From the Guidelines
The workup of internuclear ophthalmoplegia (INO) should focus on identifying the underlying cause, with MRI brain being the cornerstone of evaluation, as it can help detect lesions in the medial longitudinal fasciculus (MLF) and guide further management 1. To evaluate INO, begin with a thorough neurological examination to confirm the classic findings: impaired adduction of the affected eye on lateral gaze with nystagmus in the abducting eye. Key aspects of the examination include:
- Complete ophthalmic examination with emphasis on the sensorimotor evaluation
- Checking for other neuro-ophthalmic signs and symptoms, such as Horner’s syndrome, cranial nerve palsy, and nystagmus
- Fundus examination to check for papilledema or optic atrophy
- Visual field testing to provide additional information on the etiology Order an MRI brain with contrast, focusing on the brainstem, particularly the MLF, as this is the pathway affected in INO 1. Include diffusion-weighted imaging to detect acute ischemic changes. Additional testing should include:
- Complete blood count
- Comprehensive metabolic panel
- Erythrocyte sedimentation rate
- C-reactive protein
- Vitamin B12 levels If multiple sclerosis is suspected, consider cerebrospinal fluid analysis for oligoclonal bands and IgG index, as well as visual evoked potentials 1. For patients with vascular risk factors, carotid ultrasound and echocardiography may be appropriate to evaluate for embolic sources. Depending on clinical suspicion, additional tests may include infectious disease workup (HIV, syphilis, Lyme disease), inflammatory markers, and paraneoplastic antibodies. The comprehensive approach is necessary because INO results from damage to the MLF, which can occur due to demyelination (most commonly multiple sclerosis in young adults), stroke (more common in older adults), trauma, infection, or rarely, tumors 1. Prompt diagnosis of the underlying cause is essential for appropriate management and prevention of further neurological damage.
From the Research
Clinical Presentation of Internuclear Ophthalmoplegia
- Internuclear ophthalmoplegia (INO) is characterized by impaired adduction on the side of a lesion involving the medial longitudinal fasciculus (MLF) with dissociated nystagmus of the abducting eye 2
- The most common causes of INO are vascular (36.9%), multiple sclerosis (32.3%), and infectious diseases (13.8%) 3
- INO can be unilateral or bilateral, and may be associated with other neurological symptoms depending on the underlying cause
Diagnostic Approach
- Magnetic resonance imaging (MRI) is the preferred diagnostic modality for evaluating INO, as it can demonstrate lesions in the MLF 4, 5, 2
- MRI can show focal or nodular areas of high signal intensity on T2-weighted images in the region of the MLF 2
- Infrared oculography can be used to quantify prosaccades and diagnose INO in multiple sclerosis (MS) patients 6
- The versional dysconjugacy index (VDI) can be calculated to describe the ratio between the abducting and adducting eye, and can be used to diagnose INO 6
Lesion Localization
- Lesions affecting the MLF can be localized to different areas of the brainstem, including the ponto-medullary junction, mid pons, upper pons, and mesencephalon 5
- MS patients tend to have multiple lesions in different locations, while stroke patients tend to have lesions at the level of the mesencephalon 5
- The location and extent of the lesion can affect the clinical presentation and prognosis of INO