Hello, and welcome.
My problems came to light with muscle twitching, however, there are other problems that contain muscle twitching and atrophy. What exactly are you calling atrophy, have you lost weight, your arms shrunk or do you have "dents" in your muscles? Is there any weakness and / or cramping?
Can you give some information, like your age, what your neuro said in his report / testing.
Have you had an MRI of the brain?
More than likely, its something other than ALS, esp. with a clean EMG, however, if your still worried, you should seek out an ALS Clinic / MDA Clinic, as they are the experts and will be able to diag. your problem better than local neuros.
Please ask any questions you need.
Rgds,
Jamie