What May Resemble Psoriasis?
Generalized Disease - Psoriasis
Pityriasis rosea is a condition seen in people between the ages of 10-35 years of age. In contrast to psoriasis, it often starts with a solitary large "Herald Patch" before multiple smaller lesions develop. In pityriasis rosea, the lesions are generally thinner with less scale. The face, palms and soles are not usually involved.
Tinea corporis is a fungal infection on the body. Red scaly patches may be seen, but unlike psoriasis, the centers of the patches often show clearing. The edges have scaling (which is usually not as thick as in psoriasis) and may also have pustules. A fungal culture is usually positive.
In psoriasis, there is usually much more scale and the patches are generally larger and red in contrast to lichen planus, which has smaller purple lesions with less scale. In lichen planus, the flexural areas, particularly the wrists, are affected, while in the psoriasis the extensor areas (such as the elbows) are affected.
In secondary syphilis, a generalized rash similar to psoriasis may be seen, however, blood tests for syphilis are usually positive.
Mycosis fungoides is a T cell lymphoma in the skin. The lesions tend to be chronic, but lack the thick, silvery scales that are seen in psoriasis.
On Your Palms and Soles
Hand and foot dermatitis
Pustulosis palmaris and plantaris may look similar to dyshidrotic eczema, however, in the latter, blisters rather than pustules (unless there is a secondary infection) are seen on the sides of the fingers, toes, palms and arches of the feet.
Tinea pedis is a fungal infection of the soles of the feet that usually starts in the lateral web spaces, then spreads to the soles. Nails may be secondarily infected and look very similar to psoriasis. A fungal culture will usually be positive in this condition. In psoriasis, the scales on the soles are usually thicker and more well defined and the fungal culture is negative.
What Else Looks Like Scalp Psoriasis?
In seborrheic dermatitis, the scales are usually yellow rather than white and well defined patches are not usually seen. The eyebrows and cheeks next to the nose may be involved, and the elbows and knees (which are commonly involved in psoriasis) are not affected. In psoriasis, the lesions often extend beyond the hair border onto the face or neck.
In scalp fungal infections, the hair is often broken, hair loss and pustules may be seen and a fungal culture is usually positive.
In lupus erythematosus, the lesions are usually more purple in colour, the skin may be thinned, scaling is more prominent around the hair follicles and hair loss is common.