Clinical, histologic, and immunologic signatures of Small Fiber Neuropathy in Systemic Lupus Erythematosus.

Background And Objectives: Systemic Lupus Erythematosus (SLE) often causes damage to small nerve fibers, leading to distressing painful and autonomic symptoms. Despite this, Small Fiber Neuropathy (SFN) remains an underrecognized complication for SLE patients. In this cross-sectional study, we aimed to assess SFN in patients with SLE and to explore its correlations with immunologic disease features and clinical manifestations.

Methods: We recruited 50 SLE patients (1 male to 12.5 females, aged 20-80 years) reporting painful disturbances. We conducted a comprehensive clinical and neurophysiological evaluation, using Nerve Conduction Studies and Quantitative Sensory Testing. Additionally, we carried out an extensive laboratory assessment of disease-related serological parameters. We also performed a thorough skin biopsy analysis, investigating somatic and autonomic innervation while detecting complement and inflammatory cell infiltrates within the skin.

Results: Out of 50 patients, 19 were diagnosed with SFN, primarily characterized by a non-length-dependent distribution; 7 had a mixed neuropathy, with both large and small fiber involvement. Patients with SFN were younger than patients with a mixed neuropathy (p = .0143); furthermore, they were more likely to have a history of hypocomplementemia (p = .0058) and to be treated with cyclosporine A (p = .0053) compared to patients without neuropathy. However, there were no significant differences in painful and autonomic symptoms between patients with and without SFN.

Discussion: This study highlights the relevant frequency of SFN with a non-length-dependent distribution among SLE patients experiencing painful symptoms. Indeed, SFN emerges as an early manifestation of SLE-related neuropathy and is closely associated with hypocomplementemia, suggesting a potential pathogenic role of the complement system. Moreover, SFN may be influenced by disease-modifying therapies. However, the precise role of SFN in shaping painful and autonomic symptoms in patients with SLE remains to be fully elucidated.