As fibromyalgia (FM) has gained wider acceptance and awareness in the medical community, this study inquired if any overdiagnosis of the disease occurred in a group of 321 women in a rheumatology clinic. Over a one-year period, 35 patients were diagnosed with FM.

An additional 11 women had received a presumed diagnosis of FM when in fact their condition was unrecognized spondyloarthropathy.

The authors hypothesize on the misdiagnosis. There is an evident overlap in symptoms between the two conditions. The authors compare the two:

"Both conditions frequently present with a long history of ongoing ill-defined pain, associated with sleep disturbance and prominent symptoms on awakening. However, the intensity and localization of spinal pain to fairly specific sites in the neck, midthoracic, anterior chest wall, or lumbar regions in the patients with spondyloarthropathy is somewhat different from the diffuse and ill-defined muscular pain of FM. Although both illnesses cause sleep disturbance, our patients reported prominent night spinal pain that awakened them from sleep, rather than a complaint of simply restless sleep. Nine of the 11 spondyloarthropathy patients had inflammatory type pain involving at least 2 of these sites."

The authors noted that spondyloarthritis has a prolonged course, evolving over 10 years. However, radiological changes of sacroilitis may not be apparent at onset or over time. Therefore, physicians can not be reliant on radiological sacroiliitis for diagnosis. The researchers report, "In a 10 year follow up study of 54 patients presenting with inflammatory type spinal pain, all of whom lacked radiological sacroiliitis at study entry, 32 were finally diagnosed with definite ankylosing spondylitis, and a further 10 with possible or undifferentiated sponyloarthropathy."
The authors stress that FM diagnosis does not exclude the possibility of other conditions causing the same symptoms. "Now that FM is an accepted diagnosis, it is possible that it may be used too freely in patients with ill-defined pain."

Fitzcharles MA, Esdaile JM. The overdiagnosis of fibromyalgia syndrome. American Journal of Medicine 1997;103:44-50.