Fibromyalgia, a chronic pain disorder, is difficult to diagnose because it produces little physical evidence of a disease process. If a fibromyalgia patient is experiencing muscle or joint pain, an MRI on the affected area of the body will not show any damage to the joints or muscle tissue. If a fibromyalgia patient is experiencing headaches, the head MRI or CT scan will come back clean. So, an MRI scan is not useful for diagnosing fibromyalgia like it is for diagnosing other conditions that cause pain, like arthritis or a soft tissue injury.
However, there is one difference between sufferers of fibromyalgia and healthy individuals that shows up on an MRI. You just have to use a different kind of MRI scan, called an fMRI (functional MRI) or brain scan. An fMRI uses the same basic principle as an MRI scan, which is using magnetic resonance to create an image of the inside of the body. The fMRI can detect activity in certain parts of the brain; when there is increased blood flow and oxygenation to certain parts of the brain due to higher metabolic activity, the area of the brain will light up on the screen.
If you perform an fMRI on someone with fibromyalgia and a healthy person without fibromyalgia, you can notice a difference in intensity of the pain response of their brains. For example, if a person with fibromyalgia had their finger squeezed with a certain pressure, the pain centers of the brain lit up on the fMRI. When the person without fibromyalgia had their finger squeezed with the same intensity, the pain centers did not light up. It took a pressure twice as hard to get a pain response out of the healthy person than the person with fibromyalgia, and a different area of their brain actually lit up. Even before the painful stimulus, the finger squeeze, was administered, the fibromyalgia patients had some activity in the pain processing areas of the brain. This means that these areas were more active during baseline readings, so fibromyalgia patients may feel some level of pain without any external cause, in addition to being more sensitive to external pain.
This evidence supports the hypothesis that fibromyalgia pain is due to a lower pain threshold in fibromyalgia sufferers. If there is a lower tolerance for pain sensations in fibromyalgia patients, chronic pain may be experienced that would not even be noticed at all in healthy individuals. The fMRI study was performed in 2002 on 32 subjects: 16 with fibromyalgia, and 16 without fibromyalgia. The study builds a strong case that, while there is no physical deterioration of the body in fibromyalgia patients, the pain experienced by them is real, not imagined. Fibromyalgia pain is based within the brain, but it exists in an objective, observable sense. While fibromyalgia is not well understood, it is an organic disorder, not a psychosomatic one.