What Causes Swelling In Hands?

hi, my mother has swelling in her hands every so often( mybe like once every 3 or 4 months). she has been to the doctor many times and has many test done but all they have to say is that she has low Vitamin D. she says that it starts off itching first and then it starts swelling. Her hands get so big she cant even close her hands or drive. do you have any idea what might be wrong with her hands?