Psoriasiform dermatitis

by Jason Wasserman MD PhD FRCPC and Stephanie Petkiewicz MD PhD FRCPC
November 14, 2024

Psoriasiform dermatitis is a term for a reactive pattern of skin changes that can result from several different underlying conditions. It is called psoriasiform because the changes resemble those seen in psoriasis.

What are the symptoms of psoriasiform dermatitis?

People with psoriasiform dermatitis often notice red patches of skin with a dry or flaky surface (referred to as scaly plaques). These plaques may vary in size and can appear on areas like the elbows, knees, scalp, and sometimes on other parts of the body.

Common symptoms include:

• Red plaque on the skin.
• Scaly or flaky skin on the affected areas.
• Itchiness that may vary in intensity.
• Discomfort or soreness if the skin becomes irritated.

The symptoms can be similar to psoriasis, so a detailed examination and sometimes a biopsy (a sample of skin tissue) are needed to tell them apart.

What causes psoriasiform dermatitis?

Psoriasiform dermatitis can have several causes, as it describes a reactive pattern of skin changes rather than a single disease.

Some common causes include:

• Psoriasis: Psoriasis itself is a primary cause of this pattern and involves an overactive immune response that leads to increased skin cell production and inflammation.
• Allergic reactions: Certain products, like soaps, cosmetics, or metals, can trigger an allergic response in the skin, causing psoriasiform changes.
• Infections: Some infections can lead to skin inflammation and mimic the pattern seen in psoriasiform dermatitis.
• Autoimmune responses: Other autoimmune conditions can cause similar patterns of skin injury as the body’s immune system mistakenly targets skin cells.
• Medications: Certain medications can cause skin reactions as a side effect, leading to a psoriasiform pattern.
• Chronic rubbing/irritation of the skin:  The skin responds by becoming thicker.

Each of these causes may lead to similar changes in the skin, so it is important to identify the underlying cause for treatment.

How is this diagnosis made?

Psoriasiform dermatitis describes changes seen when the skin is examined under a microscope. For this reason, the diagnosis can only be made after a biopsy, where a pathologist examines a small sample of the affected skin. By studying the tissue under the microscope, the pathologist can identify the specific features of psoriasiform dermatitis and help rule out other similar skin conditions.

What are the microscopic features of psoriasiform dermatitis?

Under the microscope, psoriasiform dermatitis shows a distinct pattern that pathologists use specific terms to describe.

These features include:

• Thickening of the skin layers: Pathologists call this acanthosis or acanthotic change, where the epidermis (outer skin layer) becomes thicker due to increased skin cells.
• Elongation of the rete ridges: In psoriasiform dermatitis, the rete ridges, projections of the epidermis that extend into the deeper layers of the skin, become longer. This change is described as elongated rete ridges.
• Presence of inflammatory cells: Inflammation in the epidermis and dermis (the skin layer beneath the epidermis) is a common feature. Pathologists might note an inflammatory infiltrate consisting of neutrophils, lymphocytes, and other immune cells.
• Scales on the surface: The accumulation of layers of dead skin cells on the surface is referred to as hyperkeratosis. When these layers contain retained nuclei, it is called parakeratosis.

What is the treatment for psoriasiform dermatitis?

The treatment for psoriasiform dermatitis depends on the cause and the severity of the symptoms.

Common treatments include:

• Topical corticosteroids are creams or ointments that reduce inflammation and relieve itching.
• Moisturizers to keep the skin hydrated and prevent further irritation.
• Antibiotics if an infection is present or suspected.
• Avoiding triggers, such as specific products or materials, if an allergy is involved.

Treating the underlying condition that causes psoriasiform dermatitis can help manage the skin symptoms. If symptoms don’t improve or if the condition worsens, it’s important to follow up with your healthcare provider.