Pityriasis Rosea

Pityriasis rosea (PR), which means “fine pink scale,” is an acute, benign, self-limiting eruption with a characteristic clinical course.
PR may occur at any age or season, but it tends to occur in older children and young adults in the spring and fall.

The cause is unknown; but a viral etiology with human herpes virus 6 or 7 has been suggested but not confirmed.
The occasional clustering of cases, seasonal appearances and the fact that a single outbreak tends to elicit lifelong immunity supports an infectious, transmissible origin. Repeat episodes are rare, but have been reported.
Despite the prevailing opinion that PR is caused by an infectious agent, it does not appear to be contagious; since household contacts and schoolmates usually do not develop the eruption.

The typical course of PR often begins with the larger herald patch (Fig. 15.1), a 2- to 5-cm, solitary, pink or skin colored scaly patch or thin plaque that may exhibit central clearing and therefore may mimic, and often be confused with, tinea corporis. The herald patch is followed in several days to 2 weeks by numerous characteristic oval or elliptical, “football-shaped” (Fig. 15.2), erythematous thin papules or plaques with fine scale on the trunk, neck, arms, and legs in an “old-fashioned bathing suit” distribution. Individual lesions often develop a thin, circular, collarette of scale surrounding the perimeter of individual patches or within patches in a characteristic “trail of scale” (Fig. 15.3).
Lesions in very dark-skinned patients may lack the typical pink color of PR and may appear darker than the surrounding skin. Itching is usually absent or mild but may be severe in a minority of patients.
The eruption usually lasts for 6 to 8 weeks but may occasionally persist for several months.
On resolution, postinflammatory pigmentary changes (hyper or hypopigmentation) may appear, particularly in dark-skinned people (Fig. 15.4).

PR can occur with less typical presentations such as those in which the herald patch is not noted by the patient or clinician.
In dark-skinned patients, the lesions may be vesicular and uncharacteristically pruritic.
The eruption may be limited in its distribution, or it may present in an inverse fashion involving the groin (Fig. 15.6A,B) axillae, or distal extremities (inverse PR).

The diagnosis is made clinically in most cases.
In general, laboratory tests are not necessary or helpful, with the following exceptions:
1. Early in disease course when only a herald patch is present, a potassium hydroxide (KOH) examination may be helpful to rule in or rule out tinea corporis; later, in disease when numerous lesions are present a KOH may be used to distinguish tinea versicolor (see Chapter 18: Superficial Fungal Infections) from PR.
2. If there is a high degree of suspicion for secondary syphilis, a rapid plasma reagin (RPR) or venereal disease research laboratory (VDRL) test should be performed.
3. A skin biopsy may be performed when the eruption is atypical, the diagnosis is uncertain, or the disease has not resolved after 3 to 4 months.

Differential Diagnosis

Guttate Psoriasis

Small, droplike, 1 to 10 mm in diameter, salmon-pink papules, usually with a thicker scale than PR.

Secondary Syphilis

Tinea Versicolor

Tinea Corporis

Drug Eruption

Infrequently, drug eruptions secondary to barbiturates, bismuth, captopril, clonidine, diphtheria toxoid, gold, isotretinoin, ketotifen, levamisole, metronidazole, and D-penicillamine can resemble PR.

Viral Exanthem

Nummular Eczema

Parapsoriasis

Chronic skin condition characterized by round or oval, red, slightly scaly patches on limbs and trunk.
Mostly affects adults.
Patches often exhibit cigarette paper-like wrinkling.

Management

Treatment is often unnecessary, because PR is a self-limiting, asymptomatic condition that resolves with no sequelae.
Patients should be educated about the usual course of the rash and its noncontagious nature.
Exposure to sunlight or administration of ultraviolet B by a dermatologist may speed resolution of the eruption.
Follow-up or referral to a dermatologist should be made if the rash persists more than 8 weeks.
In cases of severe pruritus, oral antihistamines or mid potency topical steroids such as triamcinolone 0.1% cream may help alleviate the itching.
On occasion, systemic steroids (prednisone, 0.5 to 1 mg/kg/day for 7 days) may be used in patients with severe pruritus.
Oral erythromycin or azithromycin has been reported to shorten the course of the eruption in some cases.

Points to Remember

Lesions characteristically appear “from the neck to the knees,” in a “Christmas tree” distribution.
PR is observed in otherwise healthy people, most frequently in children and young adults.
Patients should be told that PR is a benign condition that will resolve without treatment.
Secondary syphilis should be considered in the differential diagnosis, especially when lesions are also present on the palms and soles.

Distribution of Lesions

The herald patch is most commonly observed on the trunk, neck, or extremities. The absence of the herald patch does not necessarily rule out the diagnosis; it may be absent or hidden in an obscure location such as the scalp or groin.
The long axis of the lesions runs parallel to skin tension lines. This gives a so-called “Christmas tree” pattern on the trunk (Figs. 15.4 and (15.5).