I've not read about a toad's warts suddenly growing; but the leg swelling could be sign of an injury or bacterial issue. Both cases will probably require taking frog to a herp veterinary for x-rays or skin cultures.
Agree with Victor that the temperature sounds a bit low for a tropical species. Also, unless you test your water for the presence of chloramines and heavy metals, myself would recommend threat it with Seachem Prime. Good luck!