Section 14. Miscellaneous Inflammatory Disorders

Pityriasis Rosea

Insight

Particularly in patients with darker skin types, pityriasis rosea may be more papular and present in an “inverse pattern” (favoring the body folds such as axillae).

Pityriasis rosea (PR) is a common, benign, self-limited whole body rash with a seasonal prevalence that is clinically characterized by a solitary “herald patch” lesion followed by a whole body exanthem.

Synonyms Pityriasis rosea Gibert, roseola annulata.

Epidemiology

Age 10 to 35 years. Rare in <2 years.

Incidence 2% of all dermatology visits.

Gender F > M, 2:1.

Prevalence Common, especially in fall and spring.

Etiology HHV6 and HHV7 have been postulated, but not proven.

History

A solitary “herald” patch (Fig. 14-1) typically precedes the exanthematous phase by 1 to 2 weeks. The exanthem develops over a period of a week and self-resolves in 6 to 14 weeks without intervention.

Physical Examination

Skin Lesions

Herald Plaque Plaque with collarette of scale (80%).

Exanthem Papules and plaques scale.

Color Pink or red.

Size Herald patch: 1 to 10 cm. Exanthem: 5 mm to 3 cm.

Shape Round to oval.

Arrangement Lesions follow the lines of cleavage in a “Christmas tree” distribution (Fig. 14-2).

Distribution Trunk > proximal arms, legs. Head, face typically spared.

Sites of Predilection Axillae, back, inguinal areas.

General Findings

Headache, malaise, pharyngitis, or lymphadenitis (5%).

Differential Diagnosis

The diagnosis of PR is made on history of herald patch and clinical findings. PR can be confused with tinea, secondary syphilis, guttate psoriasis, tinea, parapsoriasis, pityriasis lichenoides (PL), seborrheic dermatitis, drug eruption (gold, ACE inhibitors, metronidazole, isotretinoin, arsenic, β-blockers, barbiturates, sulfasalazine, bismuth, clonidine, imatinib, mercurials, methoxypromazine, d-penicillamine, tripelennamine, ketotifen, and salvarson), and nummular eczema.

Laboratory Examinations

Dermatopathology Small mounds of parakeratosis, spongiosis, lymphohistiocytic infiltrate.

Course and Prognosis

PR is typically asymptomatic and self-resolves in 6 to 14 weeks. Atypical cases may have severe pruritis, have a more vesicular, purpuric, or pustular presentation, or may last as long as 5 months. Once cleared, it is uncommon for PR to ...