  Fibromyalgia is a complicated and multifaceted disorder marked by widespread
chronic pain, fatigue, and muscle tenderness. Current explanations for the
pathophysiology of this condition include the Central Sensitization Theory,
Cytokine Inflammation Theory, Muscle Hypoxia, Muscle Tender Point Theory, and
Small Fiber Neuropathy Theory. The objective of this review article is to
examine and explain each of these current theories and to provide a background
on our current understanding of fibromyalgia. The medical literature on this
disorder, as well as on the roles of functional magnetic resonance imaging
(fMRI) and elastography as diagnostic tools, was reviewed from the 1970s to
early 2023, primarily using the PubMed database. Five prominent theories of
fibromyalgia etiology were examined: 1) Central Sensitization Theory; 2)
Cytokine Inflammation Theory; 3) Muscle Hypoxia; 4) Muscle Tender Point Theory;
and 5) Small Fiber Neuropathy Theory. Previous fMRI studies of FMS have
revealed two key findings. First, patients with FMS show altered activation
patterns in brain regions involved in pain processing. Second, the connectivity
between brain structures in individuals diagnosed with FMS and healthy controls
is different. Both of these findings will be expanded upon in this paper.
  The article also explores the potential for future research in fibromyalgia
due to the advancements in fMRI and elastography techniques, such as shear wave
ultrasound. Increased understanding of the underlying mechanisms contributing
to fibromyalgia symptoms is necessary for improved diagnosis and treatment, and
advanced imaging techniques can aid in this process.
