page_title: Pityriasis rosea
section_title: Diagnosis
hierarchical_section_title: Pityriasis rosea / Diagnosis
caption_attribution_description: English: A herald patch of pityriasis rosea
context_page_description: Pityriasis rosea is a type of skin rash. Classically, it begins with a single red and slightly scaly area known as a "herald patch". This is then followed, days to weeks later, by a rash of many similar but smaller round or oval lesions, mainly on the trunk and upper limbs. About 20% of cases show atypical deviations from this pattern. It usually lasts less than three months and goes away without treatment. Sometimes malaise or a fever may occur before the start of the rash or itchiness, but often there are few other symptoms.
  While the cause is not entirely clear, it is believed to be related to human herpesvirus 6 or human herpesvirus 7. It does not appear to be contagious. Certain medications may result in a similar rash. Diagnosis is based on the symptoms.
  Evidence for specific treatment is limited. About 1.3% of people are affected at some point in time. It most often occurs in those between the ages of 10 and 35. The condition was described at least as early as 1798.
context_section_description: Experienced practitioners may make the diagnosis clinically. Classical symptoms are usually straightforward to recognize, but the wide range of atypical forms may cause difficulty for the clinician in diagnosing some cases. Misdiagnosis by nondermatologists is not uncommon. If the diagnosis is in doubt, tests may be performed to rule out similar conditions such as Lyme disease, ringworm, guttate psoriasis, nummular or discoid eczema, drug eruptions, other viral exanthems. The clinical appearance of pityriasis rosea in some cases is similar to that of secondary syphilis, and rapid plasma reagin testing should be performed if there is any clinical concern for syphilis. A biopsy of the lesions will show extravasated erythrocytes within dermal papillae and dyskeratotic cells within the dermis.
  A set of validated diagnostic criteria for pityriasis rosea is as follows:
  A patient is diagnosed as having pityriasis rosea if:
  On at least one occasion or clinical encounter, he / she has all the essential clinical features and at least one of the optional clinical features, and
  On all occasions or clinical encounters related to the rash, he / she does not have any of the exclusional clinical features.
  The essential clinical features are the following:
  Discrete circular or oval lesions,
  Scaling on most lesions, and
  Peripheral collarette scaling with central clearance on at least two lesions.
  The optional clinical features are the following:
  Truncal and proximal limb distribution, with less than 10% of lesions distal to mid-upper-arm and mid-thigh,
  Orientation of most lesions along skin cleavage lines, and
  A herald patch (not necessarily the largest) appearing at least two days before eruption of other lesions, from history of the patient or from clinical observation.
  The exclusional clinical features are the following:
  Multiple small vesicles at the centre of two or more lesions,
  Two or more lesions on palmar or plantar skin surfaces, and
  Clinical or serological evidence of secondary syphilis.
caption: A herald patch of pityriasis rosea which started before the rest of the lesion and was initially mistaken for a fungal infection
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