Correlation of Ultrasound and Electrodiagnostic Testing with Severity of Carpal Tunnel Syndrome
Georgios N. Panagopoulos, MD; Tiffany Wu, MD; John R. Fowler, MD
University of Pittsburgh Medical Center, Pittsburgh, PA
Purpose The association of electrophysiological and sonographic findings with symptom severity and functional status in CTS has been poorly investigated. The purpose of this study was to identify whether electrodiagnostic testing or ultrasound demonstrated a stronger correlation with two-point discrimination and consequently constituted a better predictor of carpal tunnel severity.
Methods A retrospective review of 215 consecutive patients with carpal tunnel symptoms referred to an upper extremity practice was conducted in the current study. All patients were evaluated with static two-point discrimination (2-PD) of the thumb, index and middle finger of the affected hand. A 2-PD ?6 mm was considered a positive finding. All patients underwent ultrasound testing to calculate the median nerve cross-sectional area (CSA), as well as electrodiagnostic testing. A median cross-sectional area of ?10 mm2, a distal motor latency (DML) of ?4.2 ms and a distal sensory latency (DSL) of ?3.2 ms were considered to be positive findings. Correlations between 2-PD and either DML, DSL or median CSA were calculated. Sensitivities, specificities and predictive values of abnormal DML and DSL (either alone or combined), as well as median CSA were also measured, using abnormal 2-PD as the standard reference.
Results Analysis failed to prove a statistically significant correlation between 2-PD and median CSA (r=015, p=0.2). A weak correlation was detected between 2-PD and EDX parameters, slightly stronger for DML (r=.33, p<0.0001), as compared to DSL (r=.26, p=0.0002). When 2-PD was used as a reference standard, EDX parameters combined had the greatest sensitivity (85%), followed by ultrasound (79%). Ultrasound had a greater sensitivity than DML (74%) and DSL (74%), used alone. All parameters demonstrated a very low specificity.
Conclusions EDX is the only test to demonstate a weak correlation with abnormal 2-PD, and as such is a better even though weak predictor of disease severity. However, ultrasound remains a promising evolving field.
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