Pityriasis Rosea (cont.)

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How is pityriasis rosea diagnosed?

Pityriasis rosea is usually diagnosed by the skin appearance, particularly the onset of the distinct, large herald patch and the symmetrical Christmas tree presentation. Also, the herald patch tends to have a unique, fine scale with a definite border, the so-called "collarette." To rule out other types of skin disorders, a physician may scrape the skin and use a quick prep fungal test called potassium hydroxide or "KOH" to detect fungus infection that could mimic pityriasis. Also, blood tests including rapid plasma reagent (RPR) may be done to detect secondary syphilis, which also may mimic pityriasis. In some cases, a skin biopsy may be required to detect fungus and other types of rashes.

What are some common misdiagnoses of pityriasis rosea?

The first herald patch of pityriasis rosea may look very similar in appearance to ringworm (tinea corporis). Pityriasis has also been mistaken with eczema and psoriasis, which can occur as similar scaly patches, but not in the same distribution as pityriasis rosea.

Pityriasis rosea may be misdiagnosed as

  • psoriasis,
  • eczema,
  • fungal infection (tinea corporis),
  • secondary syphilis,
  • drug eruption (a diffuse body rash caused commonly by a reaction to a medications like an oral antibiotic),
  • fixed drug eruption (a single small, circular or oval patch of skin rash caused by taking a medication),
  • pityriasis lichenoides chronica,
  • parapsoriasis,
  • HIV-associated rash,
  • folliculitis.
Medically Reviewed by a Doctor on 8/2/2012

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