Yes. Some MD schools offer a Neuro Department letter. But you're at a DO school, so that's not an option. So you need at least 1 more letter, probably better to have 2.
You are very late with this. ERAS opens on 9/28. LOR processing tends to take 5+ days. You'll want to assign the letter to programs before ERAS opens (ideally). Realistically you need this letter written and submitted by the end of next week if you want it in your app for opening day. Monday is a holiday. Faculty are busy. Do not delay.