What is a digital mucous cyst?
The digital mucous cyst is a ganglion cyst that arises from the end finger knuckle (the distal interphalangeal joint) or nail matrix and appears on the back of the fingertip 1.
The origin of the term digital mucous cyst: from Greek digitus = finger; mucous refers to a thick substance in the cyst; cyst = enclosed pouch.
- Mucinous cyst
- Digital mucoid cyst
- Periarticular fibroma
- Periungual ganglion
- Myxoid cyst
- Nail cyst
- Cystic nodule
- Reference: 1
Causes and Pathology
Mucous cysts most commonly occur in 40-70 years old individuals with osteoarthritis, more frequently in women 1. They can appear at any age but are rare in children 1.
Trauma may be a cause in some cases 2.
Digital mucous cysts are not hereditary; they are not caused by infection, do not spread, they are benign (they do not invade nearby tissues) and do not develop into skin cancer 6.
Some cysts arise from the distal finger knuckle due to degeneration of the tissues in the joint, but others seem not to be related with the joint and develop due to abnormal growth of the connective tissue cells (fibroblasts) under the skin 5.
Cysts are filled with a clear, thick jelly-like substance 6.
Symptoms and Signs
- A small, 1-10 mm or, rarely, bigger, firm, rubbery papule or lump on the upper (dorsal) side of the fingertip on any finger, mostly index or middle finger of the predominant hand or, rarely, on any toe may appear suddenly or over several months. A cyst can be partially translucent or bluish. Some cysts look like warts.
- One or more cysts on one fingertip or more fingertips can be present.
- The overlying skin can be thinned and partly translucent, or moderately thick and flesh-colored or rough as a wart.
- A cyst may appear under the nail, which can be depressed or have longitudinal grooves and red or blue lunula (a thin, normally pale, proximal part of the nail). Nail grooves may precede the cyst for as much as six months.
- A cyst can be tender to touch.
- Usually, only larger cysts are painful.
- Decreased range of motion in the last finger joint
- A cyst can spontaneously burst or disappear.
- References: 1,2,5
Picture 1. A wart-like mucous cyst on the middle finger
Picture 2. A mucous cyst on the finger. The skin over the cyst is thinned.
Picture 3. A mucous cyst on the thumb. The skin over the cyst looks thinned.
Picture 4. Mucous cysts on both thumbs
Picture 5: A mucous cyst behind the nail, which is deformed.
- A doctor can usually make a diagnosis from observation and palpation of the cyst.
- Transillumination reveals a translucent cyst.
- An X-ray may show bone spurs (osteophytes) in the distal interphalangeal joint, which are usually associated with osteoarthritis.
- Ultrasound, CT and MRI can all clearly show the cyst.
- Injection of methylene blue dye into the cyst 12 hours prior the surgery can reveal the extent and origin of the cyst during the surgery.
- References: 1,2,3
Picture 6. Transillumination of a mucous cyst.
A cyst is translucent, so light shines through it.
Note a longitudinal groove in the nail.
The digital mucous cyst may look like:
- Xanthomas – yellowish bumps in individuals with increased triglyceride levels.
- Bone spurs
- Herpetic whitlow
- Molluscum contagiosum
- References: 1,8
- Heat: soaking in warm water or applying warm compresses
- Ointments: corticosteroids, such as triamcinolone acetonide (complication: skin thinning or local depigmentation), heparin cream, silver nitrate
- Massage or compression with fingers
- Repeated puncture with a needle and draining may be effective in 70% cases (Video 2) 5
- Aspiration with a large-bore needle followed by an injection of steroids is not very effective (high rate of recurrence) 5
- Cryosurgery with carbon dioxide snow or cryoprobes (freeze-thaw-freeze method, ~30 seconds) is effective (up to 15% recurrence) 5.
- Sclerotherapy with an injection of polidocanol or Sodium tetradecyl sulfate 10 (complication: a sclerosant can leak into the joint). The treatment has a low recurrence rate 10.
- Chemical cauterization with phenol
- Curettage with or without electrodesiccation
- Carbon dioxide laser vaporization 7
- Infrared contact coagulation
- Cold-steel surgical excision with possible graft reconstruction has a high rate of recurrence 5.
- Surgical removal of a bone spur (osteophyte) with or without cyst removal. Possible complications include fingertip deviation, persistent swelling, stiffness, pain, numbness, impaired mobility, nail deformities, tendon damage, skin or joint infection. Some doctors believe wearing a finger splint for 2-10 days after the procedure can reduce discomfort 5.
- References: 4,5
NOTE: Striking a mucous cyst with a book is not recommended because of the possibility of a finger injury.
Video 2. Digital cyst drainage
- Stiffness or limited motion in the distal interphalangeal joint 9
- Treatment of a cyst under the nail can result in a permanent nail deformity 9.
Recurrence of a mucous cyst is common and typically occurs within 3 months of treatment 1. Surgical removal of the cyst and bone spurs has the lowest recurrence rate 4,5.
- Emedicine (Digital mucous cysts)
- Emedicine (Symptoms and signs)
- Emedicine (Diagnosis)
- Emedicine (Treatment)
- Aafp.org (Office management)
- The Australian College of Dermatologists (Digital mucous cyst)
- PubMed (Carbon dioxide laser vaporization)
- PMC (Case: 88-year old man with a mucous cyst)
- PMC (Treatment options)
- Pubmed (Sclerotherapy)