Question: When a physician injects more than three muscles on each side of the upper back, can I use modifier 50 (Bilateral procedure) to report each side's trigger point injection (TPI)? Michigan Subscriber Answer: When the physician injects three or more muscles, you should report 20553 (Injection[s]; single or multiple trigger point[s], three or more muscle[s]) without units or modifiers, regardless of whether the muscles were on one or two sides. In 2004, the AMA revised trigger point injection codes 20550-20553 so that physicians would report either 20552 (... single or multiple trigger point[s], one or two muscle[s]) or 20553 once per session, regardless of the number of injections given. You should apply 20552 when the surgeon injects one or two muscles. Claim 20553, in contrast, when the surgeon injects "three or more muscles." Claims documentation should include the location of injections, number of injections and number of muscles.