Sense of Smell in Individuals with Fibromyalgia: a Tractography Study

The etiopathogenesis of fibromyalgia (FM), which affects millions of people worldwide, is still debated. Recent research provides significant evidence that there are changes in the functions of the central and peripheral nervous systems and the sense of smell. This study analyzed the clinical assessment results of the sense of smell in individuals with FM and examined the olfactory-related structures in the nervous system.

Thirty patients with FM and 31 age- and sex-matched asymptomatic controls participated in this cross-sectional study. Participants' sense of smell was assessed with the Connecticut Chemosensory Clinical Research Center (CCCRC) including the Butanol threshold test (BET) and Smell Identification Tests. The total number of fibers, mean fiber length, the ratio of the number of fibers in this pathway to the number of fibers in the whole brain of the same individual, fractional anisotropy (FA), mean diffusion (MD), axial diffusion (AD) and radial diffusion (RD) values were calculated by tractography. Additionally, entorhinal cortex volume calculation was performed in MriStudio and MriCloud software using Diffusion tensor imaging (DTI) data in DICOM format.

The BET and CCCRC test scores were lower in the FM group (p < 0.05). Similarly, the mean FA values of the olfactory tract were lower on both the right and left sides in the FM group (p < 0.05). However, the entorhinal cortex volumes were similar, and there was no correlation between the right and left FA values of the olfactory tract and the BET scores or CCCRC scores in both groups (p > 0.05).

Our study, which included participants' self-assessments and data obtained from central nervous system (CNS) images, supports the idea that individuals with FM have a decreased olfactory function. Decreased FA values in individuals with FM may be an indicator of impaired myelin structure and axonal adaptation in individuals with FM.