Rashes That Mimic Psoriasis in Different Areas of the Body

Differential Diagnosis of Psoriasis - What Else Could it Be?

Many rashes can cause skin changes just like psoriasis. With careful inspection, it should be possible to differentiate these psoriasis posers from the real thing. Psoriasis is most likely to be confused with another rash based on its location. For example many things can cause a red scaly rash in the groin area other than psoriasis. Let's take a look at what else it could be (referred to as a "differential diagnosis" in medical lingo) of psoriasis based on the part of the body affected by a rash.

Scalp Rashes That Aren't Psoriasis

Doctor inspecting a baby with seborrheic dermatitis
Seborrheic dermatitis on baby's head can look like scalp psoriasis. delectus / Getty Images

If you have a rash on your scalp that looks like scalp psoriasis, what else could it be?

Scaly red rashes on the scalp can be caused by seborrheic dermatitis, also known as dandruff. The difference is that psoriasis of the scalp often has significant thickening of the skin and thick adherent scales.

Seborrheic dermatitis, in contrast, usually just has some pinkness of the skin of the scalp with much finer scales. Seborrheic dermatitis often involves the eyebrows and the sides of the nostrils as well, so sometimes, involvement of these areas will help to separate this disease from psoriasis.

Fungal infections of the scalp are not uncommon in children and so a child with a scaly scalp may have fungus, psoriasis or seborrheic dermatitis. Hairs can be plucked and examined under a microscope (a KOH test) to help confirm a diagnosis of fungus.

Tinea capitis, also known as "ringworm of the scalp," is a fairly common cause of scalp rashes in children between the ages of three and seven. It's important for parents to recognize that the infection is not caused by a worm, but rather a fungus.

If your rash is scalp psoriasis, the rash can vary from only a few spots of scaling, to an extensive red and scaly rash which covers your scalp and extends down to your forehead or neck. In severe scalp psoriasis, accompanying hair loss may occur. That said, and though it may take a few months to get your symptoms under control, there are several treatment options available for those who suffer with this condition.

Flexural Area Rashes that Aren't Psoriasis

The term "flexural areas" are used to describe the creases in tissue which occur in the armpits, the groin, and under the breasts. When these flexural areas become wet or stay wet, the increased moisture can lead to scaly rashes, often with a pasty white substance present. These findings are common with psoriasis but occur with other conditions as well.

Candidiasis is a condition caused by the yeast ​Candida albicans. Perhaps best known for its role in causing thrush and diaper rashes in babies and vaginal yeast infections in women, Candida often causes rashes in the armpits, the groin, and beneath the breasts which can appear very similar to psoriasis.

A "dryer" red rash with scales around the edges is typical of Tinea cruris or "Jock Itch." It is caused by the fungus Trichophyton rubrum which has a distinct appearance (almost like that of hair) under the microscope. It is often treated with topical antifungal agents, similar to the treatment of yeast infections.

A darker discolored patch in these areas without scaliness may be erythrasma, a minor bacterial infection caused by the bacteria Corynebacterium minutissimum. In addition to causing infections on the foot (often between the third and fourth toes), it may cause rashes in the groin, armpits, and beneath the breasts. It may be distinguished by its brown appearance. This condition, which is more common in those who are overweight or with diabetes, can often be treated with topical antibiotics.

To differentiate these rashes and conditions from psoriasis, your dermatologist has several options. Observing the skin scales under the microscope may reveal the cause, as may a KOH test. Examining the area with an ultraviolet light (a Wood's light) may also be helpful, as yeast glows a pale yellow with this procedure.

Hand and Foot Rashes that Aren't Psoriasis

Hand and foot rashes may be the most difficult to differentiate from true psoriasis.

Eczema, fungal infections, allergic reactions, and irritation from chemicals can all cause changes which may be confused with psoriasis. Most of these rashes cause thickening, redness and scales on the backs of the hands or feet but may cause a blistering rash on the palms and soles.

Nail changes with psoriasis are common, but can also occur in fungal infections or severe eczema involving the cuticle areas.

Diagnosis can be very difficult. Skin biopsies from hand and foot rashes can be confusing and often show mixed features in the same specimen. Differentiating hand and foot rashes from psoriasis requires significant skill and usually necessitates examination of other body parts to look for clues, such as the scalp, the elbows, and the knees. It's important to see a dermatologist who specializes in distinguishing these rashes if you have persistent problems, and in some cases, a second opinion may be needed.

Combination of Psoriasis and Other Skin Conditions on the Scalp, in Flexural Creases, and on the Hands and Feet

It's important that some of the other skin conditions mentioned here may occur at the same time as psoriasis. In fact, conditions such as Candida can go hand in hand with psoriasis. Candidiasis can stimulate secretion of the inflammatory chemicals (such as cytokines) which worsen psoriasis, and some of the medications used to treat psoriasis can predispose to infections with Candida.

Sources:

Armstrong, A., Bukhalo, M., and A. Blauvelt. A Clinician’s Guide to the Diagnosis and Treatment of Candidiasis in Patients with Psoriasis. American Journal of Clinical Dermatology. 2016. 17(4):329-36.

Kasper, Dennis L.., Anthony S. Fauci, and Stephen L.. Hauser. Harrison's Principles of Internal Medicine. New York: Mc Graw Hill education, 2015. Print.

Park, J., Park, Y., Kim, S. et al. Histopathological Differential Diagnosis of Psoriasis and Seborrheic Dermatitis of the Scalp. Annals of Dermatology. 2016. 28(4):427-32.

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