Can Unilateral Pityriasis Rosea be Considered a Form of Superimposed Lateralized Exanthem?
Francesco Drago1, Giulia Ciccarese2, Aurora Parodi3
1 Professor, Department of Dermatology, IRCSS AOU San Martino IST, Genoa, Italy.
2 PhD Student, Department of Dermatology, University of Genoa, Genoa, Italy.
3 Professor, Department of Dermatology, University of Genoa, Genoa, Italy.
NAME, ADDRESS, E-MAIL ID OF THE CORRESPONDING AUTHOR: Dr. Giulia Ciccarese, 10, Largo Benzi, Genoa-16132, Italy.
E-mail: giuliaciccarese@libero.it
To the Editor,
We read with interest the paper by Badakhsh H et al., about a case of unilateral Pityriasis Rosea (PR) that prompted us to make some considerations and report our experience [1].
Although the authors stated the aetiology of PR is probably viral but still controversial [1]. More recent studies established a causal role for systemically active Human Herpesvirus-6 (HHV-6) and Human Herpesvirus-7 (HHV-7) infection in the pathogenesis of PR, based on the detection of HHV-6 and HHV-7 DNA in plasma, virus mRNA expression and specific viral antigens in skin lesions of PR patients [2]. As for other exanthems, PR may be atypical not only in the morphology or distribution of the lesions, as reported by Badakhsh H et al., [1] but also atypical in the course: persistent (lasting more than 12 weeks) [3] and relapsing [4] PR forms have recently been described in adults whereas in children PR seems to have a shorter duration (14 days) compared to adult patients [4]. Sometimes, the eruption may be confined to a single area of the body or may have an unilateral distribution. There are cases in which PR is limited only to the herald patch localised unilaterally in the axilla. The lesions of Pityriasis Circinata et Marginata of Vidal, sometimes regarded as a special form of PR, are few and large, often localised to only one area of the body (axillae or groins), tend to become confluent and may persist for several months. Generally, the trunk is the most common site in localised PR. Probably, many forms of the so called “unilateral laterothoracic exanthem” or, according to Happle R, “superimposed lateralized exanthem” (SLEx) are actually forms of PR that remains localised to axilla or involves mainly the trunk in an unilateral pattern [5]. In our updated series of 675 PR cases, an atypical presentation of the exanthem starting from the axilla or presenting a strictly asymmetrical involvement was observed in 12 patients (1.8%), nine adults and three children. In ten of them (83%), an endogenous HHV-6 or HHV-7 systemic reactivation was detected through serology and HHV-6/7 plasma viremia.The unilateral presentation of PR may be explained by the increased responsiveness of a polygenic predisposed side of the body to develop an inflammatory eruption directed against various infectious agents. SLEx may exemplify a mosaic disorder following an arrangement along the Blaschko’s lines and several cases of SLEx may simply represent forms of atypical PR with asymmetrical presentation [5].
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