Therapeutic Efficacy and Safety of Deep Brain Stimulation for Multiple Sclerosis Related-Tremor: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis of 13 studies involving 131 patients indicates that Deep Brain Stimulation provides a significant reduction in tremor severity for individuals with medication-refractory Multiple Sclerosis, although the evidence is limited by small sample sizes and heterogeneity, with manageable risks including a 7% postoperative infection rate.

The Gist

Imagine your brain is a bustling city with a complex network of roads, highways, and traffic lights. In a healthy brain, the traffic flows smoothly. But for people with Multiple Sclerosis (MS), the "roads" (nerve pathways) get damaged by inflammation and scarring. One specific type of damage causes a very frustrating problem: tremors.

Think of a tremor like a traffic jam that never clears. Your hand wants to pick up a cup of coffee, but the signal gets scrambled on the way to your muscles. Instead of a smooth movement, your hand shakes violently, making simple tasks like eating, writing, or buttoning a shirt nearly impossible.

For many years, doctors tried to fix this with medicine (like trying to calm traffic with a loudspeaker), but often it didn't work. So, they turned to Deep Brain Stimulation (DBS).

What is Deep Brain Stimulation?

Think of DBS as installing a high-tech traffic cop directly inside the brain.

1. The Hardware: Surgeons implant thin wires (electrodes) into a specific part of the brain that controls movement (usually a small area called the Ventral Intermediate Nucleus or VIM).
2. The Power Source: A small battery pack (like a pacemaker) is placed under the skin near the collarbone.
3. The Job: This device sends tiny, controlled electrical pulses to the "traffic cop." Instead of letting the signals jam and cause shaking, the electricity smooths out the traffic flow, calming the tremor.

What Did This Study Do?

The authors of this paper acted like detectives gathering clues. They didn't test new patients themselves; instead, they hunted down every single study ever published about using DBS for MS tremors.

• The Search: They looked through millions of research papers (like searching a massive library) and found 13 studies involving 131 patients who had tried this "traffic cop" surgery.
• The Goal: They wanted to answer two big questions:
  1. Does it work? (Efficacy)
  2. Is it safe? (Safety)

The Big Findings

1. Does it work? (The Good News)

Yes, it works remarkably well.
The researchers combined all the data and found that for most patients, the "traffic jam" cleared up significantly.

• The Analogy: Imagine your hand shaking so hard you can't hold a spoon. After the surgery, for many patients, that shaking reduced by a huge amount (about 1.4 times the standard improvement).
• The Result: People could finally eat, write, and care for themselves again. It wasn't a "cure" for MS, but it was a miracle for the shaking.

2. Is it safe? (The Cautionary Tale)

Like any major surgery, there are risks. The study found that while most people did well, there were some bumps in the road:

• Infections: About 7 out of 100 people got an infection at the site where the battery or wires were put in. This is like a wound getting infected after a car repair; it usually needs antibiotics or, in rare cases, removing the device to fix it.
• Side Effects: Sometimes, the "traffic cop" gets a little too enthusiastic. The electrical pulses might accidentally hit a nearby road, causing temporary side effects like:
  • Slurred speech (dysarthria).
  • Feeling off-balance (disequilibrium).
  • The Good News: These side effects are usually like a software glitch. Doctors can simply "reprogram" the traffic cop (adjust the settings on the battery) to stop the side effects without removing the device.

The Catch (Limitations)

The authors were very honest about the flaws in the evidence, like a careful mechanic admitting, "We have good data, but our sample size is small."

• Small Groups: The studies they looked at were small. Some had only 3 or 4 patients. It's like judging a new car model based on a test drive with only a few drivers.
• Different Recipes: Every surgeon used slightly different settings, targets, or follow-up times. It's like 13 different chefs making the same soup; some used more salt, some used less. This makes it hard to say exactly which recipe is perfect.
• The "Ataxia" Problem: DBS is great at stopping the shaking, but it doesn't fix the weakness or clumsiness (ataxia) that comes with MS. If a patient's legs are weak or they are unsteady, DBS won't magically make them walk straight. It only fixes the shaking.

The Bottom Line

This paper tells us that Deep Brain Stimulation is a powerful tool for people with MS who have severe, uncontrollable shaking that medicine can't fix.

• Think of it this way: If your hand is a shaking camera that can't take a photo, DBS is the tripod that steadies it.
• The Verdict: It's not a perfect solution for everyone, and it requires a skilled surgeon and careful tuning. But for the right patient, it can turn a life of frustration back into a life of independence.

The authors conclude that while the current evidence is promising, we need more large, well-organized studies to figure out the perfect way to use this technology for everyone.

Technical Summary

1. Problem Statement

Multiple Sclerosis (MS) is a chronic neurodegenerative and inflammatory disease affecting the central nervous system. Among its disabling symptoms, tremor (specifically intention and postural tremor) is particularly debilitating, severely impacting activities of daily living (eating, writing, personal care) and quality of life.

• Current Limitations: Pharmacological treatments (anticonvulsants, benzodiazepines) often yield limited benefits, leaving many patients with medication-refractory tremor.
• Surgical Context: While DBS has been established for Parkinson's disease and Essential Tremor, its application in MS remains controversial. Previous evidence is fragmented, characterized by small sample sizes, heterogeneous study designs, variable surgical targets (e.g., VIM vs. ZI), and inconsistent reporting of safety outcomes. There is a lack of a comprehensive, updated synthesis of efficacy and safety specifically for the MS population.

