Herald Patch as the Only Evidence of Pityriasis Rosea: Clinical, Laboratory and Pathogenetic Features.

Pityriasis rosea (PR) is a self-limited exanthem associated with the endogenous systemic reactivation of human herpesvirus (HHV)-6 and HHV-7. The disease typically begins with a single erythematous patch on the trunk (herald patch), followed by a secondary eruption of smaller papulosquamous lesions. Rarely, the herald patch may be the only cutaneous manifestation of PR. The present work aimed to examine the clinical and laboratory features of the PR cases characterized by the herald patch as the sole cutaneous manifestation and to compare them with the classic form of PR. An observational, retrospective study was conducted on patients presenting with herald patch as the only sign of PR (cases) and on a series of age- and sex-matched patients who presented with a typical PR pattern (controls). The records of the patients were extracted from a PR registry, which collected data on patients with PR diagnosed from 2003 to 2023 by at least two dermatologists from the same study team. Nineteen patients (eleven males, eight females) with a mean age of 27.1 years presented the herald patch as the only cutaneous manifestation of PR. Nineteen age- and sex-matched patients were considered controls. In the cases, the exanthem duration was shorter than in controls, and the mean HHV-6 and HHV-7 DNA plasma load was lower than in controls. This rare variant of PR might be considered an abortive form of the exanthem that occurs when the HHV-6/7 reactivation from latency is contrasted by a more robust immunological response than in classic PR.