The national incidence of PML in Sweden, 1988-2013

Abstract

Objective: To investigate the incidence of progressive multifocal leukoencephalopathy (PML) and patient characteristics in Sweden between 1988 and 2013.

Methods: All PML diagnoses in Sweden between 1988 and 2013 were identified in the National Patient Register. Information to validate the diagnosis and patient characteristics was obtained from medical records.

Results: Medical record review classified 108 out of 250 patients (43%) as definite (n = 84), probable (n = 4), or possible (n = 20) PML according to diagnostic criteria. Accurate diagnoses were more common in records obtained from neurology departments (82% of patients seen in neurology departments) compared with other departments (31%) (p < 0.001). The incidence of PML increased from a largely stable level at 0.026 (95% confidence interval [CI] 0.021-0.031) per 100,000 individuals per year during 1988-2010 to 0.11 (95% CI 083-0.137) during 2011-2013, during which time there was a notable increase (p < 0.001). Hematologic malignancies (n = 34), HIV/AIDS (n = 33), and autoimmune disease (n = 23) were the most common underlying diseases. Treatment with a monoclonal antibody prior to PML diagnosis was identified in 26 patients.

Conclusion: An increased incidence of PML in Sweden was observed and coincided with the prior use of monoclonal antibody treatment. The high level of misdiagnosis emphasizes the importance of immediate contact with a neurology center upon suspicion of PML.

Figure 1. Proportion of correct progressive multifocal leukoencephalopathy (PML) diagnoses over time

Figure 2. Incidence rate of progressive multifocal leukoencephalopathy (PML) in Sweden from 1988 to 2013

(A) The incidence rate of PML per 100,000 person-years in Sweden between 1988 and 2013: each point represents the annual rate; the trend line has 95% confidence intervals (CIs). The incidence rate between 1988 and 2010 was estimated as 0.026 (95% CI 0.021–0.031) and 0.11 (0.083–0.137) between 2011 and 2013. (B) The annual distribution of the 3 most common disease categories associated with PML: HIV/AIDS, autoimmune disease, and hematologic malignancy. Only patients with definite/probable/possible PML are included.