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Journal of Neurological Sciences (Turkish)
2005, Volume 22, Number 1, Page(s) 015-020
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Evaluation of F-Wave in Carpal Tunnel Syndrome (CTS) and Its Prognostic Value
Mohammad YAZDCHI , Reza KHANDAGHI , Mohammad Ali ARAMI
Department of Neurology, Imam Khomeini Hospital, Tabriz University of Medical Sciences, Tabriz, İran
Summary
Objectives: In this study we have analyzed the effects of focal median nerve injury on F wave. We have determined the F wave parameters in CTS patients and compared the results with corrected normal values for each patient according to his/her stature. Also we evaluated the relationship between F wave and severity of injury.

Patients and methods: The study was conducted on all of the patients referred to Electrophysiology Laboratory of Imam Khomeini Hospital for upper extremity complaints compatible with CTS. Standard electrodiagnostic study was made on all of them bilaterally. According to F wave parameters, patients were divided into three groups, absent F-wave, abnormally prolonged F-wave and normal F-wave. According to electrophysiological testing results, the patients were grouped into mild, moderate or severe CTS.

Results: Absent F wave was presented in 8 hands (7.7%), prolonged latency in 9 hands (8.7%) and normal F wave in 87 of 104 hands (83.7%). the mean F wave latency were statistically different between the CTS patients and the normal values (CI 95%, p<0.0001). Also, the entire F wave latencies were significantly prolonged in the severeely injured group (p=0.0001).

Discussion: F wave determination could show injury to proximal and also severe injury to distal parts of median nerve and especially axonal injury. According to abnormalities of this test the surgical release of nerve for prevention of irreversible changes must be considered. Results of our study supported the adding of F wave parameters study to standardize electrophysiological evaluation of CTS.

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  • Summary
  • Introduction
  • Methods
  • Results
  • Discussion
  • References
  • Introduction
    Carpal tunnel syndrome (CTS) is a common clinical problem and frequently requires surgical therapy. The diagnosis of carpal tunnel syndrome (CTS) is based upon the clinical symptoms and signs (Tinel's sign and phalen's sign) and the absence of objective evidence of median nerve compression proximal to the carpal tunnel 11. The most informative tests for CTS diagnosis are sensory nerve conduction over palm-wrist segment and terminal latency of median nerve. Classic abnormalities in these tests are abnormal sensory conduction over the tested segments and prolonged terminal latency. With more severe CTS cases, Electrodiagnostic study (EDX) usually shows some secondary axonal loss. Axonal injury is reflected in reduced amplitude and area of the CMAP in response to the stimulation at any point along the nerve 3.

    The F-wave is a long latency muscle action potential seen after supramaximal stimulation to a nerve. Although elicitable in a variety of muscles, it is the best obtained in the small foot and hand muscles. It is generally accepted that the F-wave is elicited when the stimulus travels antidromically along the motor fibers and reaches the anterior horn cell at a critical time to depolarize it. The response is then fired down along the axon and causes a minimal contraction of the muscle. Conventionally, ten to twenty F-waves are obtained and the shortest latency F-wave among them is used.

    The normal values can be determined from charts or published data and, in unilateral lesions, the best normal values remain those of the patient's asymptomatic limb. The difference between both sides' shortest latencies should not exceed l ms. The obtained data have been used to determine proximal or distal injuries to nerve. The study of Anastasopoulos showed that median nerve proximal conduction velocity slowing in patients with CTS is restricted to the fibers that distally pass through the carpal tunnel and does not necessarily imply an additional proximal lesion 6.

    F waves are not sensitive in detecting compressive neuropathy 7. If the stimulus is applied distal to the lesion, the F wave latencies may be prolonged, establishing the presence of a lesion, but the result does not indicate the location because of the long length of the nerve included in the conduction pathway 3.

    In this study we analyzed the effects of focal median nerve injury on F wave. We determined the F wave parameters in CTS patients and compared the results with corrected normal values for each patient according to his/her stature. Also we evaluated the relationship between F wave and severity of injury.

  • Top
  • Summary
  • Introduction
  • Methods
  • Results
  • Disscussion
  • References
  • Methods
    The study was conducted on all of the patients referred to Electrophysiology Laboratory of Imam Khomeini Hospital for upper extremity complaints compatible with CTS and were supported with EDX study, since May to November 2003. Some groups of patients were excluded from the study because of : clinical, radiological findings and EDX findings of cervical radiculopathy and every risk factor for neuropathy (i.e. diabetes mellitus, chronic renal failure, connective tissue disorders ) .

