CHICAGO (FRONTLINE MEDICAL NEWS) – Pityriasis rosea was recognized as early as 1798, yet its precise cause remains elusive.

“We still don’t have a lot of information on it, because it’s self limited and it resolves,” John C. Browning, MD, said at the World Congress of Pediatric Dermatology. “There hasn’t been quite as much of a burning push for research into pityriasis rosea as there has been for pityriasis rubra pilaris, for instance.”

Classic pityriasis rosea (PR) is characterized by oval scaly, erythematous lesions on the trunk and extremities, sparing the face, scalp, palms, and soles, said Dr. Browning , a pediatric dermatologist who is chief of dermatology at the Children’s Hospital of San Antonio, Texas. The hallmark sign is a so-called herald patch, an oval, slightly scaly patch with a pale center, which usually appears on the trunk and remains isolated for about 2 weeks before the generalized papulosquamous eruption begins. This typically lasts for about 45 days but can range from 2 weeks to 5 months.

“The herald patch is often mistaken for tinea corporis,” Dr. Browning said. “With the wide variability of over-the-counter antifungals, often these patients have used a topical antifungal agent on their own, or they’ve seen a primary care physician who’s prescribed one, and they’re not seeing an improvement.” Atypical cases also occur, often involving oral lesions.

Symptoms of PR may include malaise, nausea, loss of appetite, headache, difficulty concentrating, irritability, gastrointestinal upset, upper respiratory symptoms, joint pain, lymph node swelling, sore throat, and low-grade fever. Pruritus is variable, both in frequency and in intensity, and can be exacerbated by topical medications. Some studies have found a higher female-to-male ratio, while other studies have shown no such association.

“Only 6% of PR cases have been reported in children under 10 years of age,” Dr. Browning said. “PR in dark-skinned children tends to have more facial involvement and a scaly appearance, compared with lighter-skinned children.”

Human herpesvirus (HHV) 6 and HHV 7, members of the Roseolovirus genus of HHVs, have been implicated in triggering PR. These viruses cause a primary infection and can establish latent infection with reactivation if altered immunity develops.

“That’s probably why we don’t see PR in younger children, because that’s when the primary infection is happening,” Dr. Browning said. “These viruses are commonly acquired during childhood, with adult seroprevalence in the range of 80%-90%. Latency occurs in monocytes, bone marrow progenitor cells, in salivary glands, the brain, and in the kidneys, so it’s pretty widespread.”

He added that controversy exists as to whether HHV 6 and 7 cause PR, because older diagnostic methods only detected the presence of HHV DNA, rather than viral load. “HHV reactivation, rather than primary infection, is more likely the cause of PR as supported by sporadic occurrence of PR, reduced contagiousness, age of PR onset, possible relapse during a limited span of time, and frequent occurrence after stress or immunosuppressive states such as pregnancy,” Dr. Browning said.

Classical presentations of PR are not clinically worrisome, but atypical cases could indicate other triggers, such as drug-induced PR. “This is typically more itchy, can have mucous membrane involvement, and you’re not going to see the herald patch,” he said. “It’s more likely to be confluent with no prodromal symptoms.” Agents that have been implicated in drug-induced PR include isotretinoin, terbinafine, and adalimumab.

Other conditions that can trigger PR include secondary syphilis (characterized by involvement of the palms and soles, lymphadenopathy, and greater lesional infiltration); seborrheic dermatitis (characterized by greater involvement of the scalp and other hairy parts of the body); nummular eczema (more pruritic); and pityriasis lichenoides chronica, which involves more chronic and relapsing lesions. Histology of PR reveals focal parakeratosis in the epidermis in mounds with exocytosis of lymphocytes, variable spongiosis, mild acanthosis, and a thinned granular layer.

Dr. Browning noted that PR is more common in pregnancy. One study of 38 pregnant women with PR found that 13% miscarried before 16 weeks, compared with a normal miscarriage rate of 10% ( J Am Acad Dermatol. 2008 May; 58[5 Suppl 1]:S78-83 ). “Neonatal hypotonia, weal motility, and hyporeactivity have been reported,” he said. “And with immunocompromised patients, you might see a longer, protracted course of PR.”

Although no treatment is recommended for classical cases of PR, Dr. Browning said that topical steroids “are widely employed because we all want to do something, especially if there’s some pruritus.” According to a position statement on the management of patients with PR, erythromycin has been reported to shorten the duration of rash and pruritus, but it can cause gastrointestinal disturbance ( J Eur Acad Dermatol Venereol. 2016 Oct;30[10]:1670-81 ). Acyclovir has been reported to hasten clearance of PR in one placebo-controlled study, but PR has also been reported in another patient taking low doses of acyclovir. Phototherapy has also been found to be beneficial.

Dr. Browning reported having no financial disclosures.