Digital Mucous Cyst

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. They usually occur on the hands, although they have also been noted on the toes. 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. Recurrence is common.[1, 2, 3]

Historically, little attention has been directed at studying these cysts despite their frequency. In the literature, they 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.

Hippocrates first appreciated ganglion cysts, describing a knot of tissue full of fluid. In 1746, Eller concluded that ganglia formed from the herniation of the synovial lining of a joint. In 1882, Hyde first described the digital mucous cyst. In 1893, Ledderhose suggested that ganglia arose spontaneously in the subcutaneous tissue. In 1895, Ritschel proposed the earliest formulation of the theory that mucoid degeneration may be responsible for digital mucous cysts; Carp and Stout popularized the theory in 1928. Then, in 1947, Anderson reported that cysts caused the nail deformities.

The mechanism of formation of digital mucous cysts is unknown. Currently, it is believed that the cysts 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,[4] 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, as the mucoblasts associated with the cyst appear capable of sustaining the process.

The causes of digital mucous cysts remain unclear. Historically, a variety of etiologies, including a tuberculous process, have been suggested. At present, 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.

Frequency

United States

Ganglia are the most common tumor or cyst of the hand. They account for approximately 70% of all such tumors or cysts, with digital mucous cysts comprising 10-15% of the total.

International

Frequency data are limited but not significantly different from US statistics.

Sex

Women are affected more often than men (female-to-male ratio of 2-2.5:1).

Age

Digital mucous cysts usually occur in the fifth to seventh decades, yet they may be seen as early as the teenage years or among the elderly population. The mean age of onset is 60 years. One report describes a case in association with cutaneous mucinosis of infancy.

Digital mucous cysts have a good prognosis. Recurrence is common except with radical surgery, which has significant associated morbidity. Digital mucous cysts most often 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.

Typically, the cysts are asymptomatic. They may appear suddenly or develop over a period of months. Grooving of the nail may precede the clinical manifestation of the cyst itself by up to 6 months. Often, osteoarthritis of the small joints is noted at the site of cyst emergence. Intermittent spontaneous discharge of cyst contents can occur, and, in a significant fraction of cases, cysts may disappear spontaneously.

Antecedent trauma has been documented in a small minority of cases. As cysts enlarge, pain is an increasingly common complaint. Patients are also likely to complain about the appearance of larger cysts and may report interference with function.

Pertinent physical findings are limited to the skin, joints, and nail unit. Note the images below.

Digital mucous cysts are usually solitary, round-to-oval, dome-shaped, firm-to-fluctuant papulonodules from 1-10 mm in diameter that have overlying skin that ranges from very thin to moderately thick. The cysts contain a viscous, gelatinous fluid that may be clear or yellow-tinged. Some cysts are verrucose. Pain is associated with relatively larger cysts.

The cysts are located off the midline of the digits and, according to one series, are more common on the radial than ulnar aspect of the fingers. They most often are found on the dorsolateral aspect of the fingers, intradermally, between the DIP joint and proximal nail fold.[5] Less frequently, they occur between the proximal nail fold and the nail plate, beneath the nail matrix, or in the pulp of the digit. Cysts most frequently are found on the middle or index finger of the dominant hand; toe involvement is less common.[6] Cysts located under the nail plate (subungual cysts) have common features that have been characterized in one series. In most cases, the lunula is discolored (most often red, less often blue) and transverse curvature of the nail is almost always increased, frequently resulting in lateral ingrowth

Digital mucous cysts are translucent to flesh-colored. One case report described a herpetiform appearance.[7] Lesions may be solitary or present as multiple nodules.[8] When they are under the nail matrix, a red lunula and a longitudinal brownish band may be seen.

Longitudinal grooving or depression of the nail occurs when digital mucous cysts involve the posterior nail fold. Grooving may be accompanied by transverse ridging and thinning of the nail overlying the cyst. Gross disruption of the nail is less common. Digital mucous cysts are more likely to be above than below the nail matrix.

A consensus has emerged that digital mucous cysts are frequently, if not always, located at osteoarthritic joints.

Plain radiography findings are not diagnostic for digital mucous cysts (DMCs) but will demonstrate a nonspecific soft-tissue density and adjacent bony involvement consistent with osteoarthritic changes.

Ultrasonography evaluation reveals a rounded or lobulated mass of markedly hypoechoic appearance with smooth, well-defined walls immediately adjacent to the involved synovial compartment. A tapering margin, which constitutes the "neck" of the cyst, is observed. Ultrasound is faster and better tolerated than MRI, but MRI is less operator dependent.

CT scanning usually demonstrates a well-defined water density mass with normal surrounding soft tissue.

