Background/Purpose: Small fibre neuropathy (SFN) is a peripheral neuropathy characterized by neuropathic pain associated with normal routine nerve conduction study but rarefaction of intraepidermal nerve fibres (IEFN). Primary Sjögren Syndrome (pSS) is one of the many aetiology of SFN. To compare phenotype of SFN in pSS, transthyretin (TTR) familial amyloidosis and idiopathic SFN. To describe evolution of SFN in pSS.

Methods: All patients referred since 2012 with a skin biopsy-proven SFN associated with either pSS (ACR/EULAR 2016 criteria), TTR amyloidosis or idiopathic were included in this monocentric retrospective study. Diagnosis of SFN was confirmed by normal nerve conduction study and abnormal lower limb skin biopsies. All patients undergo standardized diagnosis procedures during an outpatient day-clinic, pSS patients were further followed and undergo a second evaluation. Characteristics of SFN were compared between 3 groups: pSS, TTR-amyloidosis and idiopathic. Outcome of pSS associated SFN was analysed.

Results: We included 15 patients with pSS (13 (86.7 %) women, median age: 55 years [IQR:47.5-66.5], 7 (46.7%) anti-SSA positive, 12 (80%) focus score ≥1), 17 with TTR-amyloidosis (7 (41.2%) women, median age: 47 years [35-56]) and 11 with idiopathic SFN (7 (63.6%) women, median age: 47 years [36-56.5]). Patients with pSS had a median ESSDAI of 5 [5-8]. One had monoclonal gammopathy (6.7%), 5/13 (38.5%) rheumatoid factor, 2/13 (15.4%) hypergammaglobulinemia and none had cryoglobulin. Time to diagnosis SFN was significantly higher for pSS (21 months [9-54]) and idiopathic group (35 months [11.5-65]) than for TTR group (6 months [0-15]). Clinical presentation was length dependent in 2 (13.3%) pSS patients compared to 10 (58.8%) in TTR amyloidosis (p= 0.01) and 2 (18.2%) in idiopathic group (p=1). A “patchy” presentation (defined as asymmetrical and/or proximal symptoms involving limb, trunk and/or face), was significantly more frequent in pSS than in TTR amyloidosis (7 (46.7%) vs. 1 (5.9%); p = 0.01). This more frequent non-length dependent course was confirmed by skin biopsies (IEFN at proximal site < IEFN at distal site) in 7/14 (50%) pSS patients compared to 1 (9.1%) in idiopathic (p=0.04) and 2/15 (13.3%) in TTR groups (p=0.05). Lauria score was significantly higher in pSS than in TTR, (5 [4-7.5] vs. 2 [2-5], p = 0.007), mainly due to items of sicca symptoms (n=14/15) and peripheral limb pain (n=13/15). Ten patients with pSS have been reassessed with a median follow up of 37 months [20.5-56.3]. At reassessment, the Lauria score did not significantly differ (6.5 [5.3-7.8], p=0.48) from baseline, patchy presentation was still predominant (50%). Patients did not evolve through large fibre neuropathy, except one patient who had received a neurotoxic chemotherapy by platin for ovarian cancer, between the 2 evaluations.

Conclusion: Compared to other causes of SFN, in pSS SNF was characterized by a more frequent non-length dependent and patchy presentation and a higher Lauria score. After a median follow-up of >3 years, SFN in pSS did not evolve through large fibre neuropathy, which supports the hypothesis that it is related to a specific mechanism and does not represent the beginning of an axonal neuropathy like it is for TTR amyloidosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/how-phenotype-of-the-small-fibre-neuropathy-in-primary-sjogren-syndrome-differs-from-others-causes-of-small-fibre-neuropathy/