2. Methodology

The study adhered to the PRISMA 2020 guidelines and was registered with PROSPERO (CRD420261347426).

• Search Strategy: A comprehensive search was conducted across PubMed, Scopus, Web of Science, and Embase from inception to December 2025. No language or date restrictions were applied.
• Eligibility Criteria (PICO):
  • Population: Patients with confirmed MS and disabling tremor.
  • Intervention: Deep Brain Stimulation (any target).
  • Comparator: Pre-operative baseline or alternative treatments (e.g., thalamotomy).
  • Outcomes: Primary: Tremor severity reduction; Secondary: Adverse events (infections, hardware complications).
  • Exclusions: Case reports, animal studies, reviews, and studies without extractable tremor data.
• Data Extraction & Synthesis:
  • Included Studies: 13 studies (131 patients) met eligibility; 8 studies (with adequate quantitative data) were included in the efficacy meta-analysis.
  • Statistical Model: A random-effects meta-analysis using the Restricted Maximum Likelihood (REML) estimator with Hartung-Knapp (HK) adjustment was employed to account for anticipated clinical heterogeneity.
  • Effect Size: The primary metric was the Standardized Mean Change (SMC) between baseline and follow-up tremor severity.
  • Data Handling: Studies reporting data as medians/ranges or standard errors were converted to means/SDs using established statistical methods (e.g., Hozo et al. formula).
  • Bias Assessment: Methodological quality was evaluated using the Joanna Briggs Institute (JBI) critical appraisal tools.

3. Key Contributions

• Updated Evidence Synthesis: This is the most recent meta-analysis (searching up to 2025) specifically focusing on MS-related tremor, incorporating large retrospective cohorts (e.g., Chagot et al., 2023) alongside smaller trials.
• Rigorous Statistical Approach: The use of the Hartung-Knapp adjustment provides more conservative and reliable confidence intervals, addressing the limitations of small sample sizes and the low number of included studies.
• Dual Focus on Efficacy and Safety: Unlike previous reviews that often prioritized efficacy, this study systematically pooled safety data, specifically quantifying infection rates and device-related complications.
• Subgroup Analysis: The study investigated whether the method of data extraction (direct vs. converted) influenced the pooled effect size, finding no significant difference, thereby validating the inclusion of studies with varied reporting formats.

4. Results

A. Efficacy (Tremor Reduction)

• Pooled Effect: DBS resulted in a significant reduction in tremor severity.
  • Standardized Mean Change (SMC): 1.42 (95% CI: 1.07 to 1.77).
  • Heterogeneity: Statistical heterogeneity was minimal (I² = 0.0%, p = 0.63), though the authors caution this may be due to the limited number of studies rather than true uniformity.
• Individual Study Range: Effect sizes ranged from 1.26 to 2.51, consistently favoring improvement.
• Subgroup Findings: No significant difference was found between studies using direct data extraction versus those requiring statistical conversion (p = 0.4166).

B. Safety and Adverse Events

• Postoperative Infection: The pooled infection rate was approximately 7% (95% CI: 0.00–1.00), with substantial heterogeneity (I² = 74.1%). Rates varied significantly between studies (e.g., ~2% in large cohorts vs. ~25% in smaller series).
• Surgical Complications: The overall surgical complication rate was estimated at 6–8%, including intracranial hemorrhage and lead malposition.
• Stimulation-Related Side Effects: Transient effects such as dysarthria, disequilibrium, and paresthesia were common but generally reversible with parameter adjustment.
• Device Issues: Long-term complications included lead migration, fracture, and battery exhaustion, necessitating revision surgeries.

C. Quality of Evidence

• Risk of Bias: Overall methodological quality was moderate. Two studies were rated as high risk (Banks et al., Hassan et al.), while one (Hosseini et al.) showed low risk. Common limitations included lack of blinding, small sample sizes, and incomplete reporting of confounders.
• Cognitive/Ataxia Outcomes: The review highlighted that DBS does not improve underlying cerebellar ataxia or cognitive decline, which are common in MS. Patients with severe ataxia often show limited functional improvement despite tremor reduction.

5. Significance and Clinical Implications

• Therapeutic Value: DBS is a viable option for selected patients with severe, medication-refractory MS tremor, offering a large treatment effect (SMC = 1.42).
• Patient Selection is Critical: Success depends heavily on distinguishing tremor from ataxia. Patients with predominant tremor and minimal cerebellar ataxia are the best candidates. DBS does not address the progressive nature of MS or associated ataxia.
• Target Selection: While the Ventral Intermediate Nucleus (VIM) of the thalamus remains the standard target, alternative targets like the Zona Incerta (ZI) and Posterior Subthalamic Area (PSA) show promise and may offer different side-effect profiles (e.g., less dysarthria).
• Future Directions: The authors emphasize the need for larger, prospective, standardized studies with consistent outcome measures and rigorous safety reporting to define the long-term durability of DBS in MS.

Conclusion: Deep Brain Stimulation provides meaningful tremor reduction for a specific subset of MS patients, but the procedure carries a ~7% infection risk and requires careful patient selection to avoid futile interventions in those with severe ataxia. The current evidence base, while promising, is constrained by small sample sizes and methodological heterogeneity.