Diagnosis: Inverse pityriasis rosea

This patient had pityriasis rosea, an acute inflammatory dermatosis of unknown etiology. Viruses, particularly human herpesvirus 6 and 7, have been suggested as the causative pathogen, but study results have not been definitive.

Pityriasis rosea is common among Americans, with more than 5% of the U.S. population affected. Gender prevalence is a 1.5:1 ratio of females to males. Patients are typically children and young adults, with incidence peaking during the second decade. In a study of patients in Minnesota, 75% were between 10 and 35 years of age (range 10 months to 78 years; mean age 22.7).1 Cases occur most frequently during the spring, but lesions can develop during any time of the year. 

Presentation of pityriasis rosea follows a classic natural history. Commonly, a single large plaque appears on the scapular area. The characteristic herald lesion is usually red or brown and bordered by a fine scale. This is followed by development of smaller oval lesions along Langer’s lines. On the back, the lesions develop in a “Christmas tree” pattern. On other areas, they follow the cleavage lines, i.e., transversely across the abdomen, around the shoulders, and in a V-shaped pattern on the chest. Inverse disease occurs when the extremities or intertriginous areas are affected but the trunk is spared. Eruptions normally last five to eight weeks; however, 25% of cases last for up to 12 weeks. Pruritus is found in 75% of cases; one quarter of these are severe. 

A number of conditions can be confused with pityriasis rosea, including guttate psoriasis, erythema annulare centrifugum, secondary syphilis, nummular dermatitis, drug eruptions (particularly reactions to heavy metals, most commonly gold), Gianotti-Crosti syndrome, tinea corporis, pityriasis lichenoides parapsoriasis, and cutaneous lupus. Diagnosis is usually clinical and does not require biopsy. An RPR test should be done to rule out syphilis. Guttate psoriasis patients will have an elevated ASLO. Tinea is ruled out by absence of hyphae on a KOH preparation. 

Inverse pityriasis is rare. In one study of 368 patients with pityriasis rosea, inverse distribution involving mainly the extremities was seen in 22 cases (6%).2 A second study of 50 affected patients found inverse disease in 2% of cases.3 The differential diagnosis of inverse pityriasis rosea includes inverse psoriasis, inverse lichen planus, intertrigo, axillary granular parakeratosis, variants of pemphigus, Hailey-Hailey disease, Darier’s disease, and candidiasis. No difference in morbidity or disease outcome has been observed between the inverse and the usual distributions.

Because pityriasis rosea is self-limiting, the role of treatment is unclear. Therapy is typically initiated to eliminate associated pruritus, with oral antihistamines and topical corticosteroids most frequently used. 

In one prospective, blinded, placebo-controlled study of 90 patients, complete clearance of lesions was seen in 73% of those who received a two-week course of erythromycin four times daily.4 In the same study, no clearance was seen in those who received placebo. The effect of erythromycin may be linked to its anti-inflammatory properties. Reports have also suggested that acyclovir (800 mg five times daily) can shorten disease duration. In one series, azithromycin was no better than placebo in shortening duration of pityriasis rosea in children. Severe disease may be treated with phototherapy. Recurrence is seen in 1.8% of patients after an average 4.5 years of follow-up.1 In patients of color, cleared lesions can leave behind dark brown macules. 

Our patient was prescribed azithromycin (Zithromax) 500 mg for one day and 250 mg for four days. Tacrolimus (0.1%) ointment (Protopic) was to be applied twice daily to the axillae. Eight weeks later, the eruption had resolved.    

Dr. Scheinfeld is chief of pediatric dermatology and chief of clinical trials in the Department of Dermatology at Metropolitan Hospital/New York Medical College in New York City and assistant clinical professor of dermatology at Columbia University, also in New York City.

References

1. Chuang TY, Ilstrup DM, Perry HO, Kurland LT. Pityriasis rosea in Rochester, Minnesota, 1969 to 1978. J Am Acad Dermatol. 1982;7:80-89.
2. Tay YK, Goh CL. One-year review of pityriasis rosea at the National Skin Centre, Singapore. Ann Acad Med Singapore. 1999;28:829-831.
3. Egwin AS, Martis J, Bhat RM, et al. A clinical study on pityriasis rosea. Indian J Dermatol. 2005;50:136-138.
4. Sharma PK, Yadav TP, Gautam RK, et al. Erythromycin in pityriasis rosea: a double-blind, placebo-controlled clinical trial. J Am Acad Dermatol. 2000;42 (2 pt 1):241-244.