Cutaneous Mucinosis in Dogs

The main symptom of mucinosis is the accumulation of mucin in the skin, leading to severe skin folding and vesicles, or bumps filled with the excessive mucin. Hyaluronic acid (HA) is the main component of mucin. HA is a carbohydrate that occurs naturally in the body to bind water and help to lubricate the body’s movable parts, such as the joints. When the levels of HA become higher than normal, more mucin is produced, and is pushed to the upper skin layer creating vesicles. Mucinosis is believed to be the result of a genetic defect, most probably relating to the metabolism of hyaluronic acid. 

Mucinosis is most often seen on the neck, shoulder area, hocks, forelimbs, and around the anus. It can be concurrent, or even caused by, hypothyroidism. Breathing issues can occur if vesicles form in the back of the mouth, causing snorting or snoring. Secondary diseases have been associated with severe mucinosis, and can include intertrigo, or skin fold inflammation, bacterial infections, and entropion, or the condition when the eyelid is inverted or folded inward.

Cutaneous mucinosis, also known as idiopathic mucinosis, primarily affects Chinese Shar Peis, and is common to the breed. A higher than normal build-up of mucin occurs just under the skin in this breed, thickening the skin and giving Shar Peis their characteristic excessive skin folds. Mucinosis occurs when this thick, clear, jelly-like fluid is produced in higher than normal amounts, forming vesicles that can rupture. While they usually don’t cause severe problems for the affected dog, they can create skin issues, breathing issues, and other secondary conditions that can lead to serious deterioration.

While often outgrown around 5 years of age, symptoms of mucinosis often vary in severity. They include:

• Thickened skin
• Excessive skin folding
• Lumps or bumps (vesicles) filled with mucin
• Scabs from ruptured vesicles
• Breathing issues
• Snoring
• Snorting
• Thinning hair
• Hair loss
• Intertrigo, or skin fold inflammation 
• Bacterial skin infections 
• Eyelid that is inverted or folded inward, referred to as entropion

Hypothyroidism is a related condition, and symptoms of this disease include:

• Mental dullness
• Lethargy
• Intolerance to exercise
• Weight gain without increased appetite

The cause of cutaneous mucinosis is believed to be an inherited genetic mutation of the Shar Pei breed. One theory suggests that the mucinosis may be due to a higher amount or increased activity of hyaluronic acid, while another theory targets a defect in the metabolism of the carbohydrate. These conditions directly relate to an overabundance of the HA which causes the associated symptoms.

Your veterinarian will look at any symptoms present and the results of testing to determine if a diagnosis of cutaneous mucinosis is appropriate. A skin biopsy can assess if there is an excessive amount of mucin in the layers of skin, while microscopic examination with a special staining can identify the contents of the mucin. In general, your veterinarian will determine if there is a higher level of hyaluronic acid present, which leads to a positive diagnosis.

Hypothyroidism is a condition that presents similar symptoms, and can even lead to severe mucinosis. Because of this, your veterinarian may test for this condition. Tests for hypothyroidism include measuring levels of thyroid hormones in a blood sample, an ultrasound or scintigraphy to check the thyroid gland, a TSH stimulation test, urinalysis, and responses to thyroid supplementation.

Since this is such a common condition in the breed that generally does not affect the health of the dog, treatment is usually not necessary. However, if your dog is presenting breathing problems or a severe case of mucinosis, then treatment with corticosteroids may be considered in gradually tapering doses over many weeks. This can reduce the amounts of mucin, but can also cause padding loss in your dog’s muzzle. While this side effect will normally correct itself in time, the muzzle may not regain its original appearance. Also, the mucinosis can reappear, even with medication therapy. If repeated treatment is required, hypothyroidism is ruled out.

If hypothyroidism is present, your veterinarian will treat that as well, usually with thyroid hormone supplementation. Allergies can make mucinosis worse, and will be treated also if necessary. Be aware that risks associated with anesthesia are increased with this disease, such as respiratory arrest.

Recovery is good, as your dog may outgrow the condition. Even with treatment, mucinosis can reappear. In most cases, this condition will not affect your dog’s day to day life, or change its lifespan, and generally remains cosmetic only.