Pityriasis Rosea - Diagnosis

Diagnosis

Experienced practitioners may make the diagnosis clinically. 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, and especially secondary syphilis. A biopsy of the lesions will show extravasated erythrocytes within dermal papillae and dyskeratotic cells within the dermis.

A set of validated diganostic criteria for pityriasis rosea is as follows:

A patient is diagnosed as having pityriasis rosea if:

1. 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 2. 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: 1. Discrete circular or oval lesions, 2. Scaling on most lesions, and 3. Peripheral collarette scaling with central clearance on at least two lesions.

The optional clinical features are: 1. Truncal and proximal limb distribution, with less than 10% of lesions distal to mid-upper-arm and mid-thigh, 2. Orientation of most lesions along skin cleavage lines, and 3. 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:

1. Multiple small vesicles at the centre of two or more lesions, 2. Two or more lesions on palmar or plantar skin surfaces, and 3. Clinical or serological evidence of secondary syphilis.