HealthDay News — Seasonal relapse onset in multiple sclerosis occurs in both hemispheres but varies by latitude, according to data from a study published in the December issue of the Annals of Neurology.

Tim Spelman, MBBS, from Royal Melbourne Hospital in Australia, and colleagues analyzed seasonal relapse onset distribution by hemisphere and latitude location using data from the international MSBase Registry. Data were included from 32,762 relapses in 9,811 patients across 30 countries.

The researchers found that in both hemispheres, relapse onset followed an annual cyclical sinusoidal pattern, with peaks and troughs in early spring and autumn, respectively. There was a mean decrease in ultraviolet radiation (UVR) trough to subsequent relapse peak lag of 28.5 days for every 10 degrees of latitude away from the equator.

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“We demonstrate for the first time that there is a latitude-dependent relationship between seasonal UVR trough and relapse onset probability peak independent of location-specific UVR levels, with more distal latitude associated with shorter gaps,” the authors write. “We confirm prior meta-analyses showing a strong seasonal relapse onset probability variation in the northern hemisphere, and extend this observation to the southern hemisphere.”

Several authors disclosed financial ties to the pharmaceutical and biotechnology industries; the MSBase Foundation receives support from pharmaceutical and biotechnology companies.


  1. Spelman T et al. Ann Neuro. 2014; doi:10.1002/ana.24287.