MS relapses peak in spring, summer as temperatures rise: Study

Relapses in people with relapsing-remitting multiple sclerosis (MS) may be more common in spring and summer, coinciding with warmer temperatures, low humidity, and greater fluctuations in atmospheric pressure, according to a study from Poland.

Stressful life events and infections were the most frequent potential relapse triggers, the study found.

“Better recognition of these issues within future investigations could be considered in the complex approach to the management of MS,” researchers wrote.

The study, “Characteristics of Disease Relapses and Their Relationships with Weather Conditions in Patients with Multiple Sclerosis,” was based on data from a single hospital in Poland and was published in the Journal of Clinical Medicine.

In MS, the body’s immune system mistakenly attacks the brain and spinal cord. In most patients, the disease manifests as periods of worsening symptoms, known as relapses, followed by periods of remission where symptoms ease.

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Searching for patterns

Exactly what triggers an MS relapse is unclear, but a combination of lifestyle and environmental factors, including changes in weather, is thought to play a role.

To know more about the characteristics of relapses in MS patients and whether they followed any pattern over the years, the researchers examined the dates of documented relapses from 80 people with relapsing-remitting MS. They combined that data with climate data for the days preceding the onset of relapse symptoms.

“We focused on the characteristics of MS relapses and their circumstances, in search of patterns which would improve our understanding of their background and potential targets for therapeutic approaches,” the researchers wrote.

On average, patients had been diagnosed for 10 years. Most (92%) were on disease-modifying medications.

From 2015 to 2020, most relapses occurred in March, June, July, and October. When grouped by season, spring and summer showed the highest number of relapses. From 2021 to 2023, relapses increased in May and February, and again were most common in spring, with autumn showing the fewest cases.

“Taking into account the division of months into warm and cold seasons, there was a clear dominance of relapse occurrence in warm months in both analyzed periods,” the researchers wrote.

In 15 patients, relapse was the first manifestation of MS, with patients diagnosed with clinically isolated syndrome. Sensory symptoms — including changes in sensation, tingling, or numbness — were reported only in women and occurred most frequently in January. Optic neuritis, an inflammation of the optic nerve that causes blurred or painful vision, peaked in March.

Motor symptoms with so-called pyramidal signs, such as muscle weakness, were most common in May and June. Cerebellar symptoms, such as balance or coordination problems, increased in March and July. Signs of spinal cord involvement, such as weakness or bladder problems, were more frequent in August.

Nearly two-thirds of patients (62%) reported at least one possible trigger for their relapse. The most common triggers were stressful life events and respiratory infections. A few relapses occurred after vaccination, during pregnancy or the postpartum period, or after surgery.

The weather at the start of a relapse often differed from the monthly average. Temperatures were usually higher, humidity lower, and rainfall less likely. The degree of insolation, a measure of solar energy, was also likely to be greater than average for that month, and fluctuations in atmospheric pressure tended to be greater than normal.

“Observation of seasonal occurrence of relapses and associated weather conditions revealed summer/spring months, in particular periods with high temperature, low humidity, and variable atmospheric pressure as potential contributors,” the researchers concluded, opening ways for future investigations.