Hello and thankyou for posting your query at DoctorSpring.com
I have gone through your question and understand your concern.
I will answer it in two parts.

Osteopenia is age associated problem aggravated by steroid intake. You should be on anti-osteoporotic medications like Alendronate/Risedronate/Ibandronate etc.

It is a known fact that a stable medicine in any form of Rheumatic disease once tapered allows relapse of disease. I would suggest you to take Imuran and take steroids too. You will be fine. Your doctor will be able to taper it as before.
Your fatigue will be over once you are on steroids. Your doses of steroid shall be 1 mg per kg and Imuran 2-3mg per kg of body weight. These doses are standard dose based on best clinical practice. The drugs are standard drugs for polymyositis.

Regards

Hello, thankyou for the question.
You had achieved remission with Imuran and were doing great. If we speak of remission we have to mean drug free remission which is a rarity. With drugs most of the patient are in remission whether they are on Azathioprine, MMF, Cyclophosphamide, even methotrexate and added steroid. You will be surprised to know that 'the drug of choice' does not exist as some patients do well with some medication while others do on some other medicine. So if you want to know what will work as the best medicine it is a matter of fact by only trial and error. In your case getting steroid back for some time will be the best policy. Sometimes we may resort to I.V Ig to induce remission and continue with Imuran. I also use Rituximab to induce and maintain remission. It has least side effects. The last two medicines are quite costly. Practice of medicine becomes complicated as we have to assess disease cost implication etc.

I would advise you to please continue Imuran and steroid . Induce remission with these drug and maintain it with Imuran and low dose of steroid.
You will be fine.
I hope this has helped.
Thankyou
Regards.