Small fiber neuropathy or small fiber pathology?

Non-length-dependent small fiber neuropathy: Not a matter of stockings and gloves

The clinical spectrum of small fiber neuropathy (SFN) encompasses manifestations related to the involvement of thinly myelinated A-delta and unmyelinated C fibers, including not only the classical distal phenotype, but also a non-length-dependent (NLD) presentation that can be patchy, asymmetrical, upper limb-predominant, or diffuse. This narrative review is focused on NLD-SFN. The diagnosis of NLD-SFN can be problematic, due to its varied and often atypical presentation, and diagnostic criteria developed for distal SFN are not suitable for NLD-SFN. The topographic pattern of NLD-SFN is likely related to ganglionopathy restricted to the small neurons of dorsal root ganglia. It is often associated with systemic diseases, but about half the time is idiopathic. In comparison with distal SFN, immune-mediated diseases are more common than dysmetabolic conditions. Treatment is usually based on the management of neuropathic pain. Disease-modifying therapy, including immunotherapy, may be effective in patients with identified causes. Future research on NLD-SFN is expected to further clarify the interconnected aspects of phenotypic characterization, diagnostic criteria, and pathophysiology.

Small fiber neuropathy in Sjögren syndrome: Comparison with other small fiber neuropathies

INTRODUCTION

We compared histological and clinical profiles of primary Sjögren syndrome (pSS) small fiber neuropathy (SFN; pSS-SFN) with idiopathic SFN (i-SFN) and hereditary transthyretin amyloidosis SFN (hATTR-SFN) and described the evolution of pSS-SFN.

METHODS

All patients with pSS-SFN, i-SFN, and hATTR-SFN confirmed by reduced intraepidermal nerve fiber density on skin biopsy were retrospectively included, and their characteristics were compared. To analyze prognosis of pSS-SFN, patients prospectively underwent a second evaluation.

RESULTS

Fifteen pSS-SFN, 17 hATTR-SFN, and 11 i-SFN were included. Time to diagnosis SFN was longer in pSS-SFN and i-SFN than in hATTR-SFN. Painful and non-length-dependent patterns were more frequent in pSS-SFN than in hATTR-SFN. Twelve (80%) patients with pSS-SFN had a non-length-dependent pattern. Ten patients with pSS were reassessed after 3.1 years (1.7-4.7); none developed large fiber neuropathy linked to pSS.

DISCUSSION

Primary Sjögren syndrome SFN is characterized by a more frequent non-length-dependent pattern compared with i-SFN and hATTR-SFN. Primary Sjögren syndrome SFN did not evolve through large fiber neuropathy.

Small fiber neuropathy in unexpected clinical settings: a review

Small fiber neuropathy (SFN) is being recognized with increasing frequency in neuromuscular practice due to improved diagnostic techniques. Although there are some common etiologies, up to one-third of cases are considered idiopathic. In recent years, several disorders have unexpectedly been reported in association with SFN, on clinical grounds and complementary investigations, including quantitative sensory testing, intraepidermal nerve fiber density and confocal corneal microscopy. Knowledge of these disorders is important in clinical practice as increased awareness enables prompt diagnosis of SFN in these settings and early optimal therapeutic management of affected patients. Furthermore, these new developments may lead to a better understanding of the pathophysiologic mechanisms underlying SFN in these different disorders as well as, in some cases, an expanded spectrum of affected organs and systems. This article reviews these reported associations, their possible pathophysiologic bases, and the potential resulting management implications.