AMSTERDAM – Both air temperature and air pollution levels affected the likelihood of experiencing a flare in systemic lupus erythematosus (SLE) organ-specific disease activity in a study presented at the European Congress of Rheumatology.
For every 1° F increase in temperature, there was an increase in the odds of experiencing a skin flare (odds ratio, 1.0075), joint flare (OR, 1.0110), or neurologic flare (OR, 1.0096), reportedand associates during one of the poster sessions. Conversely, renal flares were less likely to occur with rising temperature (OR, 0.9960). The latter is something previously reported, Dr. Stojan said in an interview, “as we found most renal flares occur in the winter, not in the summer months.”
Furthermore, for every 1 mcg per cubic meter increase in fine particulate matter pollution (PM2.5), there were increases in serositis (OR, 1.0240) and hematologic flares (OR, 1.011).
There were two reasons for looking at the role of these environmental factors in relation to SLE flares, said Dr. Stojan, an assistant professor of medicine at Johns Hopkins University, Baltimore. “The first was a clinical observation – I was getting clusters of patients with certain disease manifestations, for example with serositis or joint flares, and there wasn’t a random distribution.”
The second was a patient observation, added Dr. Stojan, who is also codirector of the Johns Hopkins Lupus Center. Every year, patients treated at the Center have the opportunity to meet each other and hear about the research being done by the team, and it was at this meeting that patients said they felt they were experiencing similar disease flares.
To look at the underlying role of environmental exposures in the development of SLE and possible associations with disease activity, Dr. Stojan and associates used a method known as cluster detection, which is commonly used in public health studies.
The investigators used a 350-km radial zone around the Johns Hopkins Lupus Center for the analysis as this was an area where a uniform number of patients treated by the center were living. They obtained data on 1,261 patients in the Hopkins Lupus Cohort, spanning a 10-year period from 1999 to 2009, and used SaTScan software to identify clusters of disease activity occurring during 3 separate monthly time intervals in different counties. The researchers then linked these clusters to average temperature and PM2.5 data obtained from the Environmental Protection Agency for the 10 days prior to patients’ visits.
“The SaTScan system predicts how many flares per organ system you would expect in a county based on the number of patients and based on the total flares we have in our cohort,” Dr. Stojan explained. Previously, the system helped to identify areas that had a higher flare incidence for each organ system that lasted for about 2-3 years, did not overlap, and could not be explained. So, the next step was to look for potential environmental triggers.
“Basically, the SaTScan adjusts the data that’s inputted for temperature and small particulate pollution. If the cluster moves in space and time then these did affect it,” Dr. Stojan said. “It seems that these do affect certain types of organ flares,” even after adjustment for other variables such as patients’ age, gender, income, ethnicity, and living situation (rural or urban).
Flares in skin symptoms during the summer have been identified before, he acknowledged, but the link to joint flares or neurologic flares have not. The latter includes things like seizures, neuropathy, or abnormal brain imaging rather than mood changes or mild cognitive dysfunction.
These data could have an impact on how clinical trials are designed, Dr. Stojan added, suggesting that factoring in where patients live and how close they are to areas of pollution could ensure a uniform population of patients is studied.
From a more practical perspective, these data might help to develop predictive models to help understand when patients are likely to experience a flare and if any action can be taken to ameliorate the effects of exposure.
The next step is a collaboration with patients to develop software or a mobile application where patients could input information about any disease flares. This would enable a finer view of what could be happening, Dr. Stojan said, as while daily readings are available for the environmental factors studied, disease activity data is only available during 3 separate monthly intervals. It would also allow other environmental factors to be considered.
“I think this is an important step in figuring out environmental factors and their influence on lupus,” he said. “There has been an extensive amount of research into viral causes and potential infectious triggers, but spatial-temporal analysis of environmental variables have never been done before in lupus.”
The study received no commercial funding, and Dr. Stojan reported having no disclosures.