Lumpy just had huge infected feet from the Demodex and secondary staph infection. He has never had a problem with interdigital cysts...knock on wood...I hope I didn't just jinx myself!

Please let me know if any of these help. Here are a couple of sites that might be helpful:
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/70800.htmInterdigital Cysts
http://thebca.org/basiccare.htmlThis is another problem that no one seems to be sure what the cause is but you'll know one when you see an angry red swelling pop up between the dog's toes. First examine the paw carefully, especially the underside between the pads to be sure there is no foreign matter (a thorn or such). If there is, take it out. Clean the area. Remedies include: (I) Soaking the paw in warm water and Epsom Salts or Massengale Douche solution, dry and rub in Panalog. (2) Desenex foot powder. (3) ,Preparation H. (4) Division 5 Bulletin formula. Have your veterinarian make this up for you One part 60% DMSO, one part Gentavet solution 50 mg. per ml. Apply one drop per day; rub in with a Q Tip. Do NOT use more than one drop, do NOT apply more frequently than once a day. If you start application at the first sign, this solution will prevent the cyst from developing. With all these treatments, it's best to continue the treatment for two to three days after the cyst is gone.