Hi @ambershe, welcome to Mayo Clinic Connect. I also have polymyalgia rheumatica (PMR) but it is currently in remission. I've had two occurrences of it 6 years apart. The first time it lasted about 3 years, all of the while I was trying to taper off. My rheumatologist helped me with a tapering plan. I also learned that it's different for everyone but the key is slow and easy. Like other members have mentioned, I don't really think they know what causes it other than they think the bodies autoimmune system attacks connective tissues and they think it may involve genetics. My mother had rheumatoid arthritis so it made sense to me since my rheumatologist explained it in layman's terms to me as arthritis all over the body. Sometimes even 1/2 mg dosage changes up or down can make a difference when tapering. This last occurrence of PMR I had I did most of the tapering on a weekly basis and if the pain was too much at the next lower dosage I bumped it up half of the decrease that brought the pain for 3 days to see if the pain would go away or become more tolerable.

Here's some information that talks about white blood count and prednisone dosage.

Prednisone-induced leukocytosis. Influence of dosage, method and duration of administration on the degree of leukocytosis.
-- https://www.ncbi.nlm.nih.gov/pubmed/7304648

Did your doctor give you a tapering plan? I used a 2 week plan and sometimes went down to weekly or every three days when I felt really good. The key for me was working on healthy eating and some form of mild exercise without over doing it. Key word for me was "working" on it because it was hard for me to break some really bad snacking habits. Another tip someone passed on to me was eating foods that help fight inflammation -- https://www.health.harvard.edu/staying-healthy/foods-that-fight-inflammation