An algorithm for the diagnosis of peripheral nervous system involvement in antineutrophil cytoplasmic antibody associated vasculitides (ANCA-associated vasculitis)

Peripheral nervous system (PNS) involvement in antineutrophil cytoplasmic antibody associated vasculitides (ANCA-associated vasculitis) occurs with varying frequency depending on the nosological form. Timely diagnosis and differentiation of PNS involvement phenotypes across different nosological forms are critical for selecting the optimal therapeutic approach. Objective: to develop a diagnostic algorithm for peripheral nervous system (PNS) involvement in ANCA-associated vasculitides and to identify the clinical and electrophysiological characteristics of PNS involvement in granulomatosis with polyangiitis (GPA), eosinophilic granulomatosis with polyangiitis (EGPA) and microscopic polyangiitis (MPA). Material and methods. A retrospective-prospective, single-centre cohort study was conducted involving 56 patients with confirmed ANCA-associated vasculitis: GPA (n=22), EGPA (n=21) and MPA (n=13). Clinical neurological examinations were performed using the NIS-LL/UL scales (a scale for the quantitative assessment of neurological deficits in the upper and lower limbs), the DN4 (a diagnostic questionnaire for neuropathic pain), TQOL (Total Quality of Life), electroneuromyography (ENMG) with calculation of asymmetry in parameters, ANCA serological testing, and calculation of the BVAS (Birmingham Vasculitis Activity Score) and VDI (Vasculitis Damage Index). Results. PNS involvement was detected in 100% of the patients examined. GPA was characterized by upper respiratory tract involvement (100%) and hearing loss (59.1%; p=0.002 for paired comparisons versus EGPA and p=0.001 versus MPA), PR3-ANCA (86.4%), a maximum VDI score of 5.50 (5.00–6.75; p=0.010 in a pairwise comparison with MPA), the lowest prevalence of small-fibre neuropathy as determined by quantitative sensory testing (QST; 4.5%) and a reduction in the M-response amplitude of the left median nerve compared with the control group (p<0.001). For EGPA – bronchial asthma (85.7%; paired p<0.001 versus GPA and MPA), ANCA-negativity (47.6%), the highest prevalence of small-fibre neuropathy (57.1%; p=0.001 in pairwise comparisons versus GPA) and the most pronounced changes in temperature thresh-olds according to QST data: an increase in heat sensitivity thresholds and a decrease in cold sensitivity thresholds in dermatomes L5 and S1 compared with the control group (p=0.006 and p=0.001). For MPA – renal involvement (92.3%; paired p=0.017 versus EGPA), the highest proportion of multiple mononeuropathy (53.8% versus 18.2% and 19.0%) and complaints of burning (46.2%), a minimum VDI of 2.00 [2.00; 4.00] and the greatest increase in residual latency of the peroneal nerve compared with the control group (p=0.005). Small-fibre neuropathy in MPA was detected in 30.8% of patients. Asymmetry in EMG parameters >50% was recorded with comparable frequency across all groups (72.7; 71.4 and 76.9%; p=0.909). No differences were found between patient groups in terms of quantitative ENMG and QST parameters (all p>0.05). ANCA-associated vasculitides exhibit specific phenotypes of organ involvement and PNS damage, differing in the nature of the neuropathy and the electrophysiological profile. Based on the data obtained, a multi-stage diagnostic algorithm has been developed, enabling the differentiation of nosological forms and the detection of PNS involvement at the subclinical stage. Conclusion. The multi-stage diagnostic algorithm that has been developed makes it possible to differentiate between forms of ANCA-associated vasculitis based on the nature of the PNS involvement and to detect neuropathy at the subclinical stage.