While diagnosing MS has come a long way in recent years, it is not an exact science. That's because there is no definitive test to determine if someone has MS. A diagnosis is based on a number of factors, including patient history, a neurological exam, and the results of diagnostic tests such as magnetic resonance imaging (MRI). If you arrive at your primary care doctor's office with certain neurological symptoms in tow — say, fatigue as well as numbness in your left hand — you may be referred to a neurologist, a doctor who diagnoses and treats neurological disorders.