Serum Serotonin levels are not low in Fibromyalgia; they are only low in FM subjects on antidepressants. This would explain why antidepressants do not have a major effect on FM.
Clin J Pain. 2011 Mar 16. [Epub ahead of print]
A Deficit in Peripheral Serotonin Levels in Major Depressive Disorder but not in Chronic Widespread Pain.
Paul-Savoie E, Potvin S, Daigle K, Normand E, Corbin JF, Gagnon R, Marchand S. abstract here
SERUM LEVEL in FM, treated and untreated versus Major Mood Disorder
It hence appears that reduced serotonin in periphery is an artifact created by antidepressant use. This lowered level did not translate into increased sensitivity versus other group. Don’t think we can use serotonin as a indication for FM though they did not do CSF/spinal fluid serotonin levels. A comparison with major mood disorder didn’t mean much because they would also be on antidepressants