Pathophysiology: The specific cause of the disorder remains unclear. The seasonal occurrence, clinical course, ability to occur in epidemics, presence of occasional prodromal symptoms, and infrequent likelihood of recurrences have all suggested an infectious etiology. The disease has been associated with recent upper respiratory infections. Reports of increased incidence exist among groups with close physical contact (eg, families, students, the military) that suggest a transmissible agent. A higher incidence exists among patients with decreased immunity (eg, pregnant women, bone marrow transplant patients). Additionally, ampicillin has been noted to increase the distribution of the eruption; this phenomenon bears a striking resemblance to ampicillin's effect on the rash of infectious mononucleosis. Many common infectious agents have been studied (eg, influenza A and B; parainfluenza I, II, III; Mycoplasma) and shown not to be causative. Recent reports using polymerase chain reaction (PCR) analysis have suggested a role for human herpesvirus-7 (HHV-7), but this has not been confirmed in later studies.

Despite the prevailing opinion that PR is caused by an infectious agent, it does not appear to be very contagious; household contacts and schoolmates usually do not develop the disease.

Pityriasis rosealike eruptions also can occur in association with many drugs. These include barbiturates, bismuth, captopril, clonidine, diptheria toxoid, gold, isotretinoin, ketotifen, levamisole, metronidazole, and D-penicillamine. Drug-induced PR often lasts for a longer time than non–drug-induced PR.

Frequency:

• Internationally: PR is present worldwide and occurs year-round, though it may be more common in the fall and spring.

  PR accounts for approximately 2% of outpatient visits in dermatology.

Mortality/Morbidity:

• PR is a self-limiting benign disorder with a recurrence rate of less than 3%. It usually lasts for 6-8 weeks, but can last as long as 3-6 months. Postinflammatory pigment changes are common, especially in African Americans. Bacterial superinfections rarely are observed.

Race: PR shows no racial specificity, although African Americans may have more extensive or atypical disease.

Sex: PR occurs slightly more often in females than in males. The female-to-male ratio is reported as 2:1 or 3:2 in the US.

History:

• A small number of patients (5%) have mild prodromal symptoms, such as fatigue, headache, nausea, anorexia, chills, and arthralgias. Lymphadenopathy may occur prior to onset of the rash.

• Patients may have a history of recent upper respiratory infection (URI) (8-20%).

• Rash may be pruritic (25-75%), especially in the first few weeks of the illness.

• Approximately 50-80% of patients present with a herald patch.

Physical:

• Primary herald patch

• A herald patch is a pink macule or papule that gradually expands over a few days to become a 2- to 10-cm, salmon-pink to brown, oval plaque. The lesion is scaly and may exhibit central clearing, which mimics tinea corporis.

• Primary herald patch is most commonly observed on the trunk, neck, and proximal extremities.

• Subsequent lesions

• Numerous subsequent lesions occur in crops 1-2 weeks (range 1-30 d) after onset of the herald patch and usually involve the thorax, back, abdomen, and proximal extremities. The lesions usually are not observed on the face, hands, and feet.

• These lesions are macular or papular, elliptical or oval in shape, and 0.5-1.5 cm across. A fine scale usually is present. A characteristic feature is a collarette appearance to the scale, with the edges of the scale attached peripherally and lifted up near the center of the lesion. However, unlike classic tinea corporis, the scale does not extend to the edge of the lesion.

• Lesions are distributed diffusely, and the long axis of the lesions runs parallel to skin tension lines. This gives a Christmas tree pattern on the back.

• With resolution of the eruption, postinflammatory pigment changes can be observed.

• Oral lesions: Oral lesions are observed infrequently but may include plaques, petechiae, and ulcers (with or without raised borders).

• Variants and atypical forms

• Approximately 20% of patients present with atypical forms of PR.

• A predominantly papular form is believed to occur more commonly in young children, pregnant women, and African Americans.

• Lesions of the face, hands, and feet occasionally are observed. Facial lesions may be observed more commonly in the same group as mentioned above. The physician should consider secondary syphilis in the differential diagnosis especially when lesions are present on the palms and soles.
• Lesions can be vesicular, pustular, urticarial, purpuric, or even erythema multiformlike, making the diagnosis difficult.

