What could be the cause of a hard bump on my left thumb joint?

Doctor's Answers 2

Photo of Dr Aaron Gan
Dr Aaron Gan

Hand Surgeon

This swelling over the dorsum of the interphalangeal joint (IPJ) of the thumb appears to be a mucous cyst. A mucous cyst is a fluid-filled balloon arising from the IPJ of the thumb. It is commonly associated with wear-and-tear, or osteoarthritis, of the IPJ of the thumb. Overuse and increased motion in the IPJ may cause more joint fluid to fill this cyst, which in turn causes an increase in:

  • pain,
  • redness and
  • swelling at this site.

Unfortunately, the only effective treatment for a mucous cyst is surgery. My preferred approach to treat a mucous cyst is decompression of the mucous cyst via a midlateral incision (not directly cutting into the cyst itself) and removing the osteophytes (bone protrusions as a result of the worn-out joint) which can cause irritation of the joint and recurrence of the mucous cyst.

This procedure avoids the complication of a skin defect resulting from directly excising the mucous cyst requiring a local flap procedure with additional scarring. A midlateral incision leaves a fine linear scar instead, and the skin overlying the mucous cyst remains intact and in original condition.

One may consider seeking treatment from a hand & wrist specialist to perform this delicate operative procedure.

Thank you for the email. From the picture, this does look like a digital myxoid cyst. This usually occurs over the distal finger joints and may be associated with underlying osteoarthritis. The cyst may have a connection with the underlying joint.

Some simple treatments includes rubbing and pressure over the area and freezing it with liquid nitrogen treatment, but the recurrent rates are high. Definitive treatment is through surgical excision of the lump.

There are other conditions that can mimick this such as epidermoid cyst or giant cell tumour of the tendon sheath, so if doubt, do visit your doctor to get the diagnosis confirmed.

Similar Questions

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Thanks for the question. I do think that you should see your dermatologist or gp early to get the cyst examined. That is is becoming red and painful is an indication that it may be becoming infected or inflamed. Your doctor will assess to see if antibiotics are required or if drainage or excision of the cyst is necessary.

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How is arthritis diagnosed in a young female with aching finger joints?

The aches and pain in your hand may not be entirely due to just "overuse". Arthritis means inflammation in the joints, typically we classified into 4 categories: 1. "Normal" wear and tear/ Aging (For e. g Osteoarthritis, Spondylosis) - these happens in every person, when you age, there will be more wear and tear, althought not everyone will have pain. It is very similar to a car, when the mileage hits a certain number, there is bound to be some wear and tear in the tyres. 2.

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