Pityriasis Rosea
Pronunciation: pit-ih-RY-uh-sis ROH-zee-uh
A self-limiting inflammatory skin eruption characterised by a solitary herald patch followed by a secondary eruption of smaller scaly oval plaques in a Christmas-tree distribution on the trunk.
Full Definition
Pityriasis rosea is believed to be associated with reactivation of human herpesvirus 6 or 7, though it is not definitively classified as infectious. The hallmark 'herald patch' precedes the generalised eruption by one to two weeks and is typically larger than the subsequent lesions. The distribution of secondary lesions along the lines of skin cleavage (Langer's lines) produces the characteristic Christmas-tree pattern on the back. Editors should note that 'pityriasis' (from Greek for bran-like scaling) prefixes several unrelated dermatological conditions and should not be used interchangeably across them.
Usage
Usage note: Do not italicise. 'Pityriasis' appears in multiple diagnostic terms (e.g., pityriasis lichenoides, pityriasis versicolor); these are distinct conditions. Never abbreviate without prior definition.
In Context
- "The herald patch had been present for ten days before the generalised eruption consistent with pityriasis rosea developed." — GP referral letter
- "Secondary syphilis was excluded serologically before a diagnosis of pityriasis rosea was confirmed." — Dermatology consultation note