If a person finds that their psoriasis treatment is not working, they may want to ask for a second opinion or further diagnostic tests. Other checks can include a skin biopsy to ensure the person has psoriasis rather than something else.
This article looks at the different types of psoriasis and other conditions with similar symptoms.
Is it psoriasis or something else?
It may be difficult to tell psoriasis apart from other skin conditions.
Doctors class psoriasis and other conditions that have similar effects on the skin in a group they refer to as psoriasiform dermatitis.
Even so, it can still be difficult for a dermatologist, who is a specialist skin doctor, to tell some of them apart.
We discuss some of these conditions in more detail below and explain how they differ from psoriasis.
Different types of psoriasis
There are five main types of psoriasis, with a range of different symptoms:
- Plaque psoriasis: Showing patches of thick, scaly, silvery plaques on the skin. Around 80 percent of people with psoriasis have plaque psoriasis.
- Guttate psoriasis: A large-scale rash consisting of small, reddish bumps.
- Inverse psoriasis: Dry, red, scaly patches of skin in the skin folds, such as the armpits and genitals. Inverse psoriasis causes thinner scales than plaque psoriasis.
- Pustular psoriasis: In this type, pus-filled blisters form on a person's skin.
- Erythrodermic psoriasis: An aggressive form of psoriasis that causes widespread skin peeling, intense burning, fever, and inflammation.
Plaque psoriasis causes the skin cells to multiply faster than usual. Symmetric, clear areas of inflamed skin with flaking, slivery white scaly plaques that may itch characterize it. These patches usually develop on the outer elbows and knees, lower back, hands, and scalp.
People with psoriasis may notice the Koebner phenomenon, where areas of psoriasis develop in places where a skin injury has occurred.
They will usually discuss a person's medical history, as well, which can often be the same for psoriasis and eczema.
However, a dermatologist can typically distinguish between eczema and plaque psoriasis by looking at the specific symptoms and their location.
Eczema is more likely than psoriasis to affect the insides of the arms and knees. Psoriasis often occurs on the outside of the elbows and knees, lower back, and scalp.
Compared with eczema, psoriasis will tend to affect more well-defined areas of skin.
Seborrheic dermatitis is a form of eczema that often affects the scalp. It causes rough, scaly skin to develop on the face and scalp.
Seborrheic dermatitis can cause similar symptoms as scalp psoriasis, such as:
- flaking skin on the scalp
- patches of itchy skin that can be inflamed
- areas of skin redness
While psoriasis tends to cause thick scales to develop, seborrheic dermatitis produces thinner, slightly greasy-looking skin flakes.
Pityriasis rubra pilaris
Pityriasis rubra pilaris refers to a group of skin conditions that cause inflammation and scaling.
Similarly to plaque psoriasis, symptoms of pityriasis rubra pilaris develop on the palms of the hands, the scalp, and the soles of the feet. People may also notice their nails become thickened and discolored.
A dermatologist can often tell these conditions apart by using dermoscopy. This procedure involves looking closely at the skin with a specialized handheld microscope without the need for a skin biopsy.
A fungus causes ringworm and not a worm. Ringworm and psoriasis both cause red, scaly patches of skin. These patches are more circular and uniform when ringworm rather than psoriasis is the cause.
Jock itch tends to affect areas of the body where sweat accumulates.
Jock itch is a fungal infection originating from the fungus tinea cruris. This fungal organism causes a scaly rash in places where the skin folds and sweat accumulates.
The areas that jock itch favors include the groin, armpits, and genitals. These are the same spots that inverse psoriasis affects.
Smooth, red, shiny patches on folds of the skin, such as at the back of a person's knee, under the arm or around the groin characterize inverse psoriasis, however.
Tinea versicolor is a fungal infection that causes small, red, sometimes scaly marks on the skin. People may confuse tinea versicolor with guttate psoriasis, which produces similar small red marks.
Tinea versicolor can also cause patches of light and dark skin, and people can confuse it with vitiligo.
Both pityriasis rosea and plaque psoriasis cause patches of scaly rash on the skin. Pityriasis rosea is characterized by one large, scaly patch, that doctors refer to as the mother patch, and smaller patches they call daughter patches.
Lupus and psoriasis are both autoimmune conditions. Both cause skin rashes, though lupus also affects the internal organs. Lupus is also less common and more severe than psoriasis.
People may confuse lupus with psoriatic arthritis, as both conditions can cause joint pain. Psoriatic arthritis is a type of arthritis.
It is not common for a doctor to misdiagnose skin cancer and psoriasis. If a doctor suspects skin cancer, they will order diagnostic tests to find out more.
Some types of skin cancer, such as basal cell carcinoma and squamous cell carcinoma, can cause scaly, rough, or raised areas of skin that may itch.
It is unlikely that a person would mistake melanoma for psoriasis as the symptoms are different.
Other psoriasis mimics
Secondary syphilis can resemble plaque psoriasis, but it also causes fever and swollen lymph nodes.
Depending on the specific symptoms, people can receive a misdiagnosis of different types of psoriasis.
People might confuse plaque psoriasis as one of the following conditions:
- Lichenified dermatitis, where a person's skin becomes leathery.
- Secondary syphilis, which includes a skin rash plus swollen lymph nodes and fever.
- Mycosis fungoides, a rare type of skin cancer.
- Inflammatory linear verrucous epidermal nevus, a genetic skin condition.
Inverse psoriasis can also mimic:
- Intertriginous cutaneous candidiasis.
- Dermatophytosis, a fungal infection.
- Keratosis follicularis, a genetic disorder that causes papules around the scalp, forehead, and upper chest.
- Benign familial chronic pemphigus, a genetic disorder that causes blistering.
Pustular psoriasis is distinctive by its white blisters on a person's skin, most commonly found on their hands or feet.
People could confuse this form of psoriasis with a variety of systemic infections, or with a disease that causes similar white blisters. One such disease is acute generalized exanthematous pustulosis.
Erythrodermic psoriasis is a severe form of psoriasis, showing widespread areas of red, very sore, itchy skin. It can mimic other inflammatory skin conditions that cause widespread redness of a person's skin, a symptom known as erythema.
Who does psoriasis affect?
Psoriasis affects men and women equally. It often develops between the ages of 15 and 35 years, but it can develop at any age. In rare cases, it can affect infants.
Psoriasis is more common in Caucasians compared with African-Americans. People with a family member who has psoriasis are also more likely to get it.
Tips for getting the right diagnosis
For the best chance of getting the right diagnosis, a person should make sure they give an accurate history when a doctor or dermatologist asks. The more information a medical professional has to work with, the more likely they are to diagnose a person's illness correctly.
This is especially important with skin conditions such as psoriasis. A medical professional will typically rely on both a history and a visual assessment to work out what a person's skin condition is. A visual assessment alone may not be enough.
If a person is unsure about their diagnosis, they can request further diagnostic tests. This may involve speaking to a dermatologist, who might use dermoscopy or recommend a skin biopsy.
A skin biopsy involves taking a small sample of the skin and sending it to a lab for testing.
If a person's treatment is not working, or if their symptoms are getting worse, they may have received a misdiagnosis of psoriasis.
Otherwise, they may not yet have found the most effective treatment that works for them. Different people may respond differently to the range of possible psoriasis treatments.
People can speak to their doctor or dermatologist about their concerns regarding a psoriasis diagnosis or misdiagnosis.