Background and aims
Patients with fibromyalgia (PFM) present neurological symptoms such as paresthesia, muscle weakness and ataxia. We previously hypothesized that FM is caused by (moderately) increased hydrostatic pressure in the spinal canal, to cause widespread radicular pain. Because hydrostatic pressure is the highest in the lower nerves, we hypothesize that EMG abnormalities are more prevalent in lower sacral than in lumbar nerve roots.
Methods
Retrospectively review of 17  EMGs of PFM. 

Results
Neurogenic motor unit potentials were seen in 0% of L2 myotomes, 8% of L3, 29% of L4, 71% of L5, 47% of S1, 94% of S2, and 76% of S3,S4. S1 Hoffmann reflexes were delayed in 41% and 88% showed delayed S3S4-supplied anal reflexes.
Conclusions
EMG shows abnormalities in the legs, feet and anal sphincter. Nearly all PFM show abnormalities of the lowest sacral nerve roots (S2 and S3,S4). These findings may suggest that hydrostatic cerebrospinal pressure in the spinal canal plays a role in the pathophysiology of FM.

ELECTROMYOGRAPHIC ABNORMALITIES OF THE SACRAL NERVE ROOT MYOTOMES ARE HIGHLY PREVALENT IN FIBROMYALGIA