As the condition is typically a self-limiting disorder, with seasonal clustering, predominance during cold or winter months [7, 9, 11, 15–17, 19], and few recurrences, it is thought to be due to an infection, usually precipitated by an upper respiratory tract infection, with long-lasting immunity [4, 8, 15]. Many infective agents have been implicated, e.g., Influenza A, H1N1 [20, 21], cytomegalovirus [22], Epstein–Barr virus [23], parvovirus B19 [24] and Mycoplasma pneumoniae [25]. However, prospective studies have failed to show a significant change in serological titers in acute and convalescent stages for mycoplasma, cytomegalovirus, Epstein–Barr virus and parvovirus B19 [26, 27]. There are reports of the association of human herpesvirus-7 (HHV-7) with polymerase chain reaction (PCR) analysis and less so human herpesvirus-6 (HHV-6) with pityriasis rosea [28–31]. But they remain controversial [32–34].

A herald patch, which is a single isolated lesion, can be found classically on the trunk but can also occur on the upper arm, neck, or thighs. The herald patch is seen in 17–94 % of cases [5, 26]. This oval patch varying from about 1 to 10 cm with collarette scaling can be mistaken for tinea corporis or eczema. Approximately 5 % of patients may feel a mild prodrome of headache, fever, malaise, or arthralgias [35]. Within a few days after the herald patch, there is a subsequent secondary eruption over the trunk and proximal extremities of lesions in a T-shirt and shorts distribution with peripheral collarette scaling (Figs. 33.1 and 33.2) which has been reported to be enhanced by epiluminescence dermatoscopy [36].

The orientation of these lesions on the posterior trunk is referred to as a “fir tree” or “Christmas tree” pattern [37]. “Langer’s cleavage lines” is now proposed to be the most appropriate term with the V-shaped pattern on the upper chest and back, circumferential pattern around the shoulders and hips, and transverse pattern on the lower anterior trunk and lower back (Fig. 33.3) [38]. Atypical forms of pityriasis rosea include an inverse pattern where the face and extremities are affected more than the trunk [39]. African patients have been reported to have a more extensive rash with more frequent involvement of the face and scalp [6]. It has been reported to present in the scalp in children [40] and when presenting on the soles can mimic secondary syphilis [41]. Other atypical forms of presentation include a vesicular eruption [42], erythema multiforme-like rash [43], urticarial [44], and purpuric variants [44, 45].

As the condition is self-limiting in about 6–8 weeks, treatment may not be necessary (Table 33.2). However, pruritus can be bothersome and oral antihistamines and topical corticosteroids may be helpful. These provide symptomatic relief but do not help in the clearance of the rash [46]. Systemic steroids have not been shown to be effective [46, 47]. Exposure to UV-B therapy starting at 80 % of the minimum erythrogenic dose may relieve pruritus in as little as 24 h but may increase the incidence of post-inflammatory hyperpigmentation [48–50]. Alternatively, low-dose (10–30 J/cm²) UV-A1 phototherapy given 2–3 times a week until resolution may be tried [51]. Early administration of erythromycin 1 g taken orally in four divided doses for adults or 25–40 mg/kg divided four times daily in children for 2 weeks in a double-blind placebo controlled trial led to early resolution of symptoms [52]. However, subsequent studies did not find erythromycin or azithromycin useful [53, 54]. There is some evidence that oral acyclovir 1 g five times a day for 7 days at the onset in adults has been shown to shorten the duration of the disease [55, 56]. Subsequently, lower dosages of acyclovir 400 mg five times a day for 1 week was shown to be equally effective [57]. Recent studies have shown that despite its effectiveness in herpes simplex virus infection, acyclovir was not as effective as ganciclovir and forcarnet against HHV-6 and 7 [58]. This is because acyclovir is thymidine kinase-dependent whereas HHV-7 lacks the thymidine kinase gene [59]. There are yet to be published data on the effectiveness of ganciclovir and forscarnet in pityriasis rosea.