Review Question - QID 108603

The patient’s history of a circular skin lesion presenting a few days prior to acute onset of multiple smaller skin lesions arranged in a Christmas tree pattern on the trunk is highly suggestive of pityriasis rosea (PR) – a reactive skin eruption that often occurs after recent viral infection.

PR is an acute, self-limited, eruption that most commonly affects healthy adolescents and young adults. The classic clinical course begins with a larger circular or ovoid plaque (herald patch), most commonly found on the trunk, followed by multiple smaller ovoid lesions which classically arrange themselves in a Christmas tree pattern on the back (Illustration A). The face, palms, and soles are almost always spared. Most patients are otherwise asymptomatic, although some may have pruritus associated with the lesions. While the exact etiology of PR is unknown, the most frequently cited cause is viral infection with human herpes virus 6 or 7 (HHV-6 or HHV-7). The disease is self-limited and treatment is supportive with topical corticosteroids available for symptomatic patients.

Figure A shows multiple ovoid lesions with fine surface scale distributed in the classic “Christmas tree” pattern. Illustration A shows a crude Christmas tree overlying the eruption of PR. Illustration B shows an annular lesion with associated scale and central clearing that is consistent with tinea corporis or fungal infection of the trunk and extremities. Illustration C shows the target lesions with a dark/dusky red center characteristic of erythema multiforme. Illustration D shows diffuse sloughing of large areas of the skin (> 30% of body surface area) seen in toxic epidermal necrolysis.

Incorrect Answers:
Answer 1: Bacterial infections of the skin typically present with redness, warmth, and pain. Examples of general categories of bacterial skin infections include cellulitis, erysipelas, ecthyma, folliculitis, and abscess formation. Streptococcal pharyngitis can cause an eruption similar to PR known as guttate psoriasis, but this tends to occur in younger children and would not have the classic herald patch or “Christmas tree” distribution seen in PR.

Answer 2: Fungal infections such as tinea corporis (ringworm) can result in circular, scaly lesions which can mimic those seen in PR. In addition, exposures such as wrestling (warm, moist conditions) put certain individuals at higher risk of acquiring the fungal infection. However, the lesions shown in the patient are much more diffuse and lack the central clearing that is characteristic of typical tinea corporis (Illustration B).

Answer 4: Drug reactions are common causes of skin rashes but do not typically present with the fine scaling and distribution characteristic of PR. Drug reactions may range from fixed areas of erythema or discoloration to an exanthematous type reaction (e.g., amoxicillin in a patient with infectious mononucleosis) to annular lesions of erythema multiforme (Illustration C) to Stevens-Johnson syndrome and toxic epidermal necrolysis (Illustration D).

Answer 5: Idiopathic causes of any illness should be considered a diagnosis of exclusion. In this patient, his prior history of sore throat with rhinorrhea and congestion are suspicious for a prior viral infection (even though he was prescribed antibiotics). In light of this, viral infection would be a more likely cause of PR in this patient.

Bullet Summary:
Pityriasis rosea is a reactive skin eruption that classically presents with a herald patch followed by multiple, small, ovoid lesions distributed in a “Christmas tree” pattern on the trunk with sparing of the face, palms, and soles. It is a self-limited condition most frequently associated with viral infection.