Dear friend,as you know H.S.Purpura is a immunological disorder.it will never be completely cured.as a side effect kidneys get affected by the deposition of immunological product.here what you are taking that is high dose of steroid ,is perfectly in sync with our standard treatment guideline.so you have to continue with this steroid even if your leg muscles get affected in steroid dependent myopathy.what you can do is a home or outfield regimen of physical exercise in the form of muscle stretching and muscle strengthening.it will help you a lot to overcome your muscle fatigue.than you.