Pityriasis Rosea: The Daily PANCE Blueprint

The answer is D. Pityriasis rosea

A herald patch followed a week or two later by oval scaly plaques aligned along the skin cleavage lines of the trunk is pityriasis rosea. The two features in that sentence are the whole diagnosis. The herald patch is a solitary, larger, salmon-colored oval plaque with a collarette of fine scale that faces inward toward the center, and it typically precedes the generalized eruption by five to fifteen days — patients often report having been treated for ringworm first, which is a useful history to ask about. The secondary eruption then follows the lines of Langer, producing the classic "Christmas tree" or fir-tree pattern on the back. The condition is self-limited and probably driven by reactivation of human herpesvirus 6 or 7, though it is not considered meaningfully contagious. It is most common in adolescents and young adults, and it resolves spontaneously over six to eight weeks. Management is therefore reassurance plus symptom control: emollients, low-potency topical corticosteroids, and oral antihistamines for pruritus. Set expectations honestly — tell her it will take weeks, not days, and that postinflammatory hyperpigmentation is common and fades, particularly in darker skin. Two clinical points earn their keep. First, always exclude secondary syphilis, which is the great mimic; check an RPR in any sexually active patient, and note that this stem does exactly that. Second, pityriasis rosea in pregnancy, especially in the first twenty weeks, has been associated with an increased risk of fetal loss, so it deserves obstetric awareness rather than pure reassurance. Sorting the distractors, each excluded by a specific feature: tinea corporis is the classic misdiagnosis of the herald patch, but its scale sits on the outer advancing edge rather than as an inward-facing collarette, lesions are usually few rather than dozens, KOH preparation shows hyphae, and it does not follow cleavage lines; guttate psoriasis produces small drop-like plaques with thick silvery scale, typically about two weeks after streptococcal pharyngitis, and it has no herald patch; secondary syphilis gives a diffuse copper-colored papulosquamous eruption that characteristically involves the palms and soles, with constitutional symptoms, generalized lymphadenopathy, and mucous patches or condyloma lata — her palms and soles are spared and the RPR is negative; and nummular eczema forms intensely pruritic coin-shaped plaques, often weeping or crusted, on the extremities of patients with dry skin, with no herald patch and no cleavage-line distribution.