Blodwyn and Adcan, as GPs nor rheumies were able to diagnose my PMR it remained untreated for a year during which I spent several months unable to get out of bed apart from travelling to rheumy appointments by ambulance and wheelchair. It wasn't until additional symptoms of pain in my head and jaw together with nausea and sickness arrived at the end of that year that both GCA and PMR were finally diagnosed. Once on steroids, I decided that I would research anti-inflammatory foods as a way of at least trying to get back some sort of control over my life.
I added oily fish several times a week including sardines (with bones - good for our bones), mackerel, salmon and trout. I also included daily beetroot, avocado, garlic and turmeric - adding the powdered variety of the latter to all suitable meals such as rissotto, pasta and varieties of casserole. I added lots of known diuretic foods to try and offset the risk of steroid-induced fluid retention, such as asparagus, garlic, fennel and melon. I ate 'live' yoghurt daily with my muesli before taking the steroids to protect my stomach (I was unable to tolerate the usual stomach protectors prescribed alongside the steroids), and added Manuka honey which has a load of health benefits, including being beneficial to our immune systems which can take a battering from the steroids.
I reduced my intake of refined carbohydrates, including bread (can increase steroid-induced weight gain). I substituted most white potatoes for sweet potatoes, and avoided parsnips. These foods turn to sugar in our bodies and could add to the risk of steroid-induced diabetes. I also completely avoided processed meats, and as much sugar as possible. Coffee, alcohol and sugar can stress the adrenal glands which are already suppressed by the steroids.
I definitely found that if I veered off this diet for any length of time, I would become aware of worsening pain/stiffness, and when I returned to it, particularly it seemed the oily fish, I would notice a difference. I only gained a few pounds in weight and in spite of starting on very high dose steroids (40mgs due to GCA), my bone density didn't deteriorate.
If you haven't had a bone density scan (DEXA) then do request one at the start of steroids to get a baseline reading. Also, ask for a Vitamin D blood test as any deficiency can lead to pain similar to that of PMR. Such deficiency is easily corrected by a short course of high dose Vitamin D3.
I hope some or all of this helps, and good luck.