I think positive EMGs are rare but when you have a positive EMG, there's no denying there is a nerve problem. The only question may be in interpretation of the exam.

My first EMG was positive showing a problem. By testing various nerves, they were able to pinpoint the problem to my brachial plexus rather than the neck, elbow or wrist. The doctor even spent extra time documenting the exam because it is rare to have a positive diagnosis for TOS using an EMG. Even though the exam upset the nerves, I was happy that someone finally believed me. The exams are worth the temporary discomfort.