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The Italian Journal of Neurological Sciences

, Volume 19, Issue 6, pp 387–390 | Cite as

Pitfalls in using the ring finger test alone for the diagnosis of carpal tunnel syndrome

  • L. Capone
  • R. Pentore
  • R. Schönhuber
  • C. Lunazzi
Short Communication

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.

Key words

Carpal tunnel syndrome Ring finger test Pitfalls 

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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References

  1. 1.
    AAEM Quality Assurance Committee, Charles KJ, Michael TA, Yuen T, Dennis EW, Faren HW (1993) Literature review of the usefulness of nerve conduction studies and electromyography for the evaluation of patients with carpal tunnel syndrome. Muscle Nerve 16:1392–1414Google Scholar
  2. 2.
    Kimura J (1979) The carpal tunnel syndrome: Localization of conduction abnormalities within the distal segment of the median nerve. Brain 102:619–635PubMedGoogle Scholar
  3. 3.
    Jackson D, Clifford JC (1989) Electrodiagnosis of mild carpal tunnel syndrome. Arch Phys Med Rehabil 70(3):199–204PubMedGoogle Scholar
  4. 4.
    Cioni R, Passero S, Paradiso C, Giannini F, Battistini N, Rushworth G (1989) Diagnostic specificity of sensory and motor nerve conduction variables in early detection of carpal tunnel syndrome. J Neurol 236(4):208–236.CrossRefPubMedGoogle Scholar
  5. 5.
    Jackson D, Cifford JC (1989) Electrodiagnosis of mild carpal tunnel syndrome. Arch Phys Med Rehabil 70(3):199–204PubMedGoogle Scholar
  6. 6.
    DeLean J (1988) Transcarpal median sensory conduction: detection of latent abnormalities in mild carpal tunnel syndrome. Can J Neurol Sci 15(4):388–393Google Scholar
  7. 7.
    Johnson EW, Sipsky M, Lammertse T (1987) Median and radial sensory latencies to digit. I: Normal values and usefulness in carpal tunnel syndrome. Arch Phys Med Rehabil 68(3):140–141PubMedGoogle Scholar
  8. 8.
    Lauritzen M, Liguori R, Trojaborg W (1991) Orthodromic sensory conduction along the ring finger in normal subjects and in patients with a carpal tunnel syndrome. Electroencephalogr Clin Neurophysiol 81(1):18–23PubMedGoogle Scholar
  9. 9.
    Charles N, Vial C, Chauplannaz G, Bady B (1990) Clinical validation of antidromic stimulation of the ring finger in early electrodiagnosis of mild carpal tunnel syndrome. Electroencephalogr Clin Neurophysiol 76(2):142–147PubMedGoogle Scholar
  10. 10.
    Carroll G (1987) Comparison of median and radial nerve sensory latencies in the electrophysiological diagnosis of carpal tunnel syndrome. Electroencephalogr Clin Neurophysiol 68:101–106PubMedGoogle Scholar
  11. 11.
    White JC, Hansen SR, Johnson RK (1988) A comparison of EMG procedures in the carpal tunnel syndrome with clinical EMG correlation. Muscle Nerve 11(11):1177–1182CrossRefPubMedGoogle Scholar
  12. 12.
    Uncini A, Lange DJ, Soomon M, Soliven B, Meer J, Lovelace RE (1989) Ring finger test in carpal tunnel syndrome: A comparative study of diagnostic utility. Muscle Nerve 12(9):735–741CrossRefPubMedGoogle Scholar
  13. 13.
    Uncini A, Di Muzio A, Awad G, Manente G, Tafuro M, Gambi D (1993) Sensitivity of three median-to-ulnar comparative tests in diagnosis of mild carpal tunnel syndrome. Muscle Nerve 16:1366–1373PubMedGoogle Scholar
  14. 14.
    Kimura J (1989) Electrodiagnosis in diseases of nerve and muscle: principles and practice, 2nd edn. F.A. Davis, PhiladelphiaGoogle Scholar
  15. 15.
    Seror P (1996) The axonal carpal tunnel syndrome. Electroencephalogr Clin Neurophysiol 101:197–200CrossRefPubMedGoogle Scholar
  16. 16.
    Padua L, Lo Monaco M, Valente EM, Tonali PA (1996) A useful electrophysiologic parameter for diagnosis of carpal tunnel syndrome. Muscle Nerve 19:48–53CrossRefPubMedGoogle Scholar

Copyright information

© Springer-Verlag 1998

Authors and Affiliations

  • L. Capone
    • 1
  • R. Pentore
    • 1
  • R. Schönhuber
    • 1
  • C. Lunazzi
    • 2
  1. 1.Department of NeurologyRegional General HospitalBolzanoItaly
  2. 2.Department of NeurologyUniversity of ModenaModenaItaly

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