I couldn't find much research
against it but I read a few accounts of people that smoked MJ to alleviate the painful symptoms of Polycystic Kidneys and were quite happy with their decision. That was just a quick google search, I couldn't say with 100% certainty what the true answer is but I also could not find any information about MJ's relation to the worsening of / development of the disease. Wait for some more experienced users to chime in; but I have a feeling you're in the clear
Also how are you feeling about the diagnosis? Stay strong, my friend. We are here for you.