Pityriasis rosea (PR) will develop suddenly. It is a self-limiting eruption, which means it will subside on its own after specified duration if not treated. It runs a unique and constant course lasting about six weeks.
Prevalence of Disease:
The prevalence of PR in total population has been calculated as 0.12% in men and 0.15% in women, mostly in the age group of 10 to 44 years, even infant cases have been recorded. According to temperate and climate, the incidence is more in winter, though in a few countries it is seen more often in the hot and dry season.
The exact cause is unknown, though the following factors may be relevant:
In classic Pityriasis rosea, the primary eruptions also called as herald patch or mother patch, seen in 50% to 90% of cases on their covered truncal area. It reaches a diameter of a few centimeters within a few days. It is oval or round with a central, wrinkled, salmon-colored area and a darker red peripheral zone separated by a collarette of fine scales. Secondary eruption follows the herald plaque by two days to two months. It appears in crops and reaches its maximum in about 10 days as symmetric eruption covering the trunk, adjacent neck and proximal parts of the extremities lasting for 2 to 10 weeks. However, the eczematous or drug-induced eruptions may take longer to clear.
In the typical secondary rash, eruptions smaller than the primary plaque co-exist. Small plaques resemble the herald patch in miniature, along with the lines of cleavage. On the trunk, it is present with a Christmas tree pattern and on the back in a Chevron pattern. There will be small, red and usually non-scaling papules. Itching is severe in 25% of the cases, slight or moderate in 50% and absent in 25%.
Atypical Pityriasis rosea (20%) variants may either be the primary or secondary rash. Herald patch fails or does not appear at all. Sometimes, two or more herald patches appear. The secondary eruption may not appear at all or be restricted to the extremities, not on trunk (PR inverse) or involve the face, which is not a usual site, especially in the children. It may be vesicular, pustular, urticaria-like or purpuric, mainly in children. It is rarely localized or unilateral. Sometimes, there will be large lesions, confluent in a circinate pattern (rolled up leaves as in fern).
Course and Prognosis:
Usually self-limiting, lesions fade after 3 to 6 weeks, sometimes leave residual hypo and hyperpigmentation, which is entirely reversible. Recurrences are unusual and may occur in 2% of the cases. Black races are more prone to recurrent pityriasis rosea.
The blood picture is usually standard, but leukocytes count can be raised, raised neutrophil and eosinophil may occur occasionally.
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