Tender points are areas that cause pain but do not display the typical signs of discomfort, such as heat, redness, or swelling.

The eighteen tender points consist of nine bilateral sites adding up to eighteen in total. The picture to your right shows the 18 tender point sites that have been identified by the American College of Rheumatology (ACR). According to the ACR criteria, FM is present when a patient suffers widespread pain for at least three months and feels pain in 11 or more of the 18 pressure point sites.

Doctors measure these tender points in one of two ways:

• by simply pressing the site with a finger or
• by using a slightly higher-tech method called dolorimetry.

In the dolorimetry method, the examiner presses a rubber endplate, attached to a spring-loaded force gauge, into the tender point site with increasing force. Patients are then asked to say when they stop feeling pressure and start feeling pain.

As you can see from the picture, each set of tender points are color coded. Each color identifies a tender point location.