    Normal ranges calculated according to Shin J Oh. [Median F wave Latency (msec) = 0.183 height (cm) - 4.81 , 2SD=3.10] 14 and these measures were compared with results of tests on patients. All of the patients had clinical criteria for CTS. Standard electrodiagnostic study was made and using the criteria of the American Association of Electrodiagnostic Medicine (AAEM) 6. All patients were studied bilaterally.

    Two of the following criteria for abnormal values were accepted to identify the patients with CTS;

    1) Antidromic sensory conduction velocity for the wrist-second digit segment less than 48.2 m/s,
    2) The difference between median and ulnar sensory nerve distal latencies with recording from the fourth digit (recording-stimulation distance was kept 14 cm) exceeding 0.5 ms,
    3) Distal motor latency to abductor pollicis brevis muscle greater than 4.2 ms.
    According to F wave parameters, patients were divided into three groups, absent F-wave , abnormally prolonged F-wave and normal F-wave.

    According to following electrophysiological testing results, the patients were grouped into mild, moderate or severe CTS:

    Mild CTS: Prolongation of median distal sensory latency >3.5 ms or relative prolongation of median compared to ulnar distal sensory latencies over identical distances.

    Moderate CTS: Reduced median SNAP amplitude (<50% compared to unaffected side or <25mv) or prolonged median motor distal >4.5 ms.

    Severe CTS: Reduced median CMAP amplitude (<50% compared to unaffected side or <4mv) denervation of median innervated muscles on needle exam.(2)

    The patients data was compared with calculated values for each case using paired t-test, and the relationships between F wave abnormalities and severity of CTS were studied with chi-square test. Examination was done with EMG/NC study apparatus marked Toenniss® (Neuroscreen-plus) with setting as: Sensitivity: 5000Uv Div; Low pass: 5000Hz; High pass: 5Hz; Sweep: 10; Time Base: 10; Type of stimulus: single, Pulse duration: 200ms.

  • Top
  • Summary
  • Introduction
  • Methods
  • Results
  • Disscussion
  • References
  • Results
    On neurological examination, a total of 51 hands (49%) out of 104 hands had positive Tinel’s sign and 43 hands (41.3%) had positive Phalen’s test. In 34 hands (32.7%) CTS were mild, in 56 hands (53.8%) moderate and in 14 hands (13.5%) it was severe.

    Among 55 studied patients, 46 (84%) were female and 9 (16%) were male. The average age was 44.4 years old (range 23-77 years old). Six patients had unilateral and 49 patients had bilateral CTS.

    Absent F wave was presented in 8 hands (7.7%), prolonged latency in 9 hands (8.7%) and normal f wave in 87 of 104 hands (83.7%).

    The mean F wave latency was 27.15±2.9 msec. The normal mean F wave latency (matched case by case) calculated around 24.36±1.4 msec. The mean F wave latency were statistically different between the CTS patients and the normal values (CI 95%, p<0.0001). There was significant mean F wave latency in hands with mild CTS was 25.66±1.56 msec and the normal mean F wave for this group was 24.6±1.3 msec. These data for moderate CTS group was 27.13±2.1 msec and 24.1±1.5 msec.

    All of the F wave latencies were significantly prolonged in the severely injured group (32.2±4.35 msec, normal mean calculated for this group was 23.8±1.5 msec) compared to the moderate and mild injuries (p=0.0001, Fig. 1).


    Büyütmek İçin Tıklayın
    Fig 1: correlation between mean F wave latency and severity of injury.

    The F wave persistence in patients with severe (axonal) damage was significantly lower than that in patients with the moderate and mild demyelinating types (P=0.003, Fig-2).


    Büyütmek İçin Tıklayın
    Fig 2: correlation between severity of injury and F wave persistence

  • Top
  • Summary
  • Introduction
  • Methods
  • Results
  • Disscussion
  • References
  • Discussion
    To recommendation of proper therapeutic methods to patients and their physicians and also to determine surgical indications, information about the type of affected nerve fibers of the median nerve and injury severity are important. The results say that F wave has significant correlation with axonal injury that we called "severe" injury in this study.

    In CTS, we can determine the severity and duration of nerve compression and the degree of demyelination and axonal degeneration by comparing responses evoked by stimulation proximal and distal to lesion site 12.

    Johnson et al. reported that conduction block is a sign of demyelinating injury, and this finding suggests that a conservative treatment such as splinting or steroid injections could be a proper method for patient managing, but axonal loss (with prominent decrease in CMAP amplitude) is a clue to necessary surgical release of nerve 8.

