To evaluate patient’s perception and tolerance of risk for natalizumab-associated progressive multifocal leukoencephalopathy (PML).

PML remains a concern when considering natalizumab for the treatment of multiple sclerosis.   Extensive research has characterized factors that increase PML risk and it is important that both providers and patients understand risk in order to make appropriate risk/benefit decisions.

One hundred U.S. patient-candidates for Natalizumab were questioned about their perception of their PML risk, the maximum PML risk they deemed acceptable, and the sources of information they used to understand risk.  Differences in group distributions were compared using t-test or ANOVA.

Patients estimated their potential PML risk from 0.1% to 87% (mean 31.5%).  Maximum PML risk they deemed acceptable ranged from 0.1% to 45% (mean 14.5%). Men and women perceived their PML risk similarly (28% men, 34% women) but women were willing to accept a higher risk (13% vs. 34%).  Older patients perceived PML risk to be higher, whereas willingness to accept risk remained similar among all ages.  Those with higher levels of education (high school vs. bachelors vs. masters) estimated more accurate (lower) risk (44%, 33%, and 8%, respectively).  The same significant trend was observed for risk tolerance (19%, 15%, and 8%, respectively).  Blacks, Whites, and Hispanics estimated PML risk and risk tolerance at similar levels, while Asians estimated more accurate (significantly lower) risk values (although greater proportion of Asians had higher education level).  Neither risk perception nor tolerance was correlated with disability level (as measured by EDSS scores).

Patients significantly overestimated their PML risk, often by two orders of magnitude.   Most patients in this cohort were willing to accept a PML risk much higher than their actual risk.  This discrepancy between real and perceived risk may represent an important need for patient education.