Tests and diagnosis

By Mayo Clinic Staff

In most cases, diagnosis of psoriasis is fairly straightforward.

  • Physical exam and medical history. Your doctor usually can diagnose psoriasis by taking your medical history and examining your skin, scalp and nails.
  • Skin biopsy. Rarely, your doctor may take a small sample of skin (biopsy) that's examined under a microscope to determine the exact type of psoriasis and to rule out other disorders. A skin biopsy can generally be done in a doctor's office after application of a local anesthetic.

Conditions that can look like psoriasis

Other conditions that may look like psoriasis or may occur at the same time as psoriasis include:

  • Seborrheic dermatitis. This type of dermatitis is characterized by greasy, scaly, itchy, red skin. It's often found on oily areas of the body, such as the face, upper chest and back. Seborrheic dermatitis can also appear on the scalp as stubborn, itchy dandruff.
  • Lichen planus. This is an inflammatory, itchy skin condition that appears as rows of itchy, flat-topped bumps (lesions) on the arms and legs.
  • Ringworm of the body (tinea corporis). Ringworm is caused by a fungal infection on the top layer of your skin. The infection often causes a red, scaly ring or circle of rash.
  • Pityriasis rosea. This common skin condition usually begins as one large spot (herald patch) on your chest, abdomen or back, which then spreads. The rash of pityriasis rosea often extends from the middle of the body, and its shape resembles drooping pine tree branches.
Apr. 11, 2014

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