Question is how much pain is worth tolerating to keep reducing prednisone?
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I don't think you should keep reducing with increasing pain. Similarly, "tolerable pain" isn't a good reason to increase your dose. There isn't a correct way to taper prednisone. except to taper slowly as pain levels and side effects allow --- faster tapers for some ... slower tapers for others. Only you can decide how much pain is tolerable. Depending on the person, the side effects of Prednisone are also tolerable or intolerable.

Staying on the same dose is an option. You don't have to increase or decrease your dose. My rheumatologist told me a "stable dose" is also important
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CIMZIA is a prescription medicine called a Tumor Necrosis Factor (TNF) blocker. I don't want to second guess your doctor but TNF blockers aren't recommended for PMR.

EULAR/ACR guidelines for PMR say the following:

"The panel strongly recommends against the use of TNFα blocking agents for treatment of PMR."
https://ard.bmj.com/content/74/10/1799.full
These are only recommendations so there isn't any rule that says your doctor can't try Cimzia.
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Cimzia is a treatment for various types of inflammatory arthritis which have symptoms very similar to PMR. Maybe your doctor is leaning toward a diagnosis of inflammatory arthritis instead of PMR.