Question: The neurologist treated a patient with “ALS.” What diagnosis code should I report for this encounter, and what is ALS — beyond the fact that it used to be called “Lou Gehrig’s disease”? AAPC Forum Subscriber Answer: You should represent a diagnosis of ALS, or amyotrophic lateral sclerosis, with G12.21 (Amyotrophic lateral sclerosis). Condition rundown: ALS is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord, mainly affecting motor neurons responsible for controlling voluntary muscle movement. As ALS worsens, afflicted individuals may experience muscle weakness, difficulty speaking, swallowing, and breathing.