Pityriasis rosea (PR) is a common dermatitis that acts like a viral exanthem. Peak incidence is during the second and third decades, although it can occur at any age. Onset is acute and usually consists of the sudden appearance of a single skin lesion, referred to as the herald plaque or patch. About 5% of cases have a prodrome with mild constitutional symptoms, sore throat, GI complaints, and/or cervical adenopathy. In a significant number of patients, the initial lesions are overlooked or occur in hidden locations; therefore, it presents as an acute generalized eruption. Outbreaks often cluster in an epidemic fashion during the spring and fall. This supports speculation of a viral etiology. Cause, however, remains unproven and concurrent cases within family units are rare.
The typical case of PR occurs in three phases. During the primary phase, a solitary lesion or a small group of lesions appears abruptly, usually on the chest or upper torso; however, they can be virtually anywhere, including mucous membranes. These are almost always asymptomatic. This herald plaque enlarges for an average of 7 to 14 days, at which point patients enter the secondary (generalized or exanthematous) phase. This phase lasts an average of 10 to 14 days, during which time smaller versions of the initial lesions develop predominantly over the upper torso and neck along skin cleavage lines. Pruritus may be absent (occasionally), mild (typically), or severe (rarely). The tertiary (regression) phase begins as the progression of new lesions ceases. Over the ensuing 2 weeks, the lesions fade in color, desquamate, and disappear. PR may leave temporary hypopigmentation in some cases, but does not scar and has no permanent sequelae. Recurrent cases are very rare and in most instances an attack confers lifelong protection.
The name pityriasis rosea is descriptive and refers to the rosy-red color of early lesions and the fine branny scale that evolves in the later phase. All PR lesions evolve in a similar way. The earliest lesions, especially the herald plaque, tend to be larger than the later ones (3-4 cm vs 1-2 cm). Early lesions and the herald plaque are usually out of phase with the smaller secondary lesions, and their more advanced morphology aids in the diagnosis. A typical lesion runs its course over a 3- to 4-week period. At onset, lesions start as bright rosy-red papules or plaques that resemble wheals of urticaria. As each lesion approaches its full size, the center darkens and a fine scale occurs. When the central scale loosens, a collarette of white scale is left at the periphery with its free edge characteristically turned toward the center of the lesion. Next the color changes to a dull salmon-pink, the plaque flattens, scales develop over its entire surface, and it disappears.
Musty garments, insect bites, atopic genealogy, and pregnancy are among predisposing factors cited in the older literature. Recent studies, however, fail to confirm these associations.
Patients frequently interpret the herald plaque as a ringworm lesion, so use of proprietary antifungal agents is common. Recently, self-treatment with proprietary hydrocortisone creams has increased. Fortunately neither has any significant effect and does not interfere with the diagnosis.
Intensely pruritic lesions resembling PR, or unusually extensive disease, may signal a PR-like drug eruption rather than actual PR. Associated constitutional symptoms or widespread adenopathy may be a clue that this is really a PR-like syphilid of secondary syphilis. A long-lasting fixed eruption simulating PR has been reported with advanced HIV infection. Under any of these circumstances, a complete general history review is essential.
2. Dermatologic Physical Exam
1. Rosy-red papules (see Photo 18).
2. Rosy-red plaques (see Photo 19)
The earliest lesions are not diagnostic until the central epidermal changes occur. Fortunately few patients come in this early and careful observation will almost always reveal a few with central scale or a peripheral collarette. Small papular primary lesions are more common in pregnant women, young children, and African Americans.
1. Fine, branny, easily dislodged central scale that leaves, as it separates, a characteristic collarette with its free edge pointed to the center of the lesions (see Photo 20).
2. Some patients develop transient hypopigmentation at the lesion sites when resolution is complete.
3. Late lesions desquamate and change from rosy-red to salmon-pink in color. It is not unusual to see the spectrum of lesions in a single patient.