• An inverse pattern also is observed, with most of the lesions occurring on the face and extremities.
• Secondary eczematous changes can occur if pruritus is severe.

• African Americans tend to have a widespread form with hyperpigmentation upon resolution.

Lab Studies:

• The diagnosis is made clinically in most cases. In general, lab tests are not necessary or helpful, with the following exceptions:

• A potassium hydrochloride (KOH) test may be especially helpful when only the herald patch is present, to help diagnose tinea corporis.

• If the eruption includes lesions on the hand and feet, or the patient is sexually active, than a rapid plasma reagin (RPR) or venereal disease research laboratory (VDRL) test should be done to rule out secondary syphilis. Other features that would suggest syphilis include patchy alopecia, salmon colored plaques on the palms and soles, diffuse adenopathy, white papules of the oral mucosa, and condylomata lata.

• A skin biopsy can be done when the eruption is atypical, the diagnosis is uncertain, or the disease has not resolved after 3-4 months. It will show nonspecific features of a subacute or chronic dermatitises, but may be helpful to rule out other diseases in the differential diagnosis.

Medical Care:

• Treatment is unnecessary in most cases, since PR is usually a self-limiting disease with no sequelae. Patient education and reassurance is all that is needed.

• In cases of severe pruritus, various measures may be taken to provide symptomatic relief:

• Patients should avoid harsh soaps, tight clothing, and scratching.
• Bland emollients may be helpful. Topical preparations with calamine, menthol, pramoxine, colloidal starch, and oatmeal also may be beneficial.
• Oral antihistamines or topical steroids may help alleviate the pruritus. The sedative effect of the antihistamines may help the patient to sleep better at night. On occasion, systemic steroids (prednisone 0.5-1 mg/kg/d for 7 d) can be used in patients with severe pruritus. Some dermatologists also will use systemic steroids in cases with vesicular lesions, or if there is concern for significant postinflammatory hyperpigmentation. Systemic steroids in large doses will suppress pruritus and exanthem but not shorten the course of the disease. Systemic steroids may exacerbate the disease in some patients. Short courses of dapsone have been used in severe bullous PR unresponsive to systemic steroids.

• UV-B (5 daily erythemogenic doses) may relieve pruritus in as little as 24 hours, but may increase incidence of postinflammatory hyperpigmentation. Natural sunlight in reasonable amounts may be helpful.

Consultations: Patients with severe pruritus, disease requiring systemic steroids, or those for which UV-B therapy is desired, should be referred to a dermatologist.

Treatment should not be necessary because PR is usually a self-limiting disease with no sequelae. In cases of severe pruritus, oral antihistamines can be used for their sedating effect in attempt to prevent scratching at night. Topicals may be beneficial to soothe and moisturize the skin (eg, calamine lotion, zinc oxide, menthol-phenol preparations, colloidal starch, oatmeal).
 

Drug Category: Antihistamine -- Used for its sedating effect to decrease scratching at night. Act by competitive inhibition of histamine at the H1 receptor.

Drug Category: Corticosteroids, topical -- Over-the-counter low-to-medium potency steroids may help relieve itching. Elicits anti-inflammatory and immunosuppressive properties.

Further Outpatient Care:

• PR is a self-limiting disease and no follow-up is necessary in most cases.

• Patients with moderate-to-severe pruritus who are receiving topical steroids should have follow-up by phone or by a return visit in 1-2 weeks.

Complications:

• Bacteria rarely may secondarily infect the lesions. Postinflammatory hyperpigmentation is the most common long-term complication.

Prognosis:

• Prognosis is excellent. The recurrence rate is approximately 2%.

Patient Education:

• Patients need to be told that PR is a benign disease that will resolve over the next 6-12 weeks without treatment. Lesions do not result in scars, though postinflammatory pigment changes can occur. Patients should be told that PR is possibly minimally contagious but that no specific infectious precautions are necessary.