Diagnostic characteristics of nerve conduction study parameters for vasculitic neuropathy

Abstract

Introduction/aims In vasculitic neuropathy (VN), a 50% side‐to‐side difference in the amplitude of compound muscle action potentials and sensory nerve action potentials is considered meaningful, but unequivocal evidence is lacking. The aim of this study is to characterize electrodiagnostic features that best distinguish VN from other axonal polyneuropathies. Methods We conducted a case–control study between January 2000 and April 2021. We reviewed the records of patients with VN who had bilateral nerve conduction studies (NCS) and evaluated different electrodiagnostic models to help distinguish VN from non‐inflammatory axonal polyneuropathies. Results We identified 82 cases, and 174 controls with non‐inflammatory axonal neuropathies. The amplitude percent difference Z‐score model showed the best discriminatory capability between cases and controls (area under the curve [AUC] 0.87; 95% confidence interval [CI] 0.82, 0.93), and the number of nerves tested did not significantly influence the model. Individually, the ulnar motor nerve (AUC 0.86; 95% CI 0.77, 0.94) and median motor nerve (AUC 0.85; 95% CI 0.77, 0.94) showed the best discriminatory capability. A 50% amplitude difference between at least two bilateral nerves, either in the upper (AUC 0.85; 95% CI 0.77, 0.93) or lower (AUC 0.79; 95% CI 0.71, 0.87) extremity showed good discriminatory threshold for detecting VN. Discussion The best electrodiagnostic criteria for VN utilizes z‐scores of percent differences in nerve amplitudes, but this approach may be difficult to implement at the bedside. Alternately, a 50% amplitude difference in at least two nerves is a reasonable approximation.

Revisiting the compound muscle action potential (CMAP)

“…It is not simple to define a cut-off value for a “physiological” change of CMAP amplitude from one test to another: possibly, a value of about 30 % should be considered acceptable in the upper extremity. In addition to the above studies, other studies of the lower limb ( Davalos et al, 2023 , Kim et al, 2022 ) suggest that 50 % may be acceptable. To optimize CMAP reproducibility and minimize variability, we reiterate the recommendation of Hodes et al ( section 6.8 ) that it is essential to adjust the E1 position in order to obtain the maximum CMAP amplitude response ( Hodes et al, 1948 ).…”

Serial electrodiagnostic testing: Utility and indications in adult neurological disorders

“…EDX findings that may favor disease mimickers over CIDP include disproportionate distal latency prolongation with reduced terminal latency index (anti-myelinassociated glycoprotein neuropathy), 63 uniform velocity slowing with lack of conduction block or temporal dispersion (Charcot-Marie-Tooth disease type 1), 64 more uniform slowing with advanced axonal involvement and/or relatively preserved distal latencies (POEMS [polyneuropathy, organomegaly, endocrinopathy, M-protein, skin changes] syndrome), 65 and ≥50% asymmetry of median or ulnar motor amplitudes (vasculitic multiple mononeuropathy). 66 Predicting likelihood of relapse Serial EDX testing (baseline and post-intravenous immunoglobulin…”

“…In addition, misdiagnosis and overdiagnosis of CIDP based on EDX findings are both significant problems, 62 and serial testing is worthwhile in cases of diagnostic uncertainty, especially when the first study is of questionable technical and interpretive quality. EDX findings that may favor disease mimickers over CIDP include disproportionate distal latency prolongation with reduced terminal latency index (anti‐myelin‐associated glycoprotein neuropathy), 63 uniform velocity slowing with lack of conduction block or temporal dispersion (Charcot–Marie–Tooth disease type 1), 64 more uniform slowing with advanced axonal involvement and/or relatively preserved distal latencies (POEMS [polyneuropathy, organomegaly, endocrinopathy, M‐protein, skin changes] syndrome), 65 and ≥50% asymmetry of median or ulnar motor amplitudes (vasculitic multiple mononeuropathy) 66 …”

Electrodiagnostic studies and new diagnostic modalities for evaluation of peripheral nerve disorders

“…186 Sideto-side asymmetry of NCS is a feature in one half to two thirds of patients, with sensitivity 33%-53% and specificity 67%-98% when compared to non-inflammatory axonal neuropathies. 187 Imaging is not part of the routine diagnostic workup for suspected VN. However, there are a small number of studies to suggest it may have diagnostic utility.…”

“…The most common electrodiagnostic findings are axonal sensorimotor polyneuropathy and mononeuritis multiplex patterns 186 . Side‐to‐side asymmetry of NCS is a feature in one half to two thirds of patients, with sensitivity 33%–53% and specificity 67%–98% when compared to non‐inflammatory axonal neuropathies 187 …”