This is just too weird.... I'm dealing with exactly that same problem with my right arm. I can't raise my arm straight in front of me. It's super painful right in the shoulder joint. Mostly in the front, like you mentioned.
I had it ultrasounded and xray'd. Came back with bicep tendonitis. So I"m doing physio to treat it. My issue is that it is caused by the massive camera I lug around for my work. It's the position I have my arm in for up to 12 hours every weekend shooting a wedding. That 90 degree angle I have my arm at is the most stessful position for the shoulder to be in.
So are you doing repetitive stuff with your arm that would contribute to the pain? The physio guy did say that lupus will cause early deterioration of tendons, muscles etc. That's why I went for nearly a decade with absolutely no pain, doing my photography, and now I'm getting it. It's progressive apparently.
think about what you do on a daily basis and see if there's a job or something that is putting your arm in that 90 degree angle for a long period of time. Even sitting at the computer with your arm up using the mouse, etc, can cause it.
I hope this helps. I know how painful it is. I feel like I'm losing the use of my right arm too.....
I can do anything through Jesus Christ who strengthens me. I have learned in whatever state I am in,to be content. Phillipians 4:11-13
33 years old. Diagnosed with lupus in 2000. Fibromyalgia, anti-phospholipid syndrome(APS)(stroke),Sjogren's, Raynaud's, seizure disorder-(miraclulously disappeared!), Libman Sach's Endocarditis, vasculitis, sacroiliitis, arthritis (neck) . Prednisone, Imuran, Coumadin, Clobazam, Amitriptyline, didrocal, monopril, calcium, Cykolokapron, multi-vitamin, vitamin D, Magnesium, vitamin B6, Acidophilus