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

Practice Parameter: Carpal Tunnel SyndromeTable 3. Median Motor Nerve Distal Latency in CTS.Author DeLean 57 Jackson andClifford 110 Kimura 130 Padua andcolleagues 188Padua andcolleagues 189 Kuntzer 140 Cioni andcolleagues 47Year 1988 1989 1979 1996 1997* 1994 1989Number ofNormal Hands 80 (43) 38 (38) 122 (61) 40 (36) 70 (70)† 56 (54)(subjects)Normal33 (20 to43 (15 to38 (18 toSubject’s Age:42 (21 to 69)44 (19 to 79) 43 (25 to 70)73)60)68)Mean (range)Number of CTS253 (150) 131 (123) 172 (105) 50 (43) 500 (379) 100 (100)† 375 (370)Hands (patients)CTS SubjectsAge: Mean(range)Technique:ConductionDistance47 (20 to84)6 cm to 8cm53 (21 to 85)8 cmStimulation Site Wrist Wrist48 (20 to78)Anatomicallandmarks3 cmproximal towrist crease45 (23 to 80) 51 (20 to 88) 51 (26 to 85)6 cm to 8 cm‡WristAnatomicallandmarksDistal wristcrease46 (20 to72)Recording Site APB APB APB APB APB APBMinimum HandTemperature32°C 31°C 34°C 31°C 32°C 33°CMedian Motor3.2 ± 0.4 3.18 ± 0.27 3.60 ± 0.363.66 ± 0.38Distal Latency ±3.2 ± 0.4 ms§ms msmsmsSDCriteria forAbnormal ValueMean + 2SDMean + 2 SDMean + 2SDMean + 2 SDMean + 2 SD6 cmWrist3.3 ± 0.5 msMean + 2SDAbnormal Value >4.2 ms >3.71 ms >4.4 ms 3.2 ± 0.4 ms§ >4.5 ms >4.3 msSpecificity of 99% 95%‡ 97.5%98.6% 97.5%97.5% (estimate)Abnormal Value (estimate) (actual) (estimate)(actual) (estimate)Sensitivity of60% 74%‡ 61% 44% 55% 47% 80%Abnormal ValueThe median nerve motor conduction studies cited in Table 3 were performed by fastening surface recording electrodes over the thenar eminence(G1 or E1) and thumb (G2 or E2) and supramaximal stimulation of the median nerve with surface electrodes above the wrist crease. With theseanatomic landmarks, the conduction distance is usually 6 to 8 cm in normal adults. The time (latency) from the stimulus artifact to the initialnegative deflection of the compound muscle action potential (CMAP) was measured in ms and recorded as the median motor distal latency(MDL). Slowing of median motor nerve conduction in the carpal tunnel with nerve injury will result in prolongation of the median MDL. Becausecooling of the nerve fibers and increasing the conduction distance also result in prolongation of the median nerve MDL, it is important that thelimb temperature and the conduction distance be controlled.* 1997 Padua and colleagues paper 189 cites reference population studies performed in the same laboratory in 1996. 188† For each reference subject, only one hand was tested; for each CTS patient, only the most symptomatic hand was tested.‡ Written communication.§ Written communication: the SD of the normal value was misprinted in the 1996 paper, Table 1 (page 50), 3.2 ± 0.8 ms, and should have been 0.4ms. The abnormal value (4.0 ms) was published correctly.Specificity equals the percentage of reference subjects’ hands with normal results and was either “actual” based on analysis of the test data fromthe reference population or an “estimate” based on the statistical distribution of test data from the reference population.Sensitivity equals the percentage of CTS patients’ hands with abnormal results calculated from the test data on the CTS population.APB = Abductor Pollicis Brevis CTS = Carpal Tunnel Syndrome SD = Standard DeviationMuscle & Nerve Supplement X 2002 S933