What is spongiotic dermatitis?
Spongiotic dermatitis is a term pathologists use to describe a pattern of injury in the skin caused by inflammation. It is called a “pattern of injury” because the changes seen are not specific to a single medical condition. The spongiotic dermatitis pattern of injury is most commonly seen in a group of medical conditions called eczema.
Your skin is the largest organ in your body. It is made up of three layers: epidermis, dermis, and subcutaneous fat. The surface, and the part you can see when you look at your skin, is called the epidermis. The cells that make up the epidermis include squamous cells, basal cells, melanocytes, Merkel cells, and cells of the immune system. The squamous cells in the epidermis produce a material called keratin, which makes our skin waterproof and strong and also protects us from toxins and injuries.
The dermis is directly below the epidermis. The dermis is separated from the epidermis by a thin layer of tissue called the basement membrane. The dermis contains blood vessels and nerves. Below the dermis is a layer of fat called subcutaneous adipose tissue.
Types of eczema
Doctors often divide eczema into different types based on the appearance of the rash, the area of the body affected, and the underlying cause. The list below describes the most common types of eczema:
- Atopic dermatitis: This common type of eczema most often affects children. Most patients with atopic dermatitis have a personal or family history of allergies or asthma.
- Irritant contact dermatitis: This type of eczema is caused by contact with water or chemicals that irritate the skin. Any area of the body may be involved. Treatment involves identifying and removing the trigger.
- Allergic contact dermatitis: This type of eczema is an allergic reaction that develops in the skin that has been exposed to a normally harmless chemical or substance. Common causes include nickel, hair dyes, and topical antibiotics.
- Lichen simplex: This type of eczema is caused by persistent rubbing or scratching of the skin. As a result, the skin appears thicker than normal.
- Nummular eczema (also known as discoid eczema): This type of eczema produces one or more round, well-defined, red patches. The exact cause of nummular eczema is unknown. However, in some patients the rash will develop following a scratch, insect bite, burn, or exposure to a chemical irritant.
- Seborrheic dermatitis: This type of eczema affects the scalp and face. It is caused by chemicals, which are produced by yeast, and live on the skin. Seborrheic dermatitis may occur in both infants and adults.
- Stasis dermatitis: This type of eczema typically affects the legs. It is caused by poor circulation and may often be seen in people who have varicose veins.
Other conditions associated with spongiotic dermatitis
- Fungal infections of the skin
- Drug/medication reactions
- Pityriasis rosea
- Gianotti-Crosti syndrome
How do pathologists make a diagnosis of spongiotic dermatitis?
Pathologists make the diagnosis after examining a small sample of skin removed in a procedure called a biopsy. The sample is examined under a microscope. The changes seen during this examination will depend on the condition causing spongiotic dermatitis as well as how long the injury has been present.
The type of spongiotic dermatitis described in your pathology report will help your doctor determine the cause. The changes seen in spongiotic dermatitis are commonly divided into three categories:
- Acute: In acute spongiotic dermatitis, fluid may be seen in the epidermis. The fluid pushes the squamous cells apart and gives the epidermis a sponge-like appearance which pathologists describe as spongiosis. Larger fluid-filled spaces may also develop. These are called vesicles. Specialized inflammatory cells, such as eosinophils and lymphocytes, may also be seen in the epidermis.
- Subacute: In subacute spongiotic dermatitis, fluid is seen in the epidermis although the amount is usually less than is seen in acute spongiotic dermatitis. The epidermis may be thicker than normal. Pathologists describe this change as acanthosis. An increased number of specialized inflammatory cells including eosinophils, lymphocytes, and plasma cells may be seen in the dermis.
- Chronic: In chronic spongiotic dermatitis there is usually very little fluid or inflammatory cells in the epidermis. In contrast, the epidermis is typically thicker than normal and the epidermis may form long projections that push down into the dermis. Pathologists describe this change as “psoriasiform” because a similar change can be seen in psoriasis.
by Bret Kenny and Allison Osmond MD FRCPC (updated August 18, 2021)