Ocular movement disorder caused by lesion of medial longitudinal fasciculus (MLF), characterized by impaired adduction of the ipsilateral eye with nystagmus of the abducting eye.
Aetiology
Brainstem infarctions (⅓ cases):
Usually unilateral and seen in older individuals
Demyelinating disorders (⅓ cases):
Mostly bilateral and seen in young adults and adolescents.
- Multiple sclerosis (MS) (23% cases)
Other causes:
- Trauma
- Tentorial herniation
- Infections (HIV, syphilis, cysticercosis, herpes zoster, tuberculoma)
- Tumours (medulloblastoma, glioma, lymphoma, metastases)
- Vasculitis (systemic lupus erythematosus (SLE), Sjogren syndrome)
- Iatrogenic injury
- Brainstem hemorrhage
Pathophysiology
Brain structures involving the horizontal movement in eyeballs:
- Paramedian pontine reticular formation (PPRF)
- Abducens nucleus
- Medial longitudinal fasciculus (MLF)
Disorders of horizontal movement in eyeballs:
Resulting from the damage to the above brain structures
- Horizontal gaze palsy
- Internuclear ophthalmoplegia (INO)
- One-and-a-half syndrome
Medial longitudinal fasciculus (MLF):
Paired white matter tract passing close to the midline, through the brainstem lying ventral to the cerebral aqueduct in the midbrain and the fourth ventricle in the pons and medulla that serves as the final common pathway for different types of conjugate eye movements like saccades, smooth pursuit, vestibulocochlear reflex, and forms a communication between all the ocular motor nuclei
- Lesion of the medial longitudinal fasciculus can produce impaired horizontal conjugate eye movements by blocking the connection between contralateral sixth nerve nucleus and the ipsilateral third nerve nucleus, thus affecting horizontal gaze
Clinical features
- Total/partial failure of adduction ipsilateral eye
- Monocular nystagmus of abducting eye
Diagnosis
MRI:
Diagnostic imaging of choice for MLF lesions in patients with INO
Management
Treatment of underlying cause