Macrodistribution: Can be quite variable. Classic distribution involves the neck, back, chest, abdomen, proximal arms, hips, and proximal thighs. Face, forearms, palms, and distal lower limbs are usually spared (see Fig. 7).
PR is suppressed by sun exposure; during intense solar exposure lesions may be limited to non-sun-exposed skin only (such as areas beneath bathing trunks or bikinis).
PR has a "Christmas tree" configuration (see Photo 21). When viewed from a distance, the oval lesions of PR classically line up in a linear fashion with their long axes following skin tension lines. Hence, the lesions assume a linear descending pattern much like the drooping branches of a pine tree.
Syphilis serology should be done in all sexually active patients. The lesions of PR and the lesions of secondary syphilis are not clinically distinguishable.
When a solitary scaling plaque or small group of plaques are present, a KOH preparation may be needed to rule out tinea corporis.
There is no specific therapy. PR is essentially a benign self-limiting disease that resolves without sequelae. Treatment is symptomatic.
Patients with moderate or severe itching should be instructed to avoid overheating, take warm but not hot showers, keep bed clothing lighter than usual, and temporarily avoid activity that raises body temperature.
Ultraviolet light suppresses and shortens the duration of the general eruption. Patients who are distressed with extensive lesions can be helped with modest amounts of natural sunlight or ultraviolet B exposure.
A medium potency group IV or V steroid cream or lotion (see Chapter 4, Table 1) is helpful when there is significant itching. Menthol 0.025% can be added for additional relief. The steroid will have no effect on the appearance or duration of the lesions.
Conditions That May Simulate Pityriasis Rosea
Barbiturates, captopril, clonidine, gold, isotretinoin, metronidazole, and penicillamine are among the medications most commonly implicated as causes of eruptions with PR-like morphology. These agents are not exclusive and this possibility should always be considered, especially if the eruption is in any way atypical. The following all suggest a drug eruption:
1. Intense pruritus.
2. Absent herald plaque.
3. An active urticarial component with immediate dermographism.
4. Heavy scale.
5. Evolution of some lesions toward lichen planus-like appearance.
6. Persistence beyond the usual 6- to 8-week course.
Eruptive psoriasis vulgaris (PV) can, in its early stages, be indistinguishable from early PR. This differential must always be considered in a patient with a positive family history for PV. In general, PV will progress unless treated and as the lesions mature they develop the deeper color and loose silvery scale typical of that disease. This differential diagnosis should always be considered with fixed PR. Usually PV lacks a herald plaque and the classic Christmas tree pattern. At this stage, the biopsy findings are generally inconclusive. A short period of observation will usually spare the victim the discomfort, scar, and expense of biopsy.
Early PR with a herald plaque or early cluster of lesions can be difficult to separate from tinea corporis. A simple KOH preparation will distinguish the two, provided the area has not been premedicated with proprietary antifungals.
Generalized SD bears some resemblance to PR. The slow onset, limited lesions, loose scale, and central truncal rather than Christmas tree distribution should serve to distinguish between the two.
This common problem should be clinically separable from PR. The lesions of num-mular eczema are less numerous and differ in morphology. The wet form has a beefy-red moist surface and the dry form has a fissured surface often compared to the crackle finish on oriental pottery. Neither variant of nummular eczema has the Christmas tree distribution. Itching is intense.
This is an important differential in all sexually active persons. Both eruptions can be similar and both can undergo spontaneous resolution. Patients with syphilis usually have associated constitutional symptoms of fatigue, fever, and myalgias. In addition, there are often palmar lesions, mucous membrane lesions, and a generalized adenopathy. A syphilis serology with the same precautions noted above is definitive.
There have been rare reports of a persistent PR-like eruption in cases of late HIV infection. In a single patient observed by one of the authors, the eruption was of gradual onset, had persisted longer than 1 year, and had fixed lesions. Otherwise it simulated the morphology and classic distribution of PR.
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