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Condition

Mucous Cyst

A small fluid-filled bump that forms near the fingernail, almost always caused by arthritis in the joint just underneath.

What is a mucous cyst?

A mucous cyst is a small, firm, clear-to-white bump that appears on the back of the finger between the fingernail and the last joint. It is essentially a ganglion cyst that comes from the DIP joint (the joint closest to the nail), and it develops because of osteoarthritis in that joint. A small bony spur (an osteophyte) inside the arthritic joint pokes at the joint capsule, and the capsule leaks a small amount of joint fluid into the soft tissue under the skin. That fluid forms the cyst.

Because the underlying cause is arthritis, a mucous cyst often comes with the other features of finger arthritis — a bony bump on the side of the joint (a Heberden node), stiffness, and aching.

Common symptoms

  • A small, firm bump on the back of the finger just before the nail
  • A groove or ridge in the fingernail growing out from the cyst, because the cyst presses on the nail-forming tissue
  • Skin over the cyst that is thin, shiny, or occasionally breaks and drains clear, jelly-like fluid
  • Mild aching in the joint underneath

Why it matters — the infection risk

Most mucous cysts are bothersome but not dangerous. The concern comes when the overlying skin becomes very thin and the cyst ruptures. Because the cyst is connected to the joint, a rupture creates a direct pathway from the outside world to the joint. An infection that travels along that path causes a septic joint, which is a surgical emergency. A mucous cyst with skin that is breaking down, weeping fluid, or already draining should be seen promptly.

How it is diagnosed

The diagnosis is usually obvious from the exam. X-rays of the finger are helpful because they confirm the arthritis in the joint and show the bony spur that is causing the cyst — which matters for surgical planning.

Treatment options

Non-surgical treatment

  • Observation. A cyst that is small, not painful, and not threatening the skin can be left alone.
  • Aspiration. A small needle can be used to drain the cyst in the office. The cyst usually refills because the underlying joint is still producing fluid, but aspiration can be helpful as a short-term measure.
  • Do not pop. Squeezing or puncturing a mucous cyst at home is not recommended because of the infection risk mentioned above.

Surgical treatment

  • Cyst excision with osteophyte debridement. The definitive treatment. The cyst is removed along with the bony spur in the joint that is producing it. Removing the spur is the key step — if only the skin bump is taken off and the underlying cause is left behind, the cyst is very likely to come back.
  • Skin grafting or local flap. Occasionally needed if the skin over the cyst is very thin and a clean closure is not possible after removing the cyst.
  • DIP fusion. Considered when the underlying arthritis itself is painful and limiting, rather than just the cyst. Fusion removes the painful joint and eliminates any future cyst formation.

What to expect at your visit

Dr. Barrera will examine the finger and check x-rays. Most patients do not need surgery — a small, quiet cyst on a finger that is otherwise working well can be watched. When surgery is the right choice (painful cyst, bothersome nail deformity, or thinning skin at risk of rupture), it is a short outpatient procedure performed with local anesthesia. A splint is worn for about a week, then motion is resumed.

Dr. Barrera's approach

The key to a durable result is treating the joint, not just the skin bump. Removing the bony spur at the time of cyst excision dramatically reduces recurrence. When the underlying DIP joint is end-stage arthritic and painful, fusion addresses both problems in one operation.

When to call the office sooner

Call us if the skin over the cyst breaks open, if the cyst starts draining, if the finger becomes red, hot, and swollen, or if you have a fever. These can be early signs of a joint infection and need to be evaluated promptly.

Related

Hand osteoarthritis · Ganglion cyst

Questions?

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