HI! I had to comment as I am 78 but very same symptoms. . I have had RA for almost 40 years which with steroid daily use can cause this muscle wasting over time, but even my new sensations and abilities were odd. My hemotologist suggested having a neuro muscular over view at UCONN and I did. then they suggested a DNA testing - and THAT is what I want you to bring up . AFTER a biopsy (in gut - and all 6 gluts are torn) it turned out I have ADULT ONSET MUSCULAR DYSTROPHY!!! masked byt the RA and steroid symptom ! at 78!!!!
now there is NOTHING more they can do for MD ` but good to understand new,, conditions. Good luck - hope it is NOT but few might consider it. yes it is genetic and NO ONE in my family has ever had it. I have ONE mutated gene - rae but it is enough....mosaic too. check it out! note - all my 3 grown kids have a 50% change of having this too, but until Medicare they will not check, and then my 8 grands could>?!