The likelihood of survival at 2 years was not affected by the number of plasma exchange cycles utilized, the number of natalizumab infusions received prior to diagnosis of PML, or the time from the last natalizumab infusion to starting plasma exchange.
Additional analyses focused on functional ability and disability
A secondary analysis addressed the question of whether plasma exchange has a favorable impact on functional ability. This is an important issue because many MS patients who remain alive 2 years after diagnosis of PML are left with marked permanent disability. This analysis was restricted to the 523 MS patients with PML for whom Expanded Disability Status Scale (EDSS) scores were available 6 months or more after PML diagnosis. The key finding here was that, at 2 years, 62% of the plasma exchange group, but only 38% of non–plasma exchange controls, were either dead or had an EDSS score of 7 or greater, which is a degree of disability likely to render a patient unable to live independently.
Of note, the median EDSS score 6 months before diagnosis of PML was 3.5 in both groups. Moreover, the median EDSS score at the time of diagnosis was similar in the two groups as well: 4.0 in those who underwent plasma exchange and 4.5 in those who did not. So the physician decision to employ plasma exchange clearly was not driven by more-severe disability.
In a multivariate analysis, plasma exchange was independently associated with a 168% increased likelihood of death or an EDSS score of 7 or more at 2 years. A sensitivity analysis restricted to patients who fell into that category was supportive of the main analysis: it concluded that such patients were 159% more likely to have received plasma exchange than not.
Dr. McGuigan cited several study limitations, including possible selection bias, inability to assess the potential impact of other disease-modifying therapies utilized after PML diagnosis, the lack of baseline EDSS scores in a fair number of patients, and the necessity to evaluate all-cause mortality rather than death attributable to PML.
He made a plea for neurologists to diligently submit their own cases of natalizumab-associated PML in MS patients to the Biogen pharmacovigilance database, which is totally dependent upon voluntary physician reporting.
“This is the only tool by which we can get this information at present. It’s the best data we’re likely to be able to get,” he observed.
The study was funded by Biogen. Dr. McGuigan reported receiving research grants from and serving as an advisor to that company and several other pharmaceutical companies.
SOURCE: McGuigan C et al. ECTRIMS 2019, .