Question: I am on weekly Cytoxan therapy for SLE. I have developed severe joint pain, and also significant muscle pain in my upper extremities. Yes, I have obviously experienced joint pain during exacerbations, historically. This is markedly different. I am also attempting to taper down on Solu Medrol, while on Cytoxan. The goal is to get down to the lowest possible dose, for obvious reasons. Thus, I am concerned that this unprecedented pain may be a side effect. Thank you, in advance.

Good afternoon sir. The Cytoxan is 500mg IV weekly. I have tapered down from 12mg to 4mg of Solu Medrol daily, in recent months. Historically, I had a severe nephritis in 2007-8. This flare, we know based on clinical symptoms and the MRI, I have some new lesions in the peri ventricular white matter, and a vasculitis. "Cerebral vessels have a beaded appearance." I had HTN, and profound fatigue with weakness. I had been working 50+ hours/week happily until then. I did have an ACTH Stim test, and my cortisol was slow to recover, but did recover. CRP, Sed Rate are elevated.
The joint/bone pain FEELS as though the very marrow is ablaze, although I know logically that the cavity doesn't have pain receptors. The muscle pain is oddly primarily in my bilateral upper extremeties, largely above the elbows. It's unlike any muscle pain i have ever experienced in over 20 years with SLE. When weight bearing, then leg pain grows diffusely across my pelvis. Yes, I do realize that I may be deconditioned from less activity since beginning the Cytoxan. However the muscle pain in my upper arms is unrelenting, and they have grown so weak. I know pain and weakness are vague symptoms. I'm sorry about that. I just know it's different than ever before. The Cytoxan seemed the logical culprit. But the drug literature does not really refer to it heavily. Please help, sir. Thank you now, and for your work in Rheumatology.