Seasonal variations in dermatologic and dermatopathologic diagnoses: a retrospective 15-year analysis of dermatopathologic data.

Background: Certain dermatologic conditions are known to show seasonal variations in frequency, the reasons for which are unclear but in some cases may be attributable to changes in ambient weather conditions.

Objectives: The current study was conducted to determine whether seasonal trends might exist for dermatologic conditions including erythema multiforme, guttate psoriasis, erythema dyschromicum perstans (ashy dermatosis), pityriasis lichenoides, and pityriasis rosea.

Methods: Data were derived from a 15-year retrospective review of electronic records from a large dermatopathology laboratory located in the mid-Atlantic region of the USA. Numbers of diagnoses per month and "per season" were determined. Pairwise comparisons of seasonal data were made using two-sample t-tests with significance set at P ≤ 0.05.

Results: Perniosis (chilblains) was significantly more common in winter and spring (P = 0.001). Hand, foot, and mouth disease was statistically more prevalent in summer and autumn (P = 0.028). Erythema multiforme was most common in spring and summer (P = 0.004). Grover's disease was most common in winter and spring (P = 0.000039). Guttate psoriasis was non-significantly more common in winter and spring (P = 0.076). No statistically significant seasonal variation was found for erythema dyschromicum perstans (P = 0.899), pityriasis rosea (P = 0.727), or pityriasis lichenoides (P = 0.366).

Conclusions: This study found statistically significant seasonal trends for several dermatologic conditions. The study was primarily epidemiologic and was not intended to address histopathologic differences that might underlie the seasonal variations observed. However, further investigation of seasonal differences in the histopathology of erythema multiforme may prove interesting.