Medial Longitudinal Fasciculus (MLF) Syndrome
Diagnosis
MLF syndrome presents with impaired adduction of the ipsilateral eye and dissociated nystagmus of the contralateral abducting eye during lateral gaze, with preserved convergence. 1, 2
Clinical Features to Identify
- Diplopia exacerbated during lateral gaze is the primary presenting symptom 3
- Adduction paresis of the affected eye with nystagmus in the abducting eye (internuclear ophthalmoplegia) 1, 2
- Convergence typically remains intact, distinguishing this from other ocular motor disorders 4
- In bilateral MLF syndrome, both eyes show adduction deficits with bilateral abducting nystagmus 4
- Vertical oscillopsia may occur with vertical head movements due to vertical VOR deficits 2
Neuroimaging Protocol
MRI of the brain is the imaging modality of choice, with specific focus on the brainstem. 3
- Use at least 1.5T or 3T scanners for adequate resolution of small MLF lesions 3
- Obtain high-resolution T2-weighted and FLAIR sequences to visualize paramedian midbrain and pontine lesions 3
- 3D T1 post-contrast images with isotropic 1mm voxels help detect small enhancing brainstem lesions 3
- High-b-value diffusion-weighted imaging (DWI) reveals acute ischemic changes more clearly than standard-b-value DWI, particularly for small pontine infarctions 1
Etiologic Workup
Consider infectious, inflammatory, vascular, demyelinating, and traumatic causes. 3, 5
- Multiple sclerosis is a common cause in younger patients with bilateral MLF syndrome 2
- Ischemic stroke is the most common cause overall, particularly in older patients 1, 5
- Inflammatory conditions including sarcoidosis, giant cell arteritis, and granulomatous disease require evaluation 3, 5
- Infectious etiologies such as tuberculosis, fungal infections, or Lyme disease must be excluded 3
- Trauma can cause MLF syndrome through primary injury, herniation, or vascular shearing 6
For suspected inflammatory or infectious causes:
- Perform lumbar puncture with CSF analysis including cell count, protein, glucose, cytology, acid-fast bacilli smear/culture, fungal culture, VDRL, and cryptococcal antigen 7
- Obtain inflammatory markers (ESR, CRP) and consider temporal artery biopsy if giant cell arteritis is suspected 5
- Gadolinium-enhanced MRI showing leptomeningeal enhancement suggests granulomatous disease 7
Treatment
Acute Ischemic Stroke
For acute brainstem ischemia causing MLF syndrome, standard acute stroke protocols apply. 1
- High-b-value DWI confirmation supports thrombolytic therapy decision-making in the appropriate time window 1
- Initiate antiplatelet therapy and vascular risk factor modification for secondary prevention 1
Inflammatory/Infectious Causes
Treatment depends entirely on the underlying etiology identified. 7, 5
For tuberculous meningitis:
- Multi-drug anti-tuberculous therapy (isoniazid, rifampin, pyrazinamide, ethambutol) for minimum 12 months 7
- Adjunctive corticosteroids to reduce inflammation and prevent complications 7
For fungal meningitis:
- Prolonged antifungal therapy based on the specific organism identified 7
For neurosarcoidosis:
- High-dose corticosteroids (prednisone 1 mg/kg/day) as first-line therapy 7
- Steroid-sparing immunosuppressants (methotrexate, azathioprine, mycophenolate) for maintenance 7
For giant cell arteritis:
- Oral prednisolone (1 mg/kg/day) with monitoring of inflammatory markers 5
Multiple Sclerosis
For MS-related MLF syndrome, disease-modifying therapy per MS treatment guidelines is indicated. 2
- Acute exacerbations may warrant high-dose intravenous methylprednisolone 2
Symptomatic Management
If elevated intracranial pressure develops, CSF diversion devices (ventriculoperitoneal shunts) provide palliative relief. 7
Prognosis
Prognosis varies dramatically by etiology. 7
- Post-traumatic MLF syndrome often shows gradual improvement with complete recovery possible within 20 days 6
- Ischemic stroke-related MLF syndrome prognosis depends on infarct size and vascular risk factor control 1
- Infectious causes like tuberculous meningitis carry 20-50% mortality even with treatment 7
- Neurosarcoidosis typically responds well to immunosuppression with good long-term outcomes if diagnosed early 7
- MS-related MLF syndrome may show partial recovery but often leaves residual VOR deficits causing oscillopsia during head movements 2