hypotropia; medullary lesions cause ipsilateral hypotropia 1

Critical Pitfalls to Avoid

• Do not dismiss unusual etiologies: 28% of INO cases have causes other than MS or stroke, including trauma, tumor, and infection 2
• Do not delay neuroimaging: Even with classic clinical findings, imaging is essential to identify treatable causes like tumor or hemorrhage 1, 6
• Do not assume bilateral INO equals MS: While bilateral INO is more common in MS (73% unilateral in MS vs 13% in stroke), tumors and other causes can present bilaterally 2
• Do not overlook progressive disease: In patients with known brain tumors, bilateral INO indicates significant brainstem invasion and poor prognosis (death within 1-9 months) 4

Specialist Referrals

• Neuro-ophthalmology: For complex cases requiring specialized motility assessment 1
• Neurology: For suspected MS, stroke, or other neurologic conditions 1
• Neurosurgery/Neuro-oncology: For tumor-related INO 4
• Orthoptists: Can assist with examination, prism fitting, and non-surgical management under ophthalmologist supervision 1