We dont know the cause - major bleed was ruled out as was a problem with bone marrow. This was back in September and after steroids, Azathioprine, we thought we were getting somewhere but he came off the Azathioprine and the platelet count went back down to the into the 40s. Started him on this again and although they platelet levels initially went up the red blood cells went down. Now although he is still on it the platelets are decreasing and now in the 50s. Vets dont seem too sure as to what is going on but considering when he went into the vets he had zero platelets I guess even 40-50 is good.