Answer: A

The patient has pityriasis rosea (PR), which can be diagnosed clinically when classic in its presentation as in this case. The characteristic initial lesion that heralds the onset of the eruption is a single oval, sharply-demarcated pink- to salmon-colored plaque usually located on the trunk, but occasionally occurs on an extremity.11 This herald patch typically measures 2 to 5 cm in length and exhibits peripheral scaling with central clearing and slight depression.12,13 A generalized secondary eruption presents 1 to 2 weeks later and consists of smaller, similar-appearing, lesions over the trunk and proximal extremities. Prior to the rash, a prodrome is commonly reported ranging from headache, malaise, pharyngitis, or gastrointestinal symptoms.14

Pityriasis rosea lesions are characteristically oriented so that their long axes run parallel to the cleavage lines of the skin, forming the characteristic Christmas tree pattern that is most apparent on the back and around the axillae.15 Though often asymptomatic, at times the eruption is pruritic.

With a peak age of onset of 10 to 35 years, PR primarily affects adolescents and young adults. Only rarely will children younger than 10 years of age be affected.16 The incidence of PR is thought to be between 0.5% to 2% in the general population, although it may be underdiagnosed.16

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Pityriasis rosea is typically a self-limited, acute exanthem that resolves within 6 to 8 weeks. Scarring is unusual but darker-skinned patients may develop prolonged, though still transient, postinflammatory hyper- or hypopigmentation.

Although lesional morphology and location can vary, the overall presentation and course are similar in most patients. However, it is important to recognize atypical presentations. For example, the herald patch has been reported in unexpected locations, including the sole of the foot.  

Similarly, the generalized eruption may have an uncharacteristic distribution or morphology.  Cases with an unusual distribution are referred to as inverse and often involve the extremities more than the trunk, with variable involvement of the flexural areas. Uncommonly, lesions may be more hemorrhagic, urticarial, vesicular, purpuric, or targetoid.12 Lesion size can also vary, ranging from very small in cases of papular PR, to very large as in Darier PR gigantea.16

Other atypical forms of PR to mention include relapsing PR and persistent PR. Although PR usually resolves spontaneously and recurs rarely, cases that recur within a year of the initial episode and those that persist beyond 12 weeks have been reported.

Making the diagnosis of PR may be difficult if the herald patch cannot be appropriately identified or if the presentation is otherwise atypical. Mimics of the herald patch that may mislead the clinician include tinea corporis and nummular eczema. Similarly, secondary syphilis and pityriasis lichenoides chronica (PLC) can imitate the generalized eruption of PR. Clinical clues such as lesion location or clinical course may help differentiate these conditions. For example, PR typically spares the palms and soles, whereas secondary syphilis generally affects both the palms and soles. A relapsing and recurring course is unusual for PR, but classic for PLC. If the diagnosis is in doubt, additional testing may be necessary to exclude these other conditions. Of note, atypical presentations are more common in the pediatric population than in adults and are easily confused with PLC.2

Biopsy is necessary only in atypical cases, or if an alternative diagnosis is favored. Histologic findings include focal parakeratosis, acanthosis, and spongiosis in the epidermis, and extravasated red blood cells with a dermal infiltrate of various leukocytes.16

PR is believed to be a T-cell mediated process due to increased CD4 T-cells, Langerhans cells, and lack of natural killer cells and B-cells.17 An infectious etiology is suggested by the prodrome of symptoms, occasional clustering in families, and low rate of recurrence. Some even propose the herald patch to represent the inoculation point of a vector.18

Currently, human herpesviruses 6 and 7 (HHV-6 and HHV-7) are believed to be the viruses most closely associated with PR. In fact, HHV-6 and HHV-7 have been detected in patients with PR.13,16 A widely-held theory is that the eruption of PR may occur as an inflammatory response to HHV-6 or HHV-7 reactivation, which may in turn be influenced by other viruses and drugs.16,19

Additional immune-mediated factors have been proposed to somehow affect PR and include a variety of conditions or exposures including atopy, autoimmunity, and various medications.

A PR-like eruption has been described in association with multiple medications including barbiturates, captopril, clonidine, gold, metronidazole, isotretinoin, D-penicillamine, hydrochlorothiazide, allopurinol, and acetylsalicylic acid as well as various vaccines.11,17 Although these PR-like eruptions can be difficult to distinguish from true PR, they are more likely characterized by the presence of more confluent, itchy lesions; extensive involvement of the limbs; peripheral eosinophilia; and lack of prodrome. Histologic changes such as necrotic keratinocytes, dermal eosinophil infiltrate, and perivascular infiltration, which are characteristic of a drug-mediated process, may help to identify cases of drug-induced PR. Discontinuation of the culprit drug should result in prompt resolution.

Patients should be counseled that PR is a benign, minimally contagious, and self-limited process. In general, medications, including antibiotics and antiviral agents, are minimally effective. Phototherapy may have a minor impact as narrowband UV-B (NBUVB) may improve the itch and UV-A1 may reduce rash severity; however, the overall course of the disease is not affected.20 It is reasonable to offer reassurance, observation, and symptomatic relief as the initial therapeutic intervention. However, if the rash persists beyond 2 months, or is more uncharacteristic, other diagnoses and referral to a dermatologist should be considered.16

The patient in this case was counseled regarding the probable diagnosis. Topical triamcinolone cream was prescribed for itch as needed. Re-evaluation 6 weeks later revealed that the eruption was nearly resolved.

Jessica N. Pixley is a 4th-year medical student at Virginia Commonwealth University and a research fellow at Wake Forest School of Medicine Department of Dermatology. Julia R. Nunley, MD, is a professor in the Department of Dermatology at Virginia Commonwealth University in Richmond.


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