ALS is different in each person in how it starts, how it progresses, how quickly it progresses, etc.
My mother was just diagnosed with a type of ALS called Bulbar Onset ALS, which I believe is one that starts and progresses differently than people with "typical" ALS. Her symptoms do not affect her arms and legs at all. It started with slurred speech about 18 months ago, and we initially thought she had a mini-stroke or something. About 6 months ago, her slurred speech drastically worsened, her saliva production increased A LOT, and she started having trouble swallowing food. She had to have several tests done...MRI, EMG, blood tests, and a few others to rule out other possibilities, as there is not a specific test that can diagnose ALS yet...it is a process of elimination.
Not sure if you will get this response or not....I do not have ALS but my dad was diagnosed with it in 2005. He began noticing a nonstop muscle twitching in his left hand - and over about a month or two he also noticed the movement was slowed a bit, and seemed a bit weaker. MDs were a bit confused at first, and after a series of normal tests, he was led to a muscle biopsy in his thigh, which confirmed the ALS. But constant muscle twitching to one area along with progressive weakening seemed to be his symptoms.