The largest record linkage study to examine an association between the diseases could open inquiry into a protective effect greater than any factor yet observed for development of MS.
HIV and multiples sclerosis (MS) are well known as separate pathological entities, however the relationship between these two diseases remains under-studied. A Danish study in 2013 analyzed the incidence of MS in a newly diagnosed HIV population in the Danish National Registry of Patients and found that among 5018 first presenting HIV patients and more than 50â 000 controls matched for age and sex, the incidence rate ratio (IRR) for an HIV patient acquiring MS was 0.3 (95% CI 0.04 to 2.20). Although this observation did not reach statistical significance it suggested a potential link between HIV infection and a lower risk of MS.1
A recent study published in theJournal of Neurology, Neurosurgery, and Psychiatry re-examines this relationship with provocative results.2 The authors analyzed a national linked data set of English Hospital Episode Statistics to identify all people with HIV who were discharged from National Health Service hospitals, between 1999 and 2011. The investigators also selected a comparison group of individuals without HIV.2
The study included 21â 207 in the HIV cohort and approximately 5â 000 000 in the reference cohort. The median follow-up period for the HIV cohort was 2454â days (IQR 1790â days) and 2756â days (IQR 1951â days) for the reference cohort. The study found that relative risk (RR) of MS in people with HIV, relative to those without HIV, was 0.38 (95% CI 0.15 to 0.79), with 7 observed and 18.3 expected cases.2
When only the people whose first known record of MS was more than a year after the first record of HIV were included, the RR was 0.25 (95% CI 0.07 to 0.65), based on 4 observed and 15.8 expected cases. Restricting the outcome to include only the people whose first record of MS was more than 5â years after the first record of HIV, the RR was 0.15 (95% CI<0.01 to 0.83), based on 1 observed and 6.7 expected cases.2
The authors speculate that the reduced risk of MS in patients with HIV may be related to the immune dysfunction in HIV-infected patients.2 Another possibility could be that antiretroviral therapy interferes with the development of MS.
While this is the largest record linkage study investigating a possible association between HIV and MS, it has methodologic limitations, one being the absence of data on the proportion of the exposed population who were actually taking combination antiretroviral therapy (cART) and the specific combination of drugs they may have been taking during the observation period. The authors note, however, that based on standard of care during the period of data collection, the majority were most likely being treated at the time of study entry or that treatment was initiated if HIV was confirmed at the time of the first admission.
Nonetheless the study does confirm the results of the large Danish study and opens the door to future investigations. The authors write that further confirmatory evidence of a protective effect of HIV and/or its treatment would reveal “the largest protective effect of any factor yet observed in relation to the development of MS.”