It it my understanding from talking to the same neurologist that ALS is a diagnosis of exclusion. When everything is ruled out the last diagnosis is ALS.
Is that because ALS is such an unwelcome diagnosis that all alternative diagnoses are explored first?
Or is there some other reason for testing theories in that order?
Generally the exclusion method is used because there is no conclusive direct test (or the test itself is damaging). Alzheimer's has no direct test either to my knowledge, though there is a lot of work going on.