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pityriasis rosea

Monday 30 May 2016


Definition : Pityriasis rosea is a self limited viral exanthem usually seen in young patients that starts with a herald patch, followed by similar lesions on the trunk.

The cause of pityriasis rosea is not certain, but its clinical presentation and immunologic reactions suggest a viral infection as a cause. It can be a reactivation of herpes viruses 6 and 7, which cause roseola in infants.




- subacute spongiotic dermatitis
- perivascular lymphocytic infiltrate
- mild acanthosis of the epidermis may be present, especially in herald patch
- foci of parakeratosis overlying spongiosis
- overlying mounds of parakeratosis
- granular layer may be diminished or absent under area of parakeratosis ( hypogranulosis )
- erythrocyte extravasates may be focally present in the superficial dermis
- rare presence of dyskeratotic cells and eosinophils may be observed.

Differential diagnosis

- pityriasis rosea-like eruptions

  • Triggered by medications or vaccinations
  • Clinically, may be itchier, often display peripheral eosinophilia and tend to persist unless the drug is stopped.
  • Microscopy often indistinguishable;
  • may have interface and eosinophilia

- guttate psoriasis / eruptive psoriasis

  • May be very similar clinically and histopathologically
  • herald patch is usually not present in psoriasis
  • neutrophils present in the parakeratosis ;
  • dilated vessels in the papillary plates are more common.

- secondary syphilis:

- Other eczematous eruptions ( contact dermatitis , nummular dermatitis , seborrheic dermatitis ) :

  • May be indistinguishable histopathologically and clinical correlation is required.
  • Although a few eosinophils may be present in pityriasis rosea , large numbers are uncommon.

- drug eruptions

  • Variable clinical presentation
  • Histopathology is variable; combination of interface pattern with spongiosis and eosinophil rich infiltrates are common.

- pityriasis lichenoides :

See also

-  cutaneous anomalies
- pityriaisis