Title:Role of Mechanoinsensitive Nociceptors in Painful Diabetic Peripheral
Neuropathy
Volume: 18
Issue: 5
Author(s): Mikhail I. Nemenov*, J. Robinson Singleton and Louis S. Premkumar*
Affiliation:
- Department of Anesthesia, Stanford University, Palo Alto, CA, USA
- Lasmed LLC, Mountain View, CA, USA
- Department of Pharmacology, SIU School of
Medicine, Springfield, Illinois, USA and Ion Channel Pharmacology LLC, Springfield, IL, USA
Keywords:
Diabetic peripheral neuropathy DPN, painful diabetic neuropathy PDPN, aδ-mechano heat sensitive AMH, Cmechano heat sensitive CMH, C-mechano insensitive CMi, transient receptor potential vanilloid 1 TRPV1.
Abstract: The cutaneous mechanisms that trigger spontaneous neuropathic pain in diabetic peripheral
neuropathy (PDPN) are far from clear. Two types of nociceptors are found within the epidermal
and dermal skin layers. Small-diameter lightly myelinated Aδ and unmyelinated C cutaneous
mechano and heat-sensitive (AMH and CMH) and C mechanoinsensitive (CMi) nociceptors
transmit pain from the periphery to central nervous system. AMH and CMH fibers are mainly located
in the epidermis, and CMi fibers are distributed in the dermis. In DPN, dying back intra-epidermal
AMH and CMH fibers leads to reduced pain sensitivity, and the patients exhibit significantly
increased pain thresholds to acute pain when tested using traditional methods. The role of CMi
fibers in painful neuropathies has not been fully explored. Microneurography has been the only
tool to access CMi fibers and differentiate AMH, CMH, and CMi fiber types. Due to the complexity,
its use is impractical in clinical settings. In contrast, a newly developed diode laser fiber selective
stimulation (DLss) technique allows to safely and selectively stimulate Aδ and C fibers in the
superficial and deep skin layers. DLss data demonstrate that patients with painful DPN have increased
Aδ fiber pain thresholds, while C-fiber thresholds are intact because, in these patients, CMi
fibers are abnormally spontaneously active. It is also possible to determine the involvement of CMi
fibers by measuring the area of DLss-induced neurogenic axon reflex flare. The differences in
AMH, CMH, and CMi fibers identify patients with painful and painless neuropathy. In this review,
we will discuss the role of CMi fibers in PDPN.