What laboratory investigations are useful in fibromyalgia?
All laboratory values in fibromyalgia are used for exclusionary purposes. There are no characteristic chemical, electrical, or radiographic laboratory abnormalities. However, several consistent investigational serum markers of the disease have been reported in the literature. An increase in cytokines, with a direct relationship between pain intensity and interleukin-8, has been reported. Other investigational findings include a decrease in circulating cortisol (this may play a role in decreased exercise tolerance), a decrease in branched-chain amino acids (perhaps correlating with muscle fatigue), and decreased lymphocyte G protein and Cyclic adenosine monophosphate (cAMP) concentrations. Four studies have shown an increase in Substance P in the cerebrospinal fluid in fibromyalgia. At present, these findings are not clinically useful for the diagnosis, prognosis, or monitoring of the treatment response of fibromyalgia patients. Sleep studies are often abnormal (“alpha-delta,” nonrestorative sleep), but the abnormalities are also seen in other chronic painful conditions. Functional magnetic resonance imaging (MRI) studies have shown augmented responses in the insula and anterior lingual gyrus to nonpainful sensory stimuli in fibromyalgia patients, but not in controls.