Therapath Neuropathology

Neuropathic Pain

"Diagnosing small fiber neuropathy allows the physician to identify the cause of the pain and guide potential treatment..."

Small fiber neuropathy is a common cause of unexplained pain and can be associated with fibromyalgia and CRPS.1 The neuropathy is often distal, preferentially affecting the arms and legs, but can also be multifocal, or non-length dependent with pain on the torso or face. The pain can fluctuate, but is often more severe at night, and shows an inverse relationship with quality of sleep.2 EMG and nerve conduction studies are typically normal, as they assess the large, but not small nerve fibers.

Diagnosing small fiber neuropathy allows the physician to identify the cause of the pain and guide potential treatment options.3 When neuropathy is diagnosed, therapy can include treatment of the underlying cause, pharmacological intervention, and spinal or dorsal root ganglia neuromodulation.4,5 Pharmacological treatments include serotonin-noradrenaline reuptake inhibitors, anticonvulsants acting at calcium channels, topical lidocaine, and opioids.6

The diagnosis of small fiber neuropathy is most reliably made by punch skin biopsy with enumeration of the nerve fiber density at standard sites in the skin. Both the epidermal and sweat gland nerve fiber densities can be assessed for greater sensitivity.7

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References

1.
Oaklander A, Downs H, Herzog Z, Klein M. Small-fiber polyneuropathy (SFPN), a common underlying diagnosis in syndromes involving unexplained chronic pain and multi-system symptoms. Mol Pain. 2014;10(Suppl 1):O12. [PMC]
2.
Brouwer B, van K, Bouwhuis A, et al. The Pain Dynamics of Small Fiber Neuropathy. J Pain. 2019;20(6):655-663. [PubMed]
3.
Görlach J, Amsel D, Kölbel H, et al. Diagnostic utility of small fiber analysis in skin biopsies from children with chronic pain. Muscle Nerve. 2020;61(2):173-181. [PubMed]
4.
Falowski S, Pope J, Raza A. Early US Experience With Stimulation of the Dorsal Root Ganglia for the Treatment of Peripheral Neuropathy in the Lower Extremities: A Multicenter Retrospective Case Series. Neuromodulation. 2019;22(1):96-100. [PubMed]
5.
Simpson E, Duenas A, Holmes M, Papaioannou D, Chilcott J. Spinal cord stimulation for chronic pain of neuropathic or ischaemic origin: systematic review and economic evaluation. Health Technol Assess. 2009;13(17):iii, ix-x, 1-154. [PubMed]
6.
Fornasari D. Pharmacotherapy for Neuropathic Pain: A Review. Pain Ther. 2017;6(Suppl 1):25-33. [PubMed]
7.
Weaver J, Kim K, Carey B, Langsdorf J, Chin R. Gender Differences in Skin Biopsy Findings in Small Fiber Neuropathy: A Retrospective Chart Review. J Clin Neuromuscul Dis. 2018;20(2):69-75. [PubMed]