Thanks for writing in to Healthcare Magic!
Your problem started with the drumming, probably they are the sequelae of bad callosities only.
Some people have otherwise thick skin of the palms called familial hyperkeratoses and form very robust callosities.
When you quit the activity this will revert back toward baseline but some hardness will remain.
It is harmless and would be helpful if you want to resume druming.
If you just want them off your hands then use salicylic acid
and lactate based cream/patches like Corn
cap twice a day for a month.
If you have any further query please let me know I would try to answer it for you.
Wish you a great health!