Mucoid cysts - also known as digital myxoid cysts - are benign lumps which develop on the toes or fingers, usually near a nail. They are painful and can be susceptible to recurrent infections. They can rub in footwear. They are often linked with osteoarthritis, as it is estimated that more than half of people with osteoarthritis also have mucoid cysts. Although anyone can develop mucoid cysts, they usually occur in those aged between 40 and 70. Women are twice as likely to develop mucoid cysts.
While there is no known direct cause of mucoid cysts, they are linked to the degeneration of synovial tissue around the toe joint or finger, which characterises degenerative joint diseases including osteoarthritis. Mucoid cysts can involve a small bony growth from the joint cartilage which is degenerating.
Aside from degenerative joint diseases, there is also a link to the high production of mucin in the fibroblast cells. And in younger people, a cyst could be caused by trauma to the toe or finger.
Mucoid cysts usually develop on the dominant hand, near the nail on either the index or middle finger. Toe cysts are not as common.
The main symptom of mucoid cysts is an oval or round bump which is small in size - usually up to 1cm. They are typically either filled with fluid or firm, are smooth, and can be painful or become infected. They can be skin coloured, with a blue or red tinge which can appear similar to a pearl. Mucoid cysts usually grow slowly. A joint nearby to the location of the mucoid cyst may be the site of arthritis pain.
In some cases, cysts which grow over the nail can cause it to split, potentially leading to the complete loss of the nail.
Among the non-surgical treatment options for mucoid cysts are cryotherapy, which drains the cyst before liquid nitrogen is used to freeze and thaw it, but has a relatively high recurrence rate; infrared coagulation, which burns away the cyst from the base; intralesional photodynamic therapy, which drains the cyst and injects a substance which turns it more light-sensitive, before it is burnt away with a laser light; repeated needling, using a knife blade or sterile needle to puncture and drain the cyst, and repeating the procedure; and carbon dioxide laser, burning off the cyst base after it is drained. The cyst can be padded so it doesn’t rub in footwear and become infected.
The most common surgical treatment for mucoid cysts is a procedure which carefully removes the cyst right from its source before covering it with a skin flap. The flap is designed to close as the area heals. A dye injection can be used to allow the fluid leakage source to be pinpointed.
Recurrence rates with non surgical treatments are high but even with surgical removal there is always a small chance of the cyst recurring.
As with all foot surgery it is normal for swelling to persist for some months after surgery and is completely normal. This swelling will eventually completely subside with time and can take up to 12 months but often goes well before this.