Incidence of progressive multifocal leukoencephalopathy in patients without HIV

To estimate the incidence rate (IR) of progressive multifocal leukoencephalopathy (PML) in patients without HIV.

Within a large US health insurer database between January 2000 and June 2008, we conducted a retrospective observational study. We identified people with autoimmune diseases, chronic lymphocytic leukemia (CLL), non-Hodgkin lymphoma (NHL), or history of bone marrow or solid organ transplantation, and a general population cohort. We developed a PML case-finding algorithm and validated PML diagnoses in medical charts.

There were 138,469 patients with autoimmune diseases, 25,706 with NHL or CLL, and 8,778 with transplants. Among 699 people who met screening criteria for potential PML, 89 had a claim diagnosis of PML (International Classification of Diseases-9 046.3). Medical records were sought for 24 patients without HIV, and 6 had confirmed PML upon review of medical records. The PML IR was 2.4 (95% confidence interval [CI] 0.06-13.18) in the systemic lupus erythematosus cohort and 10.8 (95% CI 0.27-60.39) in the autoimmune vasculitis cohort per 100,000 person-years. In the NHL and CLL cohorts, the IR was 8.3 (95% CI 1.71-24.24) and 11.1 (0.28-61.74) per 100,000 person-years. The IR among patients with bone marrow transplantation was 35.4 per 100,000 person-years (95% CI 0.90-197.29). There were no cases of PML among patients with rheumatoid arthritis (95% CI 0.0-2.24), multiple sclerosis (95% CI 0.0-5.24), Sjögren disease (95% CI 0.0-21.84), or solid organ transplantation (95% CI 0.0-26.81).

In this large population-based investigation of PML with thorough case finding and a known source population, the IR of medical record-confirmed PML was rare in non-HIV patient cohorts.