    The results of Fisher MA et al study support differing effects of demyelinating and axonal injury on F-waves, and suggest physiological compensation in those hands with the more pronounced neuropathic dysfunction 5. Özge and colleague concluded that F wave determination, as a simple and valuable method, allows the discrimination between demyelinating injury and axonal degeneration and increases the diagnostic yield in CTS. 13.

    Knutzer 9 concluded that the importance of median F wave abnormalities of the patients in early stage of CTS, was not known, but Eisan et al. 4 suggested that F wave latencies were useful in differentiating between distal and proximal entrapments.

    However, in our study, after exclusion of all cases with proximal lesions and neuropathic problems, we observed a high ratio of F wave abnormalities (16.4%).

    Results of our study supported the adding of F wave parameters study to standardize electrophysiological evaluation of CTS. It helps for distinguishing CTS severity. Also, according the criteria that we used for definition of severity of injury (including CMAP amplitude for "severe" cases), we concluded that F wave prolongation shows axonal injury.

    Our findings partly support the results of Leffler et al. as to the association between the amplitude of CMAP and F wave persistence 10.

    As a conclusion, F wave determination could show injury to proximal and also severe injury to distal parts of median nerve and especially axonal injury. According to abnormalities of this test and other symptoms and signs, the surgical release of nerve for prevention of irreversible changes could be considered.

  • Top
  • Summary
  • Introduction
  • Methods
  • Results
  • Discussion
  • References
  • References

    1) Anastasopoulos D, Chroni E. Effect of carpal tunnel syndrome on median nerve proximal conduction estimated by F-waves. J Clin Neurophysiol. 1997 Jan;14 (1):63-7. [MedLine-Abstract]

    2) Aurora SK, Ahmad BK, Aurora TK. Silent Period Abnormalities in Carpal Tunnel Syndrome. Muscle Nerve 1998;21:1213-1215. [MedLine-Abstract]

    3) de Araujo MP. Electrodiagnosis in compression neuropathies of the upper extremities. Orthop Clin North Am 1996;27 (2):237- 44. [MedLine-Abstract]

    4) Eisen A, Schomer D, Melmed C. The application of F-wave measurements in the differentiation of proximal and distal upper limb entrapments. Neurology 1977;27(7):662-8. [MedLine-Abstract]

    5) Fisher MA, Hoffen B. F wave analysis in patients with carpal tunnel syndrome. Electromyogr Clin Neurophysiol 1997;37(1):27-31. [MedLine-Abstract]

    6) Jablecki CK, Andary MT, So YT, Wilkins DE, Williams FH. American Academy of Electrodiagnostic Medicine Quality Assurance Committee. Literature review of the usefulness of nerve conduction studies and electromyography for the evaluation of patients with Carpal Tunnel Syndrome. Muscle Nerve, 1993;16:1392-1414. [MedLine-Abstract]

    7) Jablecki CK, Andary MT, Floeter MK, Miller RG, Quartly CA, Vennix MJ, Wilson JR; American Association of Electrodiagnostic Medicine; American Academy of Neurology; American Academy of Physical Medicine and Rehabilitation. Practice parameter: Electrodiagnostic studies in carpal tunnel syndrome. Neurology 2002; 58: 1589-1592. [MedLine]

    8) Johnson EW. Should immediate surgery be done for carpal tunnel syndrome? Muscle Nerve 1995;18:658-9. [MedLine]

    9) Kuntzer T. Carpal tunnel syndrome in 100 patients: sensitivity, specificity of multi-neurophysiological procedures and estimation of axonal loss of motor, sensory and sympathetic median nerve fibers. J Neurol Sci 1994;127(2):221-9. [MedLine-Abstract]

    10) Leffler CT, Gozani SN, Cros D. Median neuropathy at the wrist: diagnostic utility of clinical findings and an automated electro-diagnostic device. J Occup Environ Med 2000;42(4):398-409. [MedLine-Abstract]

    11) Novak CB, Mackinnon SE, Brownlee R, Kelly L. Provocative sensory testing in carpal tunnel syndrome. Hand Surg (Br) 1992;17:204-8. [MedLine-Abstract]

    12) Olney RK, Miller RG. Conduction block in compression neuropathy: recognition and quantification. Muscle Nerve, 1984;7:662-7 [MedLine-Abstract]

    13) Ozge A, Comelekoglu U, Tataroglu C, Yalcinkaya DE, Akyatan MN. Subtypes of carpal tunnel syndrome: median nerve F wave parameters. Clin Neurol Neurosurg. 2002 ;104(4):322-7. [MedLine-Abstract]

    14) Oh SJ. Clinical Electromyography, Nerve Conduction Studies. 3rd ed. Lippincott-Williams and Wilkins. 2003; p 88.

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  • References
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