Seasonal variations in activity of systemic lupus erythematosus in a subarctic region

Photosensitivity is one of the major clinical features of Systemic Lupus Er ythematosus (SLE), and is considered to be implicated in the disease pathog enesis. We studied seasonal variations of SLE disease activity at latitude 70 degrees North LI here there is no sunlight in the winter time, in contra st to 24 h daily sunlight in the summer (midnight sun). The associations be tween the level of plasma melatonin in June and December with disease manif estations were also studied. Twenty-one SLE patients were examined each month for 1 y, and disease activ ity was assessed by laboratory parameters as well as clinical disease activ ity parameters SLEDAI and doctor's global assessment. Melatonin levels were quantified by a RIA-assay. There was no significant change of clinical measures or laboratory paramete rs of disease activity from one month to the next during the one year, exce pt photosensitive rashes. January was the only month without SLE-flares or arthritis, in contrast to rest of the year. The levels of plasma melatonin were highest in December for seven patients and highest in June for one pat ient (P < 0.005). Plasma melatonin levels did not correlate with measures o f clinical disease activity. At a latitude of 70 degrees North there were no major seasonal variations i n SLE disease activity during the one year. There was an accumulation of ph otosensitivity in the summer months, but no indications of worsening of the disease in the winter months. In contrast to the rest of the year, there w as no flare in January which had only 5.6 h of sunshine. The level of p-mel atonin did nor correlate with measures of disease activity.