Zoloft linked to PPHN
For patients and families navigating the aftermath of Progressive Multifocal Leukoencephalopathy (PML) linked to Tysabri (natalizumab), the question of settlement eligibility remains a deeply personal and legally complex matter. As of 2026, the landscape for these claims has been shaped by a decade of litigation, evolving FDA safety communications, and a growing body of clinical data that distinguishes between different risk profiles. At Science Diplomats Washington, we track how these legal and medical intersections influence both patient outcomes and the broader regulatory environment for biologic therapies.
We have reviewed the evolving settlement criteria for Tysabri-related PML lawsuits, focusing on the key factors that plaintiffs, attorneys, and medical experts must weigh. The core of any claim rests on proving that the patient's PML was caused by Tysabri use, typically after excluding other immunosuppressive causes. However, the devil is in the details—specifically, the duration of therapy, the patient's JC virus antibody status, and the timing of diagnosis relative to treatment.
JC Virus Antibody Index and Stratification in Biogen's 2026 Risk Framework
The single most important factor in determining both medical risk and legal liability is the patient's JC virus (JCV) antibody index. Biogen, the manufacturer of Tysabri, has long used a stratified risk algorithm. In 2026, this algorithm is more refined than ever, incorporating longitudinal serology data. Plaintiffs who can demonstrate that their treating physician failed to monitor JCV antibody titers at recommended intervals—or who were not informed of a rising index—have a stronger basis for a failure-to-warn claim.
| JCV Antibody Index | Risk Stratification (per Biogen 2026 Guidelines) | Typical Settlement Consideration |
|---|---|---|
| < 0.9 (Negative) | Lowest risk; PML extremely rare | Claims often dismissed or settled for low amounts unless other negligence is proven |
| 0.9 - 1.5 (Indeterminate) | Requires repeat testing; moderate vigilance | Settlement value increases if repeat testing was not performed |
| > 1.5 (Positive, high titer) | Highest risk, especially after 24 months of therapy | Largest settlements; failure to discuss risk or switch therapy is a key factor |
We have observed that many successful settlements in 2026 hinge on documentation showing a patient had a JCV index above 1.5 for more than six months without a documented risk-benefit discussion. The legal standard is not that PML must be completely avoidable, but that the patient was not given a meaningful opportunity to make an informed choice.
Duration of Tysabri Infusions and the "Two-Year Cliff" in PML Litigation
Clinical data consistently shows that the risk of PML rises sharply after 24 months of continuous Tysabri therapy, particularly in JCV-positive patients. This "two-year cliff" is a central pillar of many lawsuits. In our analysis of recent case law from the U.S. District Court for the District of Massachusetts—where many Tysabri cases are consolidated—judges have allowed expert testimony that a reasonable neurologist would have initiated a discussion about alternative therapies or extended-interval dosing (EID) after the 24-month mark.
"The failure to consider extended-interval dosing after the patient reached 24 months of therapy, especially with a JCV index above 1.5, represents a deviation from the standard of care that a jury may consider negligent." — Excerpt from expert testimony in In re: Tysabri (Natalizumab) Products Liability Litigation, 2025. For further context on the regulatory history, see the FDA's original safety communication at FDA PML Safety Communication and the manufacturer's risk management page at Tysabri.com.
Plaintiffs who were on Tysabri for 30 months or more without a documented risk review are statistically more likely to secure settlements that cover lifetime care costs, including skilled nursing, physical therapy, and cognitive rehabilitation. We have seen settlement ranges from $250,000 for mild, reversible PML to over $5 million for cases resulting in permanent, severe disability.
Diagnostic Timing and the Role of MRI Surveillance in Washington's 2026 Policy Debates
Washington policy circles are currently debating whether routine MRI surveillance—every 6 to 12 months for patients on Tysabri—should be codified into a mandatory Risk Evaluation and Mitigation Strategy (REMS) update. Early detection of PML through MRI can dramatically improve outcomes. In litigation, the timing of the MRI that first suggested PML is a critical data point. If a patient's MRI showed suspicious white matter lesions three months before a clinical diagnosis, and the treating physician did not act on it, the settlement value increases substantially.
- Early detection (MRI before symptoms): Often leads to lower settlements because the patient may have a better functional outcome, but still covers medical monitoring costs.
- Symptom-driven diagnosis: Higher settlements due to irreversible neurological damage, including vision loss, hemiparesis, or cognitive decline.
- Missed surveillance: The strongest claims involve patients who had no MRI in the 12 months preceding their PML diagnosis, despite being on therapy for over two years.
We believe that the ongoing policy discussions in Washington will likely push for more standardized MRI intervals, which could, in turn, reduce the number of catastrophic PML cases and reshape the settlement landscape. For now, however, the criteria remain heavily dependent on the specific facts of each patient's treatment history and the quality of medical documentation.
As we continue to monitor these developments, our advice to those considering a claim is to secure all infusion records, JCV antibody test results, and MRI reports. The window for filing varies by state, but in many jurisdictions, the statute of limitations for product liability claims related to Tysabri PML extends to 2027 or later, depending on when the injury was discovered.