First Estimates of Incidence of Progressive Multifocal Leukoencephalopathy Developing Among 10,459 Non-HIV Lymphoma VA Patients Who Receive Rituximab: Results From the Veterans Administration Database (1999–2012).

Progressive multifocal leukoencephalopathy (PML) is a rare but fatal disease that is the result of activation of a highly prevalent dormant JC virus during immunosuppressed states such as advanced HIV, malignancy or immune-modulating medications. Rituximab, an immunomodulator, has been approved for both Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL). We previously reported 57-non-HIV patients developed PML after rituximab (1). This report identified the need for epidemiological cohort studies to further evaluate incidence rates and risk factors for PML by comparing Rituximab treated patients with suitable non-treated patients. Of note, natilzumab-associated PML is now well-characterized, with a reported incidence of 21 PML cases per 10,000 natilizumab-treated persons (2).

In this first such epidemiological study we identified from the national data of the Department of Veteran's Affairs (VA), 61,132 patients with a primary International Classification of Diseases version 9 (ICD-9) code for either HL or NHL between 1999 to 2011 and reported the use of Rituximab among patients with and without PML. This project was conducted inside the Veterans Affairs Informatics and Computing Infrastructure (VINCI) after obtaining approvals from the VA Institutional Review Board and other oversight groups.

We identified 62,642 with a primary diagnosis of HL or NHL and excluded 1,510 (2.4%) patients with VA lab confirmed HIV. Our final cohort had 61,132 patients, 10,459 (17.1%) received Rituximab. A total of 12 (0.020%) patients had developed PML, 5 (0.008%) belonged to the Rituximab group and 7 (0.011%) to non-rituximab group; which results in a statistically significant unadjusted relative risk of 3.46 (95% confidence interval 1.1, 10.9).

Univariate analyses of outcomes other than rate-estimates are not statistically significant between PML patients who received rituximab and those that did not receive rituximab, primarily due to extremely small sample sizes (5 and 7 patients, respectively) (Table 1). Overall, compared to non-rituximab PML patients, rituximab PML patients were younger at PML diagnosis and age of death by more than 6-years; although they did appear to live slightly longer post PML diagnosis by about 4-months.

These results show that among lymphoma patients, the use of Rituximab is associated with a statistically significant relative risk for documented PML of 3.46. We now report a baseline rate among Veterans of 4.78 PML cases per 10,000 rituximab treated Veterans with lymphoma (25% of the rate reported among natilizumab-treated multiple sclerosis patients). As with hepatitis B, measurement of JC virus might be considered prior to initiation of rituximab therapy.

This project was supported through the resources of the Wiliam JB Dorn Veterans Affairs Medical Center.

Disclaimer: The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of the Department of Veterans Affairs or the United States government.

No relevant conflicts of interest to declare.