Case Definition

Overview

Defining what one means is crucial to conducting surveillance and other public health research.  For these purposes, CDC, the National Arthritis Data Workgroup, and others have methodically developed case definitions that include most of what might be considered to be arthritis or a related rheumatologic condition (e.g., fibromyalgia).  As such, the public health definitions are generally broader than that used by clinicians, but this has the advantage of incorporating related conditions that would otherwise be orphaned in comparisons of the burden and impact major medical conditions.  These definitions also make an effort to exclude musculoskeletal conditions that are major public health problems in their own right (e.g., osteoporosis, chronic back conditions) but are unlikely to include a high proportion of what one would consider to be arthritis. 

Because arthritis in children is generally different from that in adults, there are separate definitions for these age groups.  In addition, there are two definitions for adults that accommodate the general information that people are able to report themselves (“doctor-diagnosed arthritis”) and the more specific information available from medical encounters (the ICD-based “arthritis and other rheumatic conditions” or AORC).     

Finally, the media often shorten the more precise labels used for these definitions and instead use the term “arthritis.” This makes results more accessible to the public, but at the cost of a more precise understanding.  Sticking to the precise labels in scientific discussions and especially in publications will help advance the field.