What Are The Symptoms Of Amyotrophic Lateral Sclerosis?

My husband is 57 years old and in the past 6 mths has lost about 40 lbs He is hard to understand when he speaks, and when he swallows he aspirated liquid into his lungs. He has been to a neurologist and she has done testing on his nerves, and says he may have als.He has had an MRI that confirms there is no evidence Of ALS in their findings.All of my husbands blood work is normal,he has had chest X-rays, still nothing. My husband has been working for the last 25 years in a building that asbestos has been removed in 5 years ago, is it possible he may have been affected by the asbestos or is it more probable that he may have ALS? His large muscles are fine he is working and still living a normal life.