Small fiber neuropathy and neurovascular disturbances in diabetes mellitus.

Functional and organic abnormalities in small unmyelinated C fibers are the hallmark of type 2 diabetes. These may be silent clinically or present with burning feet, neurovascular abnormalities, wherein warm, cold, and heat pain thresholds are disturbed in association with impairment in skin blood flow and loss of PGP 9.5 immunostaining nerves in the skin. There is a dysfunctional phase preceding organic structural damage to the neurovascular unit. It coexists with elements of the metabolic syndrome, particularly insulin resistance (IR), elevated systolic blood pressure, and diabetic dyslipidemia i.e. dysfunction of the neurovascular unit may contribute to IR due to compromised blood flow with decreased delivery of fuels to their target tissues. If this proves to be the case, it will become important to re-focus energies on the defective neuropeptidergic regulation of blood flow as an approach to ameliorating diabetes. Because there is a functional phase that precedes structural damage, reversibility of the defect is achievable.