Initial validation of the Mass. General Neuropathy Exam Tool (MAGNET) for evaluation of distal small‐fiber neuropathy

Abstract

AbstractIntroduction/AimsDiagnosis of small‐fiber neuropathy (SFN) is hampered by its subjective symptoms and signs. Confirmatory testing is insufficiently available and expensive, so predictive examinations have value. However, few support the 2020 SFN consensus‐case‐definition requirements or were validated for non‐diabetes neuropathies. Thus we developed the Massachusetts General Hospital Neuropathy Exam Tool (MAGNET) and measured diagnostic performance in 160 symptomatic patients evaluated for length‐dependent SFN from any cause and 37 healthy volunteers.MethodsWe compared prevalences of abnormalities (vital signs, pupil responses, lower‐limb appearance, pin, light touch, vibration and position sensitivity, great‐toe strength, muscle stretch reflexes), and validated diagnostic performance against objective SFN tests: lower‐leg skin‐biopsy epidermal neurite densities and autonomic function testing (AFT). Sensitivity/specificity, feasibility, test–retest and inter‐rater reliability, and convergence with the Utah Early Neuropathy Scale were calculated.ResultsPatients’ ages averaged 48.5 ± 14.7 years and 70.6% were female. Causes of neuropathy varied, remaining unknown in 59.5%. Among the 46 with abnormal skin biopsies, the most prevalent abnormality was reduced pin sharpness at the toes (71.7%). Inter‐rater reliability, test–retest reliability, and convergent validity excelled (range = 91.3–95.6%). Receiver operating characteristics comparing all symptomatic patients versus healthy controls indicated that a MAGNET threshold score of 14 maximized predictive accuracy for skin biopsies (0.74) and a 30 cut‐off maximized accuracy for predicting AFT (0.60). Analyzing patients with any abnormal neuropathy‐test results identified areas‐under‐the‐curves of 0.87–0.89 for predicting a diagnostic result, accuracy = 0.80–0.89, and Youden's index = 0.62. Overall, MAGNET was 80%–85% accurate for stratifying patients with abnormal versus normal neuropathy test results.DiscussionMAGNET quickly generates research‐quality metrics during clinical examinations.