This was the initial CPT Assistant that describes the use of 64640 for the lateral branches of S1-S4 contributing innervation to the sacroilliac joint. I think Michele provided you some great information but thought I would copy and paste this one in the situation you hadn't seen it before.
December 2009 page 11
Bonus Feature:Surgery: Nervous System
Question: Should code 64640 x 4 be reported per lesion because it is a single percutaneous entry point or should the unlisted code 64999 be reported? What is the appropriate code to use for radiofrequency (eg, Simplicity III™ Radiofrequency Probe) for sacroiliac (SI) joint nerve destruction from a single percutaneous entry site in the following procedure?
The Simplicity III electrode was then advanced, maintaining continuous contact with the sacrum, on a cephalad and slightly lateral line, staying lateral to the sacral foramen, medial to the sacroiliac joint, and ventral to the ilium, until contact with the sacral ala prevented further advancement. Appropriate positioning was confirmed by changing the caudal/cephalad tilt of the C-arm to parallel the superior endplate of S1; and verifying once again that the entire length of the Simplicity III electrode was advanced to the ipsilateral sacral ala and the three independent, active contacts were positioned adjacent to the S1, S2, S3, and S4 lateral branch innervation pathways.... "Lesioning" was then carried out using the Simplicity III preprogrammed protocol at 85 degrees centigrade for five minutes. Karen Glancy, CCS-P
Answer: Since the documentation indicates insertion of a single electrode (having three contacts) at the sacroiliac (SI) joint "to lesion the lateral branches of S1, S2, S3, and S4," code 64999, Unlisted procedure, nervous system, is reported once. This "SI joint rhizotomy" would be reported once using the unlisted nervous system code 64999. The sacroiliac (SI) joint and sacral anatomy differs in that it is comprised of spine bone and pelvic bone wherein the exact innervation of the SI joint occurring more from contributing branches at adjoining nerve levels. Procedurally, the work of the described SI joint destruction differs from that described by code 64622, Destruction by neurolytic agent, paravertebral facet joint nerve; lumbar or sacral, single level. Code 64622 may be reported for L5-S1 rhizotomy (nerve destruction since this joint lies between two spinal segments for which the anatomy and procedural work at L5-S1 is similar to that at other spinal segments (eg, L4-5). Therefore, the unlisted nervous system code 64999 would be reported once for SI joint or sacral rhizotomy (nerve destruction).
To differentiate between the work when performing sacral nerve destruction of S1, S2, S3, and S4, each individually separate peripheral nerve root neurolytic block is reported as destruction of a peripheral nerve, using code 64640, Destruction by by neurolytic agent; other peripheral nerve or branch. In this instance, code 64640 is reported four times. It is suggested that Modifier 59, Distinct Procedural Service, be appended as well.
It is very important that the service performed matches accurately with the descripton in the CPT code. Therefore, for this very reason, it is important to remember that a code that is "close" to the procedure performed is not selected in lieu of an unlisted code. There are some who maintain that they are not allowed to use unlisted codes or that the use of the unlisted codes is undesirable. While the use of an unlisted procedure code does require a special report or documentation to describe the service, correct coding demands that you use a code that is appropriate for the service being provided (ie, a code that most accurately represents the services rendered and performed).