Comparing the ICD-11 chronic pain classification with ICD-10: how can the new coding system make chronic pain visible? A study in a tertiary care pain clinic setting.

Pain is a frequent reason for patients to ask for medical services. However, systematic information about the extent and impact of pain, especially in developing countries, has not been available up to now. We evaluated whether the 11th edition of the International Statistical Classification of Diseases and Related Health Problems (ICD) can fill this gap by coding all electronic out-patient medical records of the pain clinic at Siriraj Hospital in Thailand in 2019 (8714 visits), using the ICD-10 and ICD-11 browsers referenced on the WHO websites. The 3 most frequent pain-related codes in ICD-10 were R52.2 "other chronic pain" (29%), M54.5 "low back pain" (18%), and M79.6 "pain in limb" (13%). In ICD-11, the 3 most frequent codes were MG30.31 "chronic secondary musculoskeletal pain associated with structural changes" (28%), MG30.51 "chronic peripheral neuropathic pain" (26%), and MG30.10 "chronic cancer pain" (23%). Thus, using the currently valid ICD-10 system, roughly one-third of patient encounters were coded as "other chronic pain," and the next 2 were specifying the pain region rather than any underlying cause. By contrast, ICD-11 coding of the same patients identified underlying causes (bones and joints, somatosensory nervous system, cancer, or surgery), which provide guidance towards differential patient management. In our pain clinic, most patients suffered from chronic cancer pain, chronic neuropathic pain, and chronic secondary musculoskeletal pain, which were poorly defined or nonexistent in the current ICD-10 coding system. Compared with the ICD-10, the ICD-11 provides more detailed diagnostic categories and is more informative for clinical use, research, and resource allocation for pain-related conditions.