Pityriasis rosea is clinically characterized by a herald patch or mother patch followed by scaly oval plaques on the trunk and proximal extremities along the Langer’s lines of cleavage giving characteristic “Christmas-tree" appearance. Collarette scaling is common. The eruption is usually preceded by a prodrome of a sore throat, gastrointestinal disturbance, fever, and arthralgia.

Pruritus is severe in 25% of cases. Herald patch is seen in 50% to 90% cases and is located on the trunk followed by the neck or proximal extremity.

A generalized eruption then occurs, in which numerous lesions develop in crops over a period of one to two weeks after the onset of the herald patch. The eruptions are symmetric and most commonly involve the thorax, back, abdomen, and adjoining areas of the neck and extremities. These secondary lesions occur as macules and papules that are elliptical or ovular in shape. Fine scaling and central wrinkling, with a cigarette paper aspect, are seen. A characteristic feature is the collarette appearance of the scale, with edges peripherally attached and lifted up near the center of the lesion. The distribution of the lesions is usually bilateral and diffuse, with the long axis running parallel to skin tension lines.

The incidence of atypical pityriasis rosea is 20% which may be in regard to morphology, size, distribution, course, or symptoms.

The various atypical morphologies include:

• Vesicular Pityriasis Rosea presents as a generalized eruption of 2 mm to 6 mm vesicles or as a rosette of vesicles mainly over the head, palms, and soles. It needs to be differentiated from varicella and dyshidrosis. It is commonly seen in children.
• Purpuric (hemorrhagic) Pityriasis Rosea presents as macular purpura on skin or oral mucosa.
• Urticarial Pityriasis Rosea
• Generalized Papular Pityriasis Rosea is rare and is seen in young children, pregnant women, and African Caribbeans. It presents as multiple papules that occur along with classic patches and plaques.
• Lichenoid Pityriasis Rosea is observed in the course of atypical Pityriasis Rosea, but it is more commonly caused by drugs such as gold, captopril, barbiturates, D-penicillamine, and clonidine.
• Erythema multiforme-like Pityriasis Rosea: It presents with targetoid lesions along with the classical lesions of pityriasis rosea. Histopathologically, erythema multiform and pityriasis rosea may show similar features except for satellite cell necrosis which is a distinguishing feature seen only in erythema multiform where lymphocytes are seen attached to scattered necrotic keratinocytes.
• Follicular Pityriasis Rosea: The secondary lesions are typically follicular and present discrete or in groups associated with classical lesions. Differential diagnoses include follicular lichen planus and keratosis pilaris ad atopic dermatitis with a follicular element.
• Giant Pityriasis Rosea is rarely reported and was named after Darier. It consists of plaques and circles of very large sizes ranging from 5 cm to 7 cm with individual lesions reaching the size of the palm of the patient.
• Pityriasis Rosea presenting as exfoliative dermatitis
• Pityriasis Rosea with atypical herald patch may be absent in 20% of patients or present with secondary eruptions or occur at unusual sites such as the face, scalp, genitalia, or other sites.
• Inverse Pityriasis Rosea: Lesions are predominantly present in acral and flexural areas involving axilla, groin, and face.
• Acral Pityriasis Rosea: Lesions are more concentrated over acral parts of body ie palms and soles, where EM, syphilis, necrolytic acral erythema, and drug eruptions should be kept as differentials.
• Unilateral Pityriasis Rosea is a rare variant that can be seen in both children and adults, and the lesions are located on one side of the body. The patient has a herald patch with classical secondary lesions.
• Blaschkoid Pityriasis Rosea: Lesions of Pityriasis Rose follows the lines of Blaschko.
• Limb-Girdle Pityriasis Rosea: Also known as Pityriasis Rosea of Vidal where eruptions are limited to shoulders or pelvic girdle, thus involving axilla and groin. Lesions are usually larger and more annular.
• Mucosal involvement in pityriasis rosea is seen in 16% of patients affecting oral mucosa, with punctuate, erosive, bullous, hemorrhages, ulcers (with or without raised borders), petechiae, papulovesicular, bullae, and erythematous plaques.
• Localized pityriasis rosea: Eruptions are localized to one part of the body.

The rashes of pityriasis rosea usually last for five weeks and resolve by 8 weeks in more than 80% of patients. Pityriasis rosea needs to be differentiated from secondary syphilis, dermatophytosis, guttate psoriasis, nummular eczema, pityriasis lichenoid chronic, cutaneous T-cell lymphoma, erythema annular centrifugal and erythema chronic migrans.

Dermatoscopy helps to differentiate pityriasis rosea from other conditions. It shows a yellowish background color, a peripheral arrangement of the scales, and a patchy distribution of loosely arranged dotted vessels.

Histopathology shows superficial perivascular dermatitis. Focal parakeratosis in mounds, hyperplasia, and focal spongiosis are observed in the epidermis. The epidermis may show exocytosis of lymphocytes, variable spongiosis, mild acanthosis, and a thinned granular layer. Extravasated red blood cells along with a perivascular infiltrate of lymphocytes, histiocytes, and eosinophils are seen in the dermis.[2][8][9]

Pityriasis rosea is a self-limiting, exanthematous disease. Most patients need emollients, antihistaminics, and topical steroids. Macrolides and acyclovir lead to faster resolution of lesions and help to relieve pruritus. Narrowband ultraviolet B therapy is also used. It works by altering the immune response in the skin.[10]

• Erythema multiforme 

• Guttae psoriasis

• Kaposi sarcoma

• Lichen planus

• Parapsoriasis

• Pediatric syphilis

• Pityriasis alba

• Seborrheic dermatitis

• Tinea corporis

• Tinea versicolor

Atopy is associated with pityriasis rosea. Pityriasis rosea during pregnancy, within the first 15 weeks of gestation, may cause premature delivery and fetal demise.

In the majority of patients, pityriasis is a self-limited condition with an excellent prognosis. However, about 2-3% of patients will experience a recurrence. The skin disorder is benign, non-contagious and does not require any special precautions. Since the majority of patients first present to their primary care provider when the skin lesions appear, it is important for the nurse, pharmacist and primary care provider to educate the patient that the condition is benign and will not last for more than 2 months. For cases that are severe, a dermatology referral should be made. The biggest morbidity is due to pigmentation changes, especially in dark-skinned individuals. However, scarring does not occur. There are reports that pityriasis during pregnancy may be associated with premature birth- but it is not known if this is just a coincidental observation. Patients should be told to avoid applying irritants to the skin and avoid tanning. The itching is mild and usually resolves with a moisturizer. Exposure to the sun may induce pigmentary changes and should be avoided. [11][12] (Level V)