On MRIs, homogenous low-intensity lesions are seen on T1-weighted images, with markedly increased signal and sharp borders on T2-weighted images. Other cyst features that may be observed are intracystic septa, satellite cysts, cyst pedicles, osteoarthritis of the distal interphalangeal (DIP) joint, subungual cysts, and multiple flattened cysts. MRI is an excellent modality for visualizing soft tissue cyst structures and may be particularly useful preoperatively.[9]

Transillumination with a penlight may assist in making the diagnosis and in differentiating digital mucous cysts from giant-cell tendon sheath tumor.

Approximately 12 hours before surgery, the DIP joint may be injected with methylene blue and local anesthetic. The coloring of the entire cyst and pedicle at the time of surgery may facilitate removal of the entire cyst and minimize the risk of recurrence.

Injection of radio-opaque contrast material into the cyst and passage of this material into the adjacent joint may yield a radiograph that reveals the entire extent of the cyst. This technique provides an image of the cyst extent prior to the surgery itself; therefore, it may be more practical than methylene blue infusion.[10]

Chemical analysis of matrix is a research test that has no role in routine diagnosis. Cellulose acetate paper electrophoresis and enzymatic digestion liquid chromatography demonstrates that digital mucous cysts contain copious quantities of glycosaminoglycans, primarily hyaluronic acid.

Fine needle aspiration may have an ancillary role in diagnosis. On such aspiration, a large amount of clear gelatinous fluid is expressed. Rare macrophages and histiocytes are found in the thick, mucoid matrix, as are a few tight clusters of cells, some collagen fibers, and red blood cells with altered shapes.[11]

On microscopy, a pseudocyst with a fibrous capsule and myxomatous stroma with scattered fibroblasts is seen. A partial mesothelial lining, but not a true cyst wall, may be found. The overlying surface epithelium demonstrates compact hyperkeratosis with a collarette of hyperplastic epidermis. The mucinous contents stain basophilic with hematoxylin and eosin and can be seen clearly when stained for acid mucopolysaccharides with colloidal iron or Alcian blue. Note the image below.

On scanning electron microscopy, a porous network of collagenous fibers form the cyst wall and a fibrillated inner surface composed of a random arrangement of collagen fibers is observed. An intermittent thin membrane occurs on the inner surface, but no evidence of a cellular lining is apparent.

Medical care for digital mucous cysts (DMCs) includes the following:

• Soaks

• Local heat

• Massage

• Occlusive treatment with topical steroids and Cordran tape

• Intralesional corticosteroids

• Home remedies - Salves, poultices, and plasters

• Application of heparin cream

• Silver nitrate

• Chemical cauterization with phenol

• Sclerotherapy with polidocanol[12]

• Digital compression, if the cyst is soft and located over a bony prominence

• Striking with a large book (potential for unintended trauma)

• X-ray therapy and radium irradiation (of historical interest only)

In a study of about 100 patients, surgery yielded the highest cure rate (95%) compared with sclerotherapy (77%), cryotherapy (72%), corticosteroid injection (61%), and expression of cyst contents (39%) (P< .001).[13]

The most conservative surgical intervention entails multiple episodes of needling the cyst with a wide-bore needle until resolution is achieved. An appropriately trained patient may continue the repeated drainage and scarification required by this method at home.[14]

Another technique is cyst aspiration with a large-bore needle, followed by instillation of corticosteroids (triamcinolone, hydrocortisone, betamethasone) with or without lidocaine. Some practitioners prefer to inject proteolytic agents, such as hyaluronidase, in lieu of steroids, but this may be potentially more risky given the communication of the cyst with the joint.[15]  Corticosteroids may be of benefit in the spectrum of ganglionlike cysts of the digits.[16]

Cryosurgery has been used to treat digital mucous cysts. Carbon dioxide snow, cryoprobes, and the intermittent spray technique have been used.[17]

Sclerotherapy was considered a quick and effective method of treatment.[18] Among the sclerosants infused were Morton fluid, iodine and carbolic acid, sodium morrhuate, ethanolamine, sodium tetradecyl, and polidocanol. Some consider sclerotherapy a dangerous approach because of the potential for extravasation of the chemical into the joint or tendon sheath. However, a 2008 study reported effective treatment of digital mucous cysts with percutaneous sclerotherapy using polidocanol.[19]

Curettage of the cyst may be attempted, and this may or may not be combined with electrodesiccation. Caution should be exercised to reduce the risk of scar.

