Case definition of FM
In 1990, the American College of Rheumatology published the criteria for the classification of fibromyalgia (Wolfe et al., Arthritis Rheum, 33:160-72, 1990).
Firstly, the patients all have a history of widespread pain. Pain is considered widespread when all of the following are present: pain in the left side of the body, pain in the right side of the body, pain above the waist, and pain below the waist. In addition, axial skeletal pain (cervical spine or anterior chest or thoracic spine or low back) must be present.
Secondly, the patients must experience pain in 11 of 18 tender point sites on digital palpation. Digital palpation should be performed with an approximate force of 4 kg. For a tender point to be considered ‘positive’ the subject must state that the palpation was painful. ‘Tender’ is not to be considered ‘painful’. The tender point locations to be examined are illustrated in the figure below.
For classification purposes, patients will be said to have fibromyalgia if both criteria are satisfied. Widespread pain must have been present for at least three months. The presence of a second clinical disorder does not exclude the diagnosis of FM.