I have a bump under my thumbnail. no other fingernails are affected. i have hypothyroidism. what could be the cause?

Not sure but it: Could just be from a bruise. Take care!

Nail Bump: Likely a single bump on a nail is caused by trauma. Nail disorders associated with thyroid disease are usually on multiple if not all the nails.

If your thyroid: Level has been normalized by the proper amount of brand name T4 replacement, the bump is not due to your thyroid. There are many possible causes. Have your doctor take a look at it and help figure it out.