It is commonly accepted that fibromyalgia can be difficult to diagnose. This is one of the reasons why it not known how many people are affected by the condition. The symptoms can vary and misdiagnosis is not uncommon as the symptoms can often present as they do in other conditions such hyperthyroidism (an underactive thyroid gland), chronic fatigue syndrome (myalgic encephalomyelitis or ME) and rheumatoid arthritis. It is thought that up to 5% of the population, i.e., 1 in 20 can be affected by the condition to varying degrees.
If someone is showing the signs of fibromyalgia then blood and urine samples are routinely taken and tested and these are the main diagnostic tests for these other conditions although, confusingly, it is not unknown for patents with such conditions to also have fibromyalgia at the same time.
According to the NHS, the most commonly used criteria for diagnosing fibromyalgia are:
- The presence of severe pain in 3 to 6 different areas or milder pain in 7 or more different areas
- Persistence of symptoms at a more or less constant and similar level for at least 3 months.
- No other explanation for the persistence of these symptoms has been identified.
For many years it was common to test 18 designated tender points around the body and a diagnosis would be given if at least 11 of the specified 18 pressure points must be painful when pressed. The 18 tender points are concentrated around the neck, chest, hips, knees and elbows and it is said that the pressure to be applied when testing should be just sufficient to cause the nail bed to whiten.
However, diagnosis of fibromyalgia is no longer based solely on the number of tender points as it once was. The American College of Rheumatology revised its criteria for diagnosing the condition in 2010 moving away from the reliance on testing tender points. That said, it is common medical practice for a GP, for example, to employ this test when suspecting that the patient may have the condition.