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

Practice Parameter: Carpal Tunnel Syndromeversus 47%, but with lower specificity, 89% versus 99%(Table 7 and Table 3). The latter results suggest that if thecriteria for an abnormal RL were adjusted for comparablespecificity, that the increased incidence of abnormalitieswould fall. Evidence to support this conclusion is found inthe study by Trojaborg, 253 which met 5 of the 6 AAEM CTSLIC. Trojaborg 253 noted a lower incidence of abnormal RLvalues (48%) compared to abnormal distal latency values(60%) in CTS patients with comparable specificity and thatthe RL was normal in CTS patients with normal medianmotor distal latencies. The interested reader is also referredto studies of median motor nerve RL previously reviewed inthe 1993 AAEM CTS Literature Review. 66,116,137,204Median Nerve Terminal Latency Index. Simovic andWeinberg 236,237 provide a summary of the reported studieson the usefulness of the median motor TLI to diagnose CTS.In 1979, Shahani described the potential usefulness of theTLI ratio to diagnose CTS. In 1988, Lissens reported similarfindings in the Dutch literature. The TLI is calculated fromthe conventional median motor NCS measurements thatadjusts the median motor distal latency for the terminalmotor conduction distance and the proximal median motornerve CV. The TLI is calculated as follows: terminalconduction distance / [proximal CV × distal latency]. Theratio decreases as the conduction time increases across thecarpal tunnel.Table 8 presents the results of 2 studies of the TLI that met 6AAEM CTS LIC. The study by Simovic and Weinberg 237concluded that 81.5% of CTS patients demonstrate a TLIless than 0.34. However, Donahue and colleagues 60 notedthat the presence of the Martin-Gruber anastomosis in CTSpatients could create an artificially high median motorforearm CV measurement. The study by Kuntzer 140 notedthat 10% of the control group and 7% of the CTS groupshowed a median-to-ulnar crossover. Kuntzer 140 excludedthose normal subjects and CTS patients from his analysis ofthe value of the TLI to identify CTS and noted that only50% of the CTS group showed a TLI less than 0.34 with aspecificity of 91%. Simovic and Weinberg 237 provided asummary of the published normative data on 242 hands andnoted that only 6 had a TLI under 0.34 to yield a specificityof 97.5%. These interesting findings need to be confirmed inother laboratories to determine the usefulness of the TLI todiagnose CTS.Comparison of Median Motor Nerve Conduction to UlnarMotor Nerve Conduction in the Same Limb. There are 3different published methods to confirm the diagnosis ofCTS by calculating the difference between the median andulnar nerve distal motor latencies: the median-thenar toulnar-hypothenar latency difference (THLD), 167 the medianthenarto ulnar-thenar latency difference (TTLD), 220 and themedian-lumbrical to ulnar-interossei latency difference(LILD). 146 These studies approach the sensitivity of medianTable 7. Median Motor Nerve RL in CTS.Author Kuntzer 140Year 1994Number of Normal Hands(subjects)70 (70)*Normal Subject’s Age: Mean(range)43 (25 to 70)Number CTS hands(patients)100 (100)*CTS Subject Age 51 (26 to 85)Technique: ConductionDistanceAnatomical landmarksStimulation SiteDistal wrist creaseRecording SiteMinimum HandTemperatureNormal RL ± SDCriteria for Abnormal ValueAbnormal ValuesSpecificity of AbnormalValueSensitivity of AbnormalValueAPB32°C1.96 ± 0.32 msMean + 2 SD>2.6 ms88.5% (actual)64%* For each reference subject, only 1 hand was tested: for each CTSpatient, only the most symptomatic hand was tested.Specificity equals the percentage of reference subjects’ hands withnormal results and was either “actual” based on analysis of the testdata from the reference population or an “estimate” based on thestatistical distribution of test data from the reference population.Sensitivity equals the percentage of CTS patients’ hands withabnormal results calculated from the test data on the CTSpopulation.APB = Abductor Pollicis Brevis CTS = Carpal Tunnel SyndromeRL = Residual Latency SD = Standard Deviationsensory NCSs in the diagnosis of CTS and may also be usefulin localizing median nerve pathology to the wrist (1) when themedian sensory response is absent and (2) when CTS occursin the presence of a polyneuropathy. 220,253Median-Thenar to Ulnar-Hypothenar Latency Difference.The THLD method is straightforward and calculates thedifference (THLD) between (1) the distal latency of theCMAP recorded over the APB with median nervestimulation at the wrist (thenar latency) and (2) the distallatency of the CMAP recorded over the abductor digitiminimi (ADM) with ulnar nerve stimulation at the wrist(hypothenar latency). 167,220 There are no studies of thismethod that meet all 6 AAEM CTS LIC. In a study that met5 of the 6 AAEM CTS LIC, Sander 220 noted the sensitivityS936 CTS Literature Review© 2002 American Association of Electrodiagnostic Medicine