Pityriasis rosea: elucidation of environmental factors in modulated autoagressive etiology and dengue virus infection.

INTRODUCTION: A retrospective epidemiological study was conducted to study seasonal variation in the incidence of pityriasis rosea (PR) and its temporal association with various meteorological variables, and dengue virus infection.

METHODS: The study was conducted at a tertiary referral center in Guwahati, Assam, India. We searched for and retrieved all medical records of patients diagnosed with PR by dermatologists from December 1st, 2014 to July 31st, 2017. The diagnosis was made only if the patient fulfilled at least three out of the following four clinical features: 1) herald patch, 2) peripheral collaret scales, 3) predominant truncal and proximal limb distribution of the lesions, and 4) orientation of lesions along the lines of cleavage. For each visit by every patient, we retrieved data for the monthly mean air temperature, mean total rainfall, and mean relative humidity. PR patients that had dengue fever with NS1 antigen and/or IgM/IgG antibody positivity were studied along with healthy controls.

RESULTS: Overall, PR occurred more frequently in the colder months and months with less rainfall. However, these associations were insignificant (p = 0.23, R = -0.38, and R = -0.55, respectively). Upon further examination of the data, we found that the monthly incidence of PR was significantly lower in March and April than the other months during the study period (F = 8.31, p = 0.002). A statistically significant higher incidence was detected in September, November, and December (p < 0.01 for 2014 and 2017, but not in the 2016 seasonal cohort) and also in January and February (p < 0.05 for 2016 and 2017). Interestingly, a retrospective history of dengue fever emerged as a significant correlate.

CONCLUSIONS: In our setting, there was significant temporal clustering and seasonal variation among patients with PR. The incidence of dengue fever is significantly correlated with PR.