Revision of CFS Case Definition Underway
By Kim Kenney

A Case Definition Workshop convened by the Centers for Disease Control and Prevention (CDC) April 30-May 3 provided an exploration of the challenges of defining and studying CFS, as well as applying a definition for CFS in research, clinical and educational settings.

The participants represented multidisciplinary, multinational research efforts and the discussion was lively and occasionally intense. The serious, complex and “real” nature of CFS was not disputed once. As reported by CDC, the final outcome of the three-day workshop is a plan to “optimize” the case definition by 2002.

Consensus to cautiously approach revision of the case definition came early in the meeting. The implications for introducing a third CFS case definition are far-reaching. Of deep concern to many meeting participants was possibly jeopardizing the usefulness of research findings based on the 1988 and 1994 definitions by substantially re-defining the illness without scientific justification.

Since the existing knowledge about CFS rests on the selection of patients by applying prescribed symptom criteria, setting different criteria might describe a different patient population, and therefore yield different conclusions than the current literature documents. Imagine losing the knowledge of how many people have (conservatively defined) CFS, simply by changing what CFS means. Imagine making a diagnosis of CFS based on a test result that is positive for only a portion of what are now called CFS patients.

For example, if CFS “caseness” would depend on having both a positive upright table tilt test and a positive RNase L test, what label would be used for those patients who no longer meet the new CFS definition? And how would this change affect disability benefits and other medical-legal issues for patients who now carry a CFS diagnosis?

In fact, the issue of whether the definition of CFS should be broadened (say to include all persons with chronic unexplained illness)
or narrowed (to a large or small subset of those patients who meet the current case definition) was at the very heart of the discussion. The group recognized that additional data needs to be collected before making a final decision, and agreed to resolve those issues
to the best of their ability over the next two years so that the process can move forward.

Most researchers and clinicians find inadequacies in the 1994 definition. Symptom criteria lacks descriptors for severity, duration and frequency. Some lifelong exclusions (such as anorexia and melancholic depression) may result in under-reporting of CFS. Several
exclusions discount the possibility for CFS to co-exist with other common health conditions. Other criteria was based on little more than opinion (like the obesity cut-off set at a body mass index of 45), and no studies have been done to validate them.

There is much that can be done to improve the consistent application of the case definition by researchers and clinicians. In the meantime, researchers are urged to better describe their selection criteria for patients and controls so that study results can be more easily interpreted.

For instance, if an investigator insists that the onset of patients’ illness be documented as following a viral illness in order to be accepted into a study, this must be stated in the research report so that conclusions are not necessarily extended to patients with more gradual onset or patients with onset following environmental exposure or other events.

With progress being made by several research groups exploring biomarkers for CFIDS, a definition based on descriptive language for a collection of symptoms may be unnecessary by 2002. I for one certainly hope so.

Kim Kenney is President & CEO of The CFIDS Association of America and a participant in the CDC CFS Case Definition Workshop held in May 2000.