Psoriasis is a common skin condition. It causes skin cells to grow and multiply faster than the body can shed them. As a result, the excess cells build up, causing plaques or lesions to form.

Plaque psoriasis is the most common form of psoriasis. It generally causes large, oval-shaped plaques to form on the skin. These can be a different color from the surrounding skin and appear scaly. They may appear on a person’s trunk, scalp, and buttocks, as well as other areas.

Ostraceous psoriasis is a rare subtype of plaque psoriasis. The plaques that form are hard and thick, sometimes resembling oyster shells.

Below, we explore ostraceous psoriasis in detail, including it symptoms, treatments, and outlook.

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In a person with ostraceous psoriasis, oyster shell-like plaques of skin tend to form on the scalp, trunk, buttocks, knees, or elbows.

Ostraceous psoriasis is linked with hyperkeratosis, the thickening of the outer layer of skin. The outer layer is made up of a protein called keratin. When hyperkeratosis occurs, the keratin in the outer layer starts to grow unchecked and thickens.

According to a 2020 study, ostraceous psoriasis has a strong link with psoriatic arthritis. Psoriatic arthritis is a type of inflammatory arthritis that affects about 1 in 4 people with psoriasis.

People with both conditions often need additional treatments for psoriatic arthritis.

The skin plaques that characterize ostraceous psoriasis are thick and hard.

The authors of a case report from 2015 described these plaques further. The inner faces of the plaques, they noted, tend to be concave, surrounded by a ring of thickened kin, and covered with thick scales that remain attached to the plaque. These authors, too, described the plaques as resembling oyster shells.

Other types of plaque psoriasis tend to cause inflamed, scaly lesions.

The plaques typically appear symmetrically, usually on the:

  • torso
  • knees
  • scalp
  • elbows
  • buttocks

Plaque psoriasis can also affect the nails, causing them to be pitted or discolored. The nails may start to separate from the nail beds.

If a person also develops psoriatic arthritis, certain joints may stiffen, swell, and become painful, and the symptoms may be worse in the morning. More specifically, the toes and fingers may develop sausage-like swelling. This is sometimes the first sign of psoriasis.

It may be worth noting that children can also develop psoriasis and psoriatic arthritis.

Anyone who thinks that they may have psoriasis should contact a healthcare professional. They may refer the person to a dermatologist, a skin condition specialist, who has more experience with psoriasis.

During an evaluation, a dermatologist tends to examine the person’s scalp, nails, and skin. They also generally ask about:

  • a family history of the disease
  • joint pain or involvement
  • recent changes in stress or illnesses
  • additional symptoms, including pain and itchiness

The dermatologist may also remove a piece of skin in the affected area. Examining this sample under a microscope can help confirm a psoriasis diagnosis.

Treating most cases of psoriasis involves reducing the severity of skin lesions and preventing them from flaring or spreading.

Ostraceous psoriasis treatment is similar to that of more common types of plaque psoriasis. According to one study, effective treatment can involve taking the immunosuppressive drug cyclosporine and using a topical product that contains both a steroid and an emollient, which softens the skin.

A dermatologist may also recommend:

  • phototherapy
  • oral medications
  • biologic drugs, which target the immune system
  • medicated creams, ointments, and other topical products designed to reduce psoriasis symptoms

Some oral medications for psoriasis include:

In addition, they may recommend strategies to ease symptoms and reduce the likelihood of psoriasis flares. These self-care techniques may include:

In addition, research indicates that the balance of bacteria and other microbes in the gut may play a role in psoriasis. The dermatologist may recommend taking a probiotic supplement.

Learn more about the relationship between gut bacteria and psoriasis here.

Psoriasis is a chronic condition with no cure, but treatment and self-care strategies can help reduce the symptoms and prevent them from flaring up. This can lead to clear or nearly clear skin.

Because ostraceous psoriasis is a rare subtype, specific information is limited. However, some research suggests that the medications and therapies that dermatologists typically prescribe for people with plaque psoriasis can benefit people with this subtype.

People with psoriasis have an increased risk of cardiovascular disease, and a doctor may recommend yearly monitoring. This may involve a cholesterol profile and an electrocardiogram, which records the heart’s electrical signals.

Ostraceous psoriasis is a rare subtype of plaque psoriasis. Although the plaques have a slightly different appearance from typical psoriasis plaques, and may resemble oyster shells, the diagnosis and treatments are similar.

A dermatologist will work with a person to determine the best approach to treatment, which can reduce the symptoms and help prevent them from flaring up again.