Characteristic electron microscopic findings in the skin of patients with fibromyalgia—preliminary study

This blinded study was done to determine if there are any abnormal electron microscopic (EM) findings in the skin of fibromyalgia syndrome (FMS) patients, which might contribute to or be due to the increased pain sensitivity seen in this condition. Skin biopsy samples were obtained from 13 FMS patients and 5 control subjects. All tissues were prepared for EM examination by immediate prefixation in 2.5% glutaraldehyde for 2 h and postfixation in 1% osmium acid for 24 h. Ultrathin sections on grids were stained by uranyl acetate and lead citrate. Biopsies were read by an individual without knowledge of participant status. Five skin biopsies from healthy controls showed relatively even distribution of variegated sized unmyelinated axons sheathed well by complicatedly folded Schwann cell membranes. In tissues from 9/13 FMS patients, unmyelinated Schwann cells were noted to be ballooned, whereas this finding was not noted in any controls (p = 0.029). Axons in most patients trended towards being localized in the periphery of the unmyelinated Schwann cell sheaths (p = 0.002). Particularly, peripheral localization of axon in the unmyelinated Schwann cell sheath had a strong relationship with ballooning of Schwann cell (p = 0.042), simplified folding of Schwann cell sheath (p = 0.039) and smaller axon (p = 0.034). Myelinated nerve fibers were unremarkable. The EM findings seen in the skin of FMS patients show unusual patterns of unmyelinated nerve fibers as well as associated Schwann cells. If these findings are replicated in a larger study, these abnormalities may contribute to, or be due to, the lower pain threshold seen in FMS patients.