Question: A payer has denied our claim for a pain management office visit with the reason “Missing/Incomplete/Invalid principal diagnosis.” One of the billers is telling me that M51.16 and M51.26 cannot be billed together, but I’ve never seen anything stating this. There is an Excludes 1 for M51.1x, but I don’t see anything for M51.2x. Who is right? Louisiana Subscriber Answer: Your billing staff person is correct. When a patient has a herniated/displaced disc treated with radiculopathy, the correct ICD-10 diagnosis code is M51.16 (Intervertebral disc disorders with radiculopathy, lumbar region). This is a combination diagnosis code and includes the diagnosis associated with M51.26 (Other intervertebral disc displacement, lumbar region). You should only report M51.16 on the claim.