Mucin is a sticky glue-like substance produced by cells called fibroblasts. Mucin is what makes Shar-Pei skin wrinkle and gives them padding on their muzzles and hocks. It is normal for Shar-Pei. Sometimes excessive mucin bubbles up in the skin, forming vesicles. This is called cutaneous mucinosis. These vesicles can be fragile and spontaneously break if the condition is severe or the bubbles of mucin may rupture during rough play, etc., causing the sticky substance to ooze out. It is normally not a problem for the dog. If it is excessive, e.g. causing much spontaneous rupture followed by healing scabby areas or if the skin is tearing frequently, the production of mucin can be shut down by low dosages of prednisone or other corticosteroids. Usually very low doses of alternate day prednisone result in dramatic improvement. If it is not bothering the dog, I would not treat it because corticosteroids are not without risk. Sometimes Shar-Pei will “lose” their muzzles because of steroids administered medically or because they are stressed by fever or illness and their own body’s production of cortisol by the adrenal glands will cause the mucin to “shrink”. Usually, they will return to normal with time but sometimes they never regain their old appearance.
Swollen hock syndrome is a term for the hock swelling that accompanies the high fever of Shar-Pei fever. It results in pain, lameness and only lasts a few days. If there is no fever, it is not swollen hock syndrome. Mucinosis frequently occurs on the neck, forelimbs, shoulder area, hocks and about the anus.
Allergies can make mucinosis worse and I frequently see flare-ups in dogs with allergic dermatitis coinciding with their itchy skin disease.
This is a picture of Shar-Pei skin with cutaneous mucinosis: