Abstract
Latency differences (>0.5 ms) of median and ulnar sensory action potentials (mSAP and uSAP) at the wrist evoked by ring finger stimulation are considered a sensitive and specific test for diagnosis of carpal tunnel syndrome (CTS). In this study, we aimed to assess the practical usefulness of the ring finger test (RFT) in routine electromyography (EMG) examinations. We investigated 2 series of patients: in the first prospective series we considered 300 hands affected by only mild CTS; in the second series we examined retrospectively the EMG charts of 961 hands affected only by CTS but not selected for severity or duration of symptoms. In the first series we found pathological RFT scores in 87% of cases, and pathological RFT or mSAP latency results in 92%. In the second series, pathological RFT scores were found only in 55% of cases, while in 20% where mSAP failed, a volume conducted uSAP had been erroneously interpreted as arising from the median nerve. RFT sensitivity tested in routine EMG examinations of unselected hands affected by CTS drops considerably. Fingers innervated by one only nerve, such as the index and the little fingers, must also be investigated to increase the diagnostic value of RFT.
Sommario
La differenza (>0.5 ms) tra le latenze distali dei potenziali sensitivi di mediano e ulnare (mSAP e uSAP) registrati al polso ed evocati per stimolazione al quarto dito (ring finger test, RTF) viene considerato un test sensibile e specifico per la diagnosi di sindrome del tunnel carpale (CTS). Sono state studiate 2 serie di pazienti: nella prima serie prospettica abbiamo esaminato 300 mani affette da CTS lieve, in cui mSAP e uSAP dopo stimolazione al quarto dito potevano essere chiaramente differenziati. Il RFT era patologico nell'87%. Considerando insieme il risultato del RFT e il valore assoluto della latenza distale del mSAP dal quarto dito, almeno uno dei test era patologico nel 92% dei casi. Nella seconda serie sono stati esaminati retrospettivamente i referti EMG di 961 mani non selezionate affette esclusivamente da CTS. Attraverso il solo RFT solo il 55% delle diagnosi sarebbero state classificate correttamente, perchè in 20% un uSAP volume condotto era stato erroneamente interpretato come proveniente dal mediano. Dita innervate da un solo nervo come il secondo dito ed it quinto dito devono essere esaminate per aumentare il valore diagnostico del RFT in esami di routine.
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Capone, L., Pentore, R., Schönhuber, R. et al. Pitfalls in using the ring finger test alone for the diagnosis of carpal tunnel syndrome. Ital J Neuro Sci 19, 387–390 (1998). https://doi.org/10.1007/BF02341788
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DOI: https://doi.org/10.1007/BF02341788