Practice Parameter and Literature Review of the Usefulness of ...

Practice Parameter: Carpal Tunnel Syndromeclinical findings of thenar muscle weakness and atrophy.Thus, selection of more advanced cases would increase theyield of EDX abnormalities. A report by Buchthal andcolleagues 31 in 1974 illustrated this point because theyreported a 91% incidence of abnormal findings on theneedle EMG examination of the abductor pollicis brevis(APB) muscle in CTS patients. Subsequent studies of needleEMG findings in CTS 243 and the consensus of members ofthe 1991 to 1993 AAEM QA Committee and the AAEMCTS Task Force was that the incidence of abnormal needleEMG findings in the thenar muscles of CTS patients ismuch less than were reported by Buchthal and colleagues 31whose studies were conducted at a national clinical researchcenter.To balance the authority of a publication meeting the 6AAEM CTS LIC in a controlled academic setting with thereality of clinical experience, the 1991 to 1993 QACommittee decided to report data in tables only if themaximum incidence of any EDX abnormality in all the CTSpatients in the study was less than 90%. If over 90% of thepatients with a clinical diagnosis of CTS demonstrate a testabnormality, the results suggest that the patient populationwas heavily screened and, therefore, biased with patientswith advanced CTS. For this reason, the studies of Caseyand LeQuesne 39 and Cioni and colleagues, 47 which met the 6literature classification criteria, were not included in thetable data of the 1993 publication. This convention waseliminated from the current review. Data from all studiesthat met 6 AAEM CTS LIC are displayed in tablesregardless of how high or low the sensitivity and specificityof the test results so readers can draw their own conclusions.The AAEM CTS Task Force identified 2 possible sourcesof investigator bias in the CTS literature: selection bias andobserver bias.Selection bias might increase the incidence of EDX testabnormalities due to inclusion of CTS patients with moresevere CTS than usually encountered in a clinical practice.To address prospectively the issue of selection bias in CTSresearch studies as described above, the AAEM CTS TaskForce developed a set of criteria for the clinical diagnosis ofCTS to provide a more uniform population of CTS patientsfor use in future research studies of the usefulness of EDXstudies to diagnose CTS (see Table 2).Observer bias might increase the incidence of EDX testabnormalities due to the desire of the researcher todocument the usefulness of the EDX test. To addressprospectively the issue of observer bias, Sackett andcolleagues 217 have recommended that clinical researchstudies of diagnostic tests be performed with the physicianperforming and interpreting the diagnostic tests blinded tothe diagnosis of the subject. At the recommendation of theAAN, the AAEM recently endorsed that principle andrecommends that physicians performing and interpreting theEDX test as part of a clinical research study be blinded tothe clinical classification of the research subjects (normal,CTS, disease control).REVIEW OF EDX STUDIESThe identification of the clinical manifestations andoperative treatment for symptoms due to compression of themedian nerve in the carpal tunnel are generally credited toPhalen 198 although there were earlier reports of successfulsurgical treatment of median nerve compression in thecarpal tunnel. 23,37,270,273 In 1953, Kremer published thesalient clinical feature of CTS. 138In 1949, Dawson and Scott 54 reported the reproduciblerecording of nerve action potentials with surface electrodesin arms of healthy human subjects after electric stimulationof the nerves and suggested that the technique may be usefulin detecting nerve damage. In 1956, Simpson 238 reported theobservation that the median motor distal latency wasprolonged across the carpal tunnel in CTS and this wasconfirmed by other investigators: Thomas 252 in 1960 andLambert 141 in 1962. In 1956, Dawson 53 described atechnique for measuring median sensory nerve conductionacross the carpal tunnel. In 1958, Gilliatt and Sears 85demonstrated slow median sensory nerve conduction acrossthe carpal tunnel in patients with CTS. Casey andLeQuesne 39 confirmed the finding of Buchthal andRosenfalck 30 that the median nerve conductionabnormalities in CTS were focal and localized to thesegment of the median nerve in the carpal tunnel. Brown 28confirmed the localization of the median nerve conductionabnormalities in CTS patients to be under the carpalligament with intraoperative NCSs. Other studies haveverified these reports and median sensory and motor NCSshave become the mainstay for the laboratory evaluation ofCTS. 243Over the past 40 years, clinical research efforts have refinedthe techniques of median sensory and motor NCSs acrossthe carpal tunnel to make the tests more sensitive andspecific for the detection of compression of the mediannerve in the carpal tunnel. 110,181 To make the NCSs moresensitive, investigators have developed techniques toexclude the normal segment of the median nerve distal tothe flexor retinaculum of the carpal tunnel, 30,52,59,65,104,143,265compared the speed of median nerve conduction to thespeed of ulnar or radial nerve conduction from the samehand, 31,200,216,220,233,253 performed sequential short segment (1cm) sensory and motor NCSs, 106,132,224 ,226 and compared themedian nerve conduction across the carpal tunnel to mediannerve conduction in the forearm or digit. 131,188,189,236,237S928 CTS Literature Review© 2002 American Association of Electrodiagnostic Medicine