STOCKHOLM – , said at the annual congress of the European Committee for Treatment and Research in Multiple Sclerosis.
This is speculative, he readily acknowledged, but it is a hypothesis supported by multiple lines of evidence provided by separate Swedish national health care registry studies he has led that showed associations between pneumonia or infectious mononucleosis occurring in early adolescence and increased risk of later MS.
These findings are consistent with the well-established observations that two other causes of lung irritation – cigarette smoking and exposure to organic solvents – are also linked to increased risk of MS (), noted Dr. Montgomery, head of the clinical epidemiology research group at Örebro (Sweden) University.
Moreover, he and his coinvestigators also found in yet another Swedish national registry cohort study that one concussion during adolescence was independently associated with a statistically significant 1.22-fold increased risk of later MS, while two or more were linked to a 2.33-fold increased risk. In contrast, concussions occurring before age 11 years were not associated with any increased risk of MS, which suggests an age-defined period of susceptibility ().
“There seems to be greater brain resilience in childhood as compared to adolescence,” Dr. Montgomery commented.
The new Swedish registry pneumonia study included 6,109 Swedish MS patients and 49,479 controls matched for age, gender, and locale. In an analysis adjusted for education level and history of infectious mononucleosis, history of having pneumonia at age 11-15 years was independently associated with a 2.8-fold increased risk of subsequent MS. Pneumonia occurring at age 16-20 years was associated with a more modest 1.38-fold increased risk, which did not achieve statistical significance, while pneumonia up to age 5 years or at age 6-10 years conferred no increased risk. The investigators restricted their analysis to cases of pneumonia occurring up to age 20 years because that is younger than the typical age of MS onset. The age restriction sidestepped the potential for confounding by reverse causation since it is known that pneumonia occurs with increased frequency in patients with MS.
Because MS patients also have an increased risk of urinary tract infections, Dr. Montgomery and coinvestigators also analyzed the same pediatric data set for UTI rates broken down by 5-year age groups. Rates were similar in individuals who later developed MS and in controls, which suggests that the observed increase in MS risk associated with pneumonia in early adolescence was not an expression of an MS prodromal illness, he explained.
The investigators focused on pneumonia in childhood and adolescence as a potential trigger for MS because pneumonia results in more profound and prolonged inflammation than do other common respiratory illnesses. For example, pneumonia has been shown to be linked to increased risks of cardiovascular disease and chronic kidney disease for up to 5 years after the infection.
Developmentally, age 11-15 years is a period defined by peripubertal reorganization and synaptogenesis, while synaptic pruning and axonal myelination are on the agenda at age 16-20 years, Dr. Montgomery observed.
The study of infectious mononucleosis as a potential risk factor for MS included 4,527 Swedish MS patients and 3.2 million controls, all born during 1970-2000 and followed until 2014. In this analysis, infectious mononucleosis occurring at age 11-15 years was associated with the greatest risk of subsequent MS, with an associated 3.47-fold greater risk of the neurologic disease versus that seen in patients who did not have infectious mononucleosis at age 11-15 years
“It does look like a causal association between Epstein-Barr virus infection and subsequent MS,” according to Dr. Montgomery.
He noted that a plausible mechanism by which lung inflammation could predispose future MS has been put forth by German investigators. Using an animal model, they demonstrated that autoreactive T cells are prepared in bronchus-associated lymphoid tissue and attain a migratory profile allowing them to cross the blood-brain barrier and induce CNS autoimmune disease ().
All of this, as Dr. Montgomery emphasized, is speculative at this point in regard to MS pathogenesis. What is not speculative, he continued, is the solid evidence that infection-related mortality after diagnosis of MS has gone down substantially in the current era of newer disease-modifying treatments, as he and his coinvestigators have demonstrated ().
“People with MS, compared to the general population, are still at increased risk, but not nearly as much as the infection-related mortality risk present back in the 1960s-80s. So things have improved somewhat,” Dr. Montgomery said.
Which MS patients are at increased risk for mortality caused by infection? His Swedish national registry research demonstrates that the risk is essentially confined to patients with secondary or primary progressive MS or an Expanded Disability Status Scale score of 6 or more.
Another new study he presented at the meeting focused on the types of infections that are more common in a contemporary MS population than in MS-free individuals. This Swedish national cohort study included 6,602 patients diagnosed with MS during 2008-2016 and 61,828 age-, sex-, and location-matched controls. Infections serious enough to have resulted in hospitalization occurred 2.59 times more frequently in the MS population. The risk of meningitis and encephalitis was increased 6.16-fold, opportunistic infections were 2.72-fold more frequent, the risk of urinary tract and kidney infections was increased 2.44-fold, herpes virus infections were increased 2.32-fold, and the combined rate of pneumonia and influenza was roughly double that seen in the matched general population.
Dr. Montgomery reported receiving research funding from F. Hoffmann–La Roche, Novartis, and AstraZeneca and serving on an advisory board for IQVIA.
SOURCE: Montgomery S. ECTRIMS 2019, .