Citations

Background: The normal limits of nerve conduction studies are commonly determined by testing healthy subjects. However, in comprehensive real-life nerve conduction electrodiagnostic (EDX) evaluations, multiple nerves are tested, including normal nerves, for purposes of comparison with abnormal ones. Objective: This study aims to evaluate the average values of normal nerve conduction studies in a large population and examined the influence of age and sex. Methods: EDX parameters were extracted from an electronic database of studies performed from May 2016 to February 2022. Established normal values were used to determine the classification of a nerve study as normal. Results: We identified 10,648 EDX reports with 5077 normally interpreted nerve conduction studies (47.6%) of which 57% ( n = 2890) were for females. The median age of studies with no abnormalities was 45.1 years (range < 1 to 92) overall and 42.5 years (range: 0.16 –89.5 years) for males and 47.5 years (range:<1 –91.7) for females. Correlations between age and amplitude, latency, and velocity ( p < 0.001) were observed in most nerves. Amplitude correlated negatively with age in adults in all nerves with a mean of –0.44 (range: –0.24 to –0.62). However, in the pediatric population (age < 18 years), amplitude as well as velocity increased significantly with age. In the adult cohort, sex differences were noted, where females had higher mean sensory nerve action potentials in ulnar, median, and radial evaluations ( p < 0.001). In older patients (aged > 70 years) with normally interpreted EDX studies (845 records of 528 patients), sural responses were present in 97%. Conclusions: This real-life study confirms that advanced aging is associated with decreased nerve conduction amplitudes, increased latency, and the slowing of conduction velocity. The findings also indicate higher sensory amplitudes and conduction velocities in females. Sural nerve responses were identified in most adults over age 70.

AbstractIntroduction/AimsImmune‐mediated necrotizing myopathy (IMNM) is considered a rare subtype of the immune‐mediated myopathies, but its incidence and prevalence are unknown. In this study we aimed to determine the incidence and prevalence of IMNM among adults in Olmsted County, Minnesota.MethodsWe identified adult patients with IMNM, as defined by the 2016 European Neuromuscular Centre diagnostic criteria, among residents of Olmsted County, Minnesota over a 20‐year period.ResultsSeven patients fulfilled the inclusion criteria. Six patients were tested for IMNM antibodies: four were anti–3‐hydroxy‐3‐methylglutaryl‐coenzyme A reductase (HMGCR) positive, one was anti–signal recognition particle positive, and one was seronegative. The incidence of IMNM during 2010‐2019 was 8.3 per million person‐years. The prevalence of IMNM in 2010 was 1.85 per 100 000 people at least 50 years of age. Median age at symptom onset was 64 (range, 52‐86) years and median time from symptom onset to diagnosis was 3 (range, <1 to 156) months. Statin use among anti‐HMGCR IMNM patients, but not the entire IMNM cohort, was higher than in controls (P = .024). Two IMNM patients developed cancers. The incidence of malignancy in IMNM was not higher than that of the general population. Treatment outcome was favorable in all patients except for one patient with delayed treatment and another with insufficient therapy. Among three deceased patients, one died of cancer and another died of IMNM‐related cardiorespiratory complications.DiscussionIMNM is a rare disease. Its prevalence is one tenth that of inclusion‐body myositis in Olmsted County, Minnesota. IMNM patients in our cohort were not at higher risk for developing cancer.