Treatment for MS-Related Gait Instability on Primidone
Add fampridine (dalfampridine) 10 mg twice daily to improve walking ability in this patient with suspected MS experiencing increased gait instability. Fampridine is the only FDA-approved pharmacological treatment specifically indicated for improvement of walking ability in adults with MS and should be trialed for 2-4 weeks to assess response 1, 2.
Why Fampridine for MS Gait Dysfunction
Fampridine is a potassium channel blocker that improves nerve conduction in demyelinated axons, leading to measurable walking benefits. The evidence demonstrates:
- Significant improvements in walking speed (Timed 25-Foot Walk) and endurance (6-Minute Walk Test) in responders 1, 3
- Response rate of approximately 39% across pooled studies, meaning not all patients benefit 4
- Improved knee flexion during swing phase and reduced mechanical external work, addressing the biomechanical gait abnormalities causing "wobbling and bouncing" 1
Predicting Response
Your patient is more likely to respond if she has:
- Greater baseline walking impairment - severity of walking disability positively correlates with drug response 5
- Younger age - older age reduces probability of response 6
- Lower EDSS scores (if MS confirmed) - higher disability scores reduce response likelihood 6
- Female sex may be less favorable - male sex associated with 2.4x higher odds of response 6
The strongest predictor is poor baseline walking endurance: patients walking <211 meters in 6 minutes show the best response 5.
Dosing and Response Assessment
- Start fampridine 10 mg orally twice daily (morning and evening, approximately 12 hours apart)
- Assess response at 2-4 weeks using objective measures:
- Timed 25-Foot Walk (≥20% improvement indicates response)
- Patient-reported walking ability (12-item MS Walking Scale, ≥6-point reduction indicates response) 6
- Discontinue if no benefit after 2-4 weeks - approximately 33% discontinue due to lack of perceived benefit 6
Safety Considerations
Fampridine is generally well-tolerated with common side effects including:
- Urinary tract infections
- Insomnia
- Dizziness
- Headache
- Nausea
Critical contraindication: History of seizures - fampridine lowers seizure threshold. However, seizure incidence in real-world use is <1% 2.
Why Not Adjust Primidone
Primidone is indicated for seizure disorders, not MS-related gait dysfunction 7. While primidone has anticonvulsant properties through its metabolites (phenobarbital and PEMA), there is no evidence supporting its use for MS gait impairment. The "wobbling and bouncing" described suggests cerebellar ataxia or spasticity-related gait dysfunction from MS pathology, not tremor that primidone might address.
If primidone was prescribed for essential tremor that may be contributing to gait instability, continue it while adding fampridine - they have different mechanisms and indications.
Additional Gait Management Considerations
While fampridine addresses the pharmacological aspect:
- Physical therapy with gait training should be implemented concurrently - evidence supports task-oriented balance training and structured exercise programs for MS gait dysfunction 8
- Assess for spasticity - if present, consider oral baclofen or tizanidine as adjunctive therapy 9
- Rule out other contributors - urinary tract infection, fatigue, heat sensitivity, or MS relapse may worsen gait acutely
Long-term Monitoring
For patients who respond to fampridine:
- Sustained benefit over 12 months is well-documented in real-world studies 2
- Clinical Global Impression scores show 61% of patients maintaining improvement at 12 months versus 11% who discontinued 2
- Re-assess periodically - if walking declines despite fampridine, this may indicate MS progression requiring disease-modifying therapy adjustment 5