Fibromyalgia: microbial bile acids associated with symptom severity?

Recognized by the World Health Organization, fibromyalgia is characterized by generalized chronic pain, fatigue and sleep disorders. This pathology, which mainly affects women, is often difficult to manage due to a lack of diagnosis or appropriate treatment. A recent cross-sectional study might nevertheless give some hope: it looked at the role of the gut microbiota of fibromyalgia patients, and more specifically at certain bacteria producing secondary bile acids (SBAs).

A dysbiotic gut microbiota

The researchers thus closely examined the gut microbiota (stool samples) and circulating SBAs (blood samples) of 42 Canadian women suffering from fibromyalgia and 42 controls. They observed alterations in the relative abundance of several bacterial species involved in SBA metabolism in these patients: reduced presence of Bacteroides uniformis and B. thetaiotaomicron, known to synthesize an SBA called α-muricholic acid; depletion also of Prevotella copri, a bacterium that affects SBA synthesis and the expression of FXR, a hepatic nociceptor; increased abundance of Escherichia bolteae and Clostridium scindens capable of affecting the metabolism of other SBAs.

SBA alterations

This gut dysbiosis was accompanied by significant alterations in the serum SBA concentration, in particular α-muricholic acid, with levels on average 5 times lower in fibromyalgia patients. Furthermore, this depletion was correlated with pain intensity and fatigue. Thus the decrease in serum SBA levels, and in particular that of α-muricholic acid, could disrupt the normal pain inhibition mechanisms. The authors suggest a mode of action: the decrease in circulating levels of α-muricholic acid (inhibitor of the FXR receptor) and the possible increase in excitatory SBAs could lead to the activation of the FXR receptor, leading to hypersensitivity to pain.

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An objectified diagnosis in the pipeline?

A direct consequence of these observations is the possibility of detecting people with fibromyalgia on the sole basis of the concentration of these serum SBAs. This is a major step forward since diagnosis is currently based solely on subjective measurements. The model developed by the authors shows an accuracy of 91.7%, with a specificity of 90.5% and a sensitivity of 92.9%. Enough to fuel the hope of a future diagnostic tool.