Background
Digital mucous cysts (DMCs) are benign ganglion cysts of the digits, typically located at the distal interphalangeal (DIP) joints or in the proximal nail fold. [1] Historically, little attention has been directed to the study of these cysts, despite their frequency. In the literature, DMCs have been referred to as cystomata, myxomatous cutaneous cysts, myxomatous degenerative cysts, periarticular fibromas, synovial lesions of the skin, periungual ganglions, mucous cysts, myxoid cysts, synovial cysts, dorsal cysts, nail cysts, cystic nodules, digital mucoid cysts, digital myxoid cysts, and digital mucinous pseudocysts.
DMCs usually occur on the hands, though they have also been noted on the toes. [2] (See Presentation.) The etiology of these cysts is uncertain but may involve mucoid degeneration. Often, these cysts are asymptomatic and do not require treatment. When treatment is indicated, medical therapies and surgical interventions of varying magnitudes may be attempted. (See Treatment.) Surgery may considered first-line therapy for DMCs, with sclerotherapy and cryotherapy as second-line options. [3] Recurrence after treatment is common. [4]
Pathophysiology
The mechanism by which DMCs form is unknown. It is believed that they arise from mucoid degeneration of connective tissue and that this process, in most cases, involves communication with the adjacent DIP joint and possible coexistence of osteoarthritis. Clinical and radiographic evidence of osteoarthritis is common at the site of the cysts, [5] and the frequent presence of osteophytes and spurring of the DIP joint were recognized in the 1970s. Active connection to the joint space may or may not exist, in that the mucoblasts associated with the cyst appear capable of sustaining the process.
Etiology
The causes of DMCs remain to be defined. Historically, a variety of etiologies, including a tuberculous process, have been suggested. It is believed that mucoid degeneration of connective tissue associated with proximal osteoarthritic changes is responsible for cyst formation. Trauma also may be a causative factor in some cases.
Epidemiology
United States and international statistics
Ganglions are the most common tumors or cysts of the hand, accounting for approximately 70% of the total, with DMC representing 10-15% of the total.
International frequency data are limited but have not been found to differ significantly from US statistics.
Age- and sex-related demographics
DMCs usually occur in the fifth to seventh decades, but they may be seen as early as the teenage years or among the elderly population. The mean age of onset is 60 years. One case report described a DMC in association with cutaneous mucinosis of infancy.
Women are affected more often than men (female-to-male ratio, 2-2.5:1).
Prognosis
DMCs have a good prognosis. Recurrence is common, except with radical surgery, which has significant associated morbidity. Most DMCs are asymptomatic and benign. Pain can result from the impingement of cysts on adjacent nerve fibers. Larger cysts can disfigure the affected digit. Nail deformities can occur.
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Digital mucous cyst proximal to nail unit.
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Digital mucous cyst at proximal nail fold.
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Histopathology of digital mucous cyst.
