Incidence of progressive multifocal leukoencephalopathy in patients without HIV

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

Methods: 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.

Results: 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).

Conclusions: 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.