ALTHOUGH 'tender points' and 'trigger points' are often used interchangeably throughout fibromyalgia literature, fibromyalgia is diagnosed by fixed tender points, not trigger points. "A trigger point is a localized spot within a firm area of muscle that elicits a characteristic pattern of radiating pain, tingling, or numbness in response to sustained pressure" ¹. In contrast, tender points can occur in muscle, ligament, tendon, or periosteal tissue. Tender points elicit localized rather than radiating pain during sustained stimulation ².

There are no routine laboratory tests or x–rays that show abnormalities diagnostic of fibromyalgia. A physician's diagnosis of fibromyalgia is based on taking a careful history and finding at least 11 of the 18 characteristic tender points. Characteristic fibromyalgia tender points cluster in regions around the neck and shoulders, the upper chest wall, and the lower back. Because additional symptoms often occur simultaneously with fibromyalgia, further diagnostic studies may be needed to identify concomitant conditions ³. Frequently misdiagnosed, fibromyalgia is often confused with myofascial pain syndrome, hypothyroidism, rheumatoid arthritis, chronic fatigue syndrome, and systemic lupus erythematosus, any of which may occur concomitantly with fibromyalgia ⁴.

In conducting a fibromyalgia examination, tender points are "palpated bilaterally at each site using the thumb or first two fingers" applying steady, uniform pressure (4 kg) firmly enough to blanch the examiner's fingernail ⁵. The examiner palpates over the site gently and feels for spasms while examining the skin for redness and tenderness. Increasing pressure is applied until the patient grimaces, withdraws in pain, or tells the examiner to stop because of the pain ⁶. If a patient has typical fibromyalgia symptoms but does not meet the tender point criterion, the physician may diagnose the patient as having 'possible fibromyalgia' and assign trial therapeutic treatment ⁷. Tender points may be more evident on some days than others, calling for follow–up examinations.

Prior to 1990, diagnosis of fibromyalgia was based exclusively on subjective data. In 1990, the American College of Rheumatology (ACR) established criteria for diagnosing fibromyalgia. The criteria is as follows ⁸:

1. History of widespread pain which has been present for at least three months.

Definition:

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. In this definition, shoulder and buttock pain is considered as pain for each involved side. 'Low back' pain is considered lower segment pain.

2. Pain in 11 of 18 tender point sites on digital palpation.

Definition:

Pain, on digital palpation, must be present in at least 11 of the following 18 sites:

For a tender point to be considered 'positive' a person must state that the palpation was painful. 'Tender' is not to be considered 'painful.' Patients will be said to have fibromyalgia if both criteria are satisfied. Widespread pain must have been present for at least 3 months. The presence of a second clinical disorder does not exclude the diagnosis of fibromyalgia.

2. Krsnich–Shriwise, "Fibromyalgia Syndrome."

3. Krsnich–Shriwise, "Fibromyalgia Syndrome."

4. DL Goldenberg, "Controversies in Fibromyalgia and Myofascial Pain Syndrome," In Evaluation and Treatment of Chronic Pain, Edited by GM Arnoff, (Baltimore, Maryland: Williams & Wilkins, 1992).

5. Krsnich–Shriwise, "Fibromyalgia Syndrome," 69.

6. Krsnich–Shriwise, "Fibromyalgia Syndrome."

7. DA Nye, "Fibromyalgia: A Physician's Guide," 4 November 1998, <http://www.hsc.missouri.edu/~fibro/fm-md.html> (4 May 1999).

8. F Wolfe, HA Smythe, MB Yunus, RM Bennett, C Bombardier, DL Goldenberg, P Tugwell, SM Campbell, M Abeles, P Clark, et al., "The American College of Rheumatology 1990 Criteria for the Classification of Fibromyalgia: Report of the Multicenter Criteria Committee," Arthritis and Rheumatism 33, February (1990): 160-172.