What Causes Unintentional Weight Loss While Having Spinal Stenosis?

My husband has been losing weight unintentionally for almost a year. He has spinal stenosis. He also has stomach issues. He had his galbladder out in Dec. 2016, Still having issues. Found out that his stomach isn t emptying correctly. He is now on meds to help that . This past month he has developed extreme weakness in his legs. He has no reflex reaction in either leg or foot. He had an MRI for the whole spine on Monday, plus bloodwork to check his B-12, etc. He is 57 years old and has trouble standing up, walking, and walking. His thighs are stiff and both hurt. My question is what are the possible conditions that he might have?