Cause of triceps and buttock fat loss.

Hello Doctor, I have notice issue on my triceps muscle, buttocks muscle tone reducing which causing tailbone pressure more qnd getting pain , as well calf muscle or under ties muscle tone reduced, I consult rheumatologist qnd did some test ANA , HLAB27 AND CPK ETC ALL NEGATIVE , as per blood qnd urine test taken recently normal not much issue , so is there any issue causing this muscle peotine loss , my weight reduction stopped now 64.8 maintaining before it was 68 an year back qnd reduced now to 64.8 , only suspect thyroid T4 in boarder range so what could be the reason this muscle weekness. Attached report, abdomen scan is normal except grade 1 fatty liver , and small Ambrical hernia with omental fat as content mean what , my concern is metion area fat loss happend mainly on buttock and triceps, calf .