High-intensity light sources recently have demonstrated at least short-term success in the management of digital mucous cysts. Cysts have been vaporized with the carbon dioxide laser and treated with infrared contact coagulation.[20, 21]

Dermatologic and plastic surgeons have practiced cold-steel surgical excision of digital mucous cysts for several decades. This procedure ranges from simple excision of the cyst to wide, radical excision with possible graft[22] or flap reconstruction. Flaps used for reconstruction have historically been rotation flaps,[23] but rhomboid flaps[24] as well as advancement flaps[25] have been used safely and reliably and may be easier to apply in selected situations.

Another approach is marsupialization, or excision of the whole proximal nail fold, with subsequent healing by secondary intention.

In recent years, excision and debridement of joint osteophytes has been recognized as a necessary adjunct to reduce the risk of recurrence. Some hand surgeons believe that excision and debridement of the marginal osteophyte without removal of the cyst itself may be the best intervention. This results in less postoperative impairment in joint motion and fewer nail deformities since cyst dissection around the germinal matrix potentially may injure the underlying matrix and cause scarring. In general, more aggressive dissection leads to fewer recurrences and more nail deformities.

More recently, nail surgeons have attempted to treat recurrent or refractory cysts by repairing the causative leak of joint fluid in such lesions.[26] Methylene blue dye is first injected into the distal interphalangeal (DIP) joint. Then, a skin flap is raised around the cyst to find the area of dye-filled communication between the joint space and the cyst. This communication is then sutured shut and the flap is dropped back into place without tissue resection.

Overall, significant disagreement exists in the literature regarding optimal treatment approaches.

Dermatologists tend to favor more conservative treatments such as multiple needling or aspiration followed by steroid injection; they have reported high success rates and relatively low risks of recurrence.

Hand surgeons have noted success and rare recurrence with osteophyte excision and debridement, but their patient population is comprised of those who fail other treatments. All of the literature is biased toward the minority of patients who seek medical care for their digital mucous cysts. Asymptomatic cysts and spontaneous regression appear to be common, with several series suggesting that the likelihood of the latter may approximate 50%.

Additionally, as the aggressiveness of interventions to treat digital mucous cysts increases, the associated costs also increase. Conservative treatments offer the prospect of low cost, low morbidity, and the elimination of disability and time loss related to recovery from surgery.

Consequently, a reasonable treatment plan for symptomatic digital mucous cysts may entail initial needling or aspiration and injection; if these modalities fail repeatedly, patients may be referred to a hand surgeon for more radical surgery but must be forewarned of the increased risk of complications and offered the option of simply deferring treatment for this essentially benign entity.

Consultation with a dermatologist, dermatologic surgeon, and/or hand surgeon may be warranted.

Digital mucous cysts (DMCs) have a high incidence of recurrence after treatment, typically occurring within 3 months of treatment. Sclerotherapy can result in extravasation of the sclerosant into the joint space. Short freeze-thaw cycles should predominate when cryotherapy is applied to avoid possible scarring of the nail matrix. Local depigmentation has been reported after steroid injection with triamcinolone.

Surgical interventions, while possibly slightly more effective in preventing recurrence, have many associated complications. Radial or ulnar deviation of the distal interphalangeal (DIP) joint with resulting impairment in joint motion can occur. While some nail deformities may be corrected by surgery, residual nail deformities may persist or be created de novo. Other complications include tendon injury, superficial infection, DIP septic arthritis, increased arthritic symptoms in the joint, and persistent swelling, pain, numbness, and stiffness.

Many medications have been used for the treatment of digital mucous cysts. At present, injectable corticosteroids commonly are used, and the most frequently administered agent is triamcinolone acetonide. If a ruptured or partially treated cyst becomes infected, antibiotic therapy with a penicillin or cephalosporin (eg, cephalexin) may be indicated. Silver nitrate and heparin cream also have been used. Currently, no standard doses exist for heparin or for silver nitrate.

Class Summary

Corticosteroid therapy may result in involution or shrinkage of the cyst. These agents have anti-inflammatory properties and cause profound and varied metabolic effects. In addition, these agents modify the body's immune response to diverse stimuli.

Triamcinolone (Aristocort)

Triamcinolone is used in dermatology for its anti-inflammatory and antipruritic properties. It decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing capillary permeability. Dilute triamcinolone with isotonic sodium chloride solution to a concentration of 2.5-5 mg/mL prior to injection. The total quantity injected may be 0.10 mL or less and a 30-gauge needle is used.

Class Summary

These agents treat skin and skin structure infections caused by susceptible organisms.

Cephalexin (Keflex, Biocef)

Cephalexin is a first-generation cephalosporin that arrests bacterial growth by inhibiting bacterial cell wall synthesis. Cephalexin has bactericidal activity against rapidly growing organisms. Its primary activity is against skin flora, and it is used for skin infections or prophylaxis in minor procedures.