The effective treatment of pain and pain-related conditions rests upon the establishment of an appropriate diagnosis. Many types of pain, particularly musculoskeletal pain, are not attributable to a specific known pathology. The use of the International Classification of Diseases (ICD) as a standard system for diagnosis coding does not always allow clinicians to make a specific diagnosis that can utilize evidence-based medicine (EBM). EBM begins with the specific classification of a condition and leads to the use of current best practice in making decisions about patient care. EBM has limited applicability to those conditions that lack a specific classification. For those types of conditions, which include pain, the correlation between an ICD diagnosis and the type of treatment rendered is quite low. Unfortunately, on a population-level, an ICD code is often the only piece of information available that is related to diagnosis. Rather than discard this information because of its lack of specificity, an alternative method has been developed.

It is possible to group ICD codes into categories that can better guide a clinician's approach than an ICD diagnosis, particularly in the absence of conditions that are well-defined. Conditions can be classified as malignant or benign, well-defined (i.e., well-suited to EBM) or ill-defined, and acute, acute/chronic, or chronic. The combination of these three categories yields 12 subcategories that describe all patients. As disease classification becomes more specific resulting in the application of evidence-based medicine, this system allows for reclassification within the subcategories (e.g., from an ill-defined to a well-defined condition). This system is optimal for classifying a patient presenting with pain of unknown etiology, since it provides a framework in the absence of clearly defined guidelines. A working example of this classification system from a population of 50,000 pain patients will be presented.