Plaque psoriasis — also known as psoriasis vulgaris — is an inflammatory skin condition that causes lesions, or plaques, to form on the skin. It’s the most common type of psoriasis, and there are a few different kinds. One rare type of plaque psoriasis is rupioid psoriasis, which causes the formation of thick, cone-shaped lesions.

Because rupioid psoriasis is so rare, doctors and researchers are still learning about it. Small case studies have reported on symptoms and potential treatments, but larger studies are needed to confirm these findings. In this article, we’ll discuss what is known about rupioid psoriasis and how it’s diagnosed and treated.

What Is Rupioid Psoriasis?

Rupioid psoriasis lesions typically contain keratin, an essential protein found in the skin. Many doctors describe these lesions as looking like limpets, or cone-shaped shells found in the ocean. Because of its appearance, rupioid psoriasis has also been nicknamed “coral reef” psoriasis.

The skin lesions seen in rupioid psoriasis are different from those found in a typical case of plaque psoriasis. Many people with plaque psoriasis have dry, scaly patches covered in dead skin cells. The color of the scales depends on your skin tone. People with lighter skin tones may have white, silvery, or red patches, and those with darker skin tones have patches that may be gray, brown, or purple.

Who Develops Rupioid Psoriasis?

Rupioid psoriasis is rare, so not much is known about how many people it affects. Some doctors have noted in case reports that it seems to occur in people with other health conditions that affect the immune system. For example, rupioid psoriasis has been reported in people who have HIV. People with HIV are more likely to have more severe psoriasis in general, even though their immune system is suppressed.

Doctors also believe rupioid psoriasis may affect more people with psoriatic arthritis (PsA). This observation was seen in some case reports — however, more studies are needed to confirm the association. It’s estimated that around 30 percent of people living with psoriasis also develop PsA. Along with developing skin lesions, people with PsA have stiff, tender, swollen joints, which can affect their mobility. Other symptoms include eye pain and redness — known as uveitis — and nail changes.

Symptoms of Rupioid Psoriasis

The main symptom of rupioid psoriasis is round lesions that look like limpet shells. They typically look like dark-colored cone shapes sticking out from the skin. The lesions tend to be small, between three-fourths of an inch and 2 inches (2 centimeters and 5 centimeters) across. There is a clear distinction between the skin and the lesion itself.

Plaque psoriasis can affect almost any area of skin, but the most common locations include the torso or lower back, scalp, knees, and elbows. Skin lesions are usually symmetrical, meaning they’re found in the same location on both sides of the body. Rupioid psoriasis is also known to affect the arms and legs.

Another sign of plaque psoriasis is known as the Auspitz sign. This term refers to the small pinpricks of bleeding that appear when a plaque is removed. This is due to the presence of small, dilated blood vessels.

Rupioid psoriasis may look similar to another type of psoriasis known as ostraceous psoriasis. Lesions in ostraceous psoriasis tend to have centers that cave inward and look similar to oyster shells.

Diagnosing Rupioid Psoriasis

To diagnose rupioid psoriasis, your doctor or dermatologist will perform a physical exam and a few tests to rule out other conditions. Your doctor will create a differential diagnosis, which is a list of all the potential conditions your symptoms may be related to. The lesions seen in rupioid psoriasis can look similar to other skin conditions, such as:

• Secondary syphilis — A bumpy skin rash that develops a few months after syphilis infection and has sores that look similar to warts
• Histoplasmosis — A fungal infection that causes the formation of skin lesions or plaques
• Crusted scabies — A severe skin infestation with mites that causes thick crusts to form over the skin, typically seen in people with weak immune systems and older individuals

During a physical exam, your doctor will take a close look at your skin, noting where you have lesions and what they look like. The telltale sign of rupioid psoriasis is cone-shaped, dark lesions. If your doctor decides to remove one, you may see the Auspitz sign afterward.

Your doctor may also perform a skin biopsy. This test takes a small piece of your skin tissue from a lesion to look at under a microscope. The most common type of biopsy for psoriasis is a punch biopsy, which uses a pencil-like device to “punch” out a round piece of a lesion to look at the deeper layers of skin. Your doctor will then close the hole with a few stitches.

A pathologist (a doctor who specializes in reading biopsies) will use the skin sample to look for any signs of keratin buildup associated with rupioid psoriasis. The biopsy can be used to rule out other conditions, such as a fungal infection or mite infestation.

Blood tests also rule out other conditions, including syphilis. Your doctor may take a small blood sample to test for antibodies that your immune system makes in response to infection. If your blood test result is positive, your skin symptoms are likely caused by a syphilis infection.

Treatments for Rupioid Psoriasis

Rupioid psoriasis is a chronic (ongoing) skin condition that currently has no cure. However, there are several plaque psoriasis treatments available to help clear your skin and better manage the disease. Depending on where your rupioid psoriasis is located and how severe it is, your doctor or dermatologist may recommend treatment with topical or systemic therapy.

Topical Treatments

Topical treatments are applied only to the areas of skin with lesions. They don’t have as many side effects as bodywide (systemic) treatments. Commonly prescribed topical treatments for plaque psoriasis include:

• Steroid creams — Corticosteroids help relieve itching and inflammation.
• Calcineurin inhibitors, such as pimecrolimus (Elidel) and tacrolimus (Protopic)
• Newer nonsteroidal creams, such as tapinarof cream or roflumilast cream

Your doctor or dermatologist may recommend using a gentle moisturizer to keep your skin hydrated. Moisturizers that contain salicylic acid or urea help thin out lesions. Although extra lotions or creams can’t replace your rupioid psoriasis treatment prescribed by your doctor, they can help control some symptoms.

Systemic Treatments

Systemic treatments for plaque psoriasis work throughout your entire body to reduce inflammation and relieve skin symptoms. They may be given as pills or tablets taken by mouth, or they may be injected or infused into the bloodstream. According to the National Psoriasis Foundation, systemic therapies are used to treat psoriasis in people who haven’t responded to phototherapy or topical treatments.

Because rupioid psoriasis is so rare, there aren’t many studies on which systemic treatments work best. Your doctor or dermatologist may prescribe a common plaque psoriasis treatment, such as:

• Methotrexate — An immunomodulator that reduces the activity of the immune system and may help slow cell growth to prevent skin lesions (This medicine can harm the liver, so your doctor will order follow-up blood tests.)
• Acitretin (Soriatane) — A synthetic retinoid drug made from vitamin A that slows cell growth
• Cyclosporine — A disease-modifying antirheumatic drug (DMARD) that controls inflammation (Cyclosporine can affect the kidneys.)

Biologics are antibodies created in a lab that stop certain parts of the immune system from causing inflammation. Several biologics are approved by the U.S. Food and Drug Administration (FDA) for treating plaque psoriasis, including:

• Adalimumab (Humira)
• Ustekinumab (Stelara)
• Infliximab (Remicade)
• Etanercept (Enbrel)
• Guselkumab (Tremfya)
• Risankizumab-rzaa (Skyrizi)

If you have rupioid psoriasis and PsA, your doctor may prescribe a biologic that’s approved for treating both conditions.

The effectiveness of these treatments can vary from person to person. It may take trial and error to find the right combination of medications and therapies that work for you. If you think you may have rupioid psoriasis, ask your dermatologist for an accurate diagnosis and treatment plan.

Talk With Others Who Understand

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