Novel diagnostic approach to carpal tunnel syndrome Wang FC, Gérard P, Iserentant C CHU Liège RBSPRM Annual Congress, december 2, 2005

Background The Carpal Tunnel Syndrome (CTS), a condition in which the median nerve is compressed within the carpal tunnel where it passed under the trans-carpal ligament (flexor retinculum), is the most frequent mononeuropathy in the world, with a prevalence in the adult population estimated at 3%. RBSPRM Annual Congress, december 2, 2005

Objectives To answer this question : in patients clinically suspected of having CTS, what are the best electrodiagnostic (EDX) studies (with the highest sensitivity and specificity) to confirm the diagnosis ? RBSPRM Annual Congress, december 2, 2005

AAEM Quality Assurance Committe criteria Prospective study design Diagnosis of CTS in patient population based on clinical criteria independent of the EDX procedure under evaluation EDX procedure described in sufficient detail to permit replication Limb temperature monitored (> 32°C) Reference values for EDX obtained with concomitant study of a reference population Criteria for abnormal findings clearly stated and defined in statistically computed terms RBSPRM Annual Congress, december 2, 2005

Methods Conduction slowing through the carpal tunnel was evaluated in 3 ways: Absolute slowing : prolonged distal motor latency and reduced sensory conduction velocity of the median nerve through the carpal tunnel Relative slowing : difference between median and ulnar nerves Relative slowing : difference between two distinct nerve segments of the median nerve RBSPRM Annual Congress, december 2, 2005

Median palm-wrist mixed orthodromic conduction (med SCV) G1 : 3 cm bar electrode, at the proximal wrist crease, between the tendons of the flexor carpi radialis and palmaris longus G2 : proximal to G1 Cathode : 8 cm distal to G1, in the mid-palm Anode : distal to the cathode RBSPRM Annual Congress, december 2, 2005

Difference in velocity between the mixed orthodromic conductions of the ulnar and median nerves in the palm-wrist segment (med-uln SCV) RBSPRM Annual Congress, december 2, 2005

Orthodromic 14-7 distoproximal ratio (14-7 method or Twin Peak test) G2 : at the proximal wrist crease, between the tendons of the flexor carpi radialis and palmaris longus G1 : mid-palm, 7 cm distal to G2 Cathode : 7 cm distal to G1, (third digit) Anode : distal to the cathode RBSPRM Annual Congress, december 2, 2005

Orthodromic 14-7 distoproximal ratio (14-7 method or Twin Peak test) Peak II/Peak I 3.2 ms/1.52 ms = 2.11 G1/G2 G2/G1 RBSPRM Annual Congress, december 2, 2005

Median distal motor latency (med DML) G1 (APB muscle) : halfway between the midpoint of the distal wrist crease and the first metacarpophalangeal joint (MPJ) G2 : slightly distal to the MPJ Cathode : 8 cm proximal to G1, in a line measured first to the midpoint of the distal wrist crease and then to a point slightly ulnar to the tendon of the flexor carpi radialis Anode : proximal to the cathode RBSPRM Annual Congress, december 2, 2005

Difference in distal motor latency between ulnar and median nerves with thenar recordings (uln-med DML) G1 and G2 : as for medDML Cathode : over the median nerve, than over the ulnar nerve at the wrist on the same line Anode : proximal to the cathode RBSPRM Annual Congress, december 2, 2005

Difference in distal motor latency between ulnar and median nerves with thenar recordings (uln-med DML) RBSPRM Annual Congress, december 2, 2005

Groups 22 dominant and 22 non dominant hands from healthy volunteers (45 ± 11 y.o. ; 170 ± 7 cm ; female : 59%) 29 dominant and 24 non dominant hands from patients with paresthesia in the territory of the median nerve worsening at night or upon awakening (at least at the onset) (53 ± 16 y.o. ; 163 ± 8 cm ; female : 75%) 20 dominant and 20 non dominant hands from patients without paresthesia (39 ± 14 y.o. ; 167 ± 6 cm : female : 70%) RBSPRM Annual Congress, december 2, 2005

Reference values (from healthy volunteers) Mean SD Mean ±1.65SD Mean ±1.96SD Mean ±2.30SD med SCV domi non domi 59 5.5 5.6 50 49 48 47 uln-med SCV 3.4 3.9 6.3 4.7 14 12 16 13 18 15 14-7 method 1.9 0.11 0.10 2.09 2.13 2.12 2.16 2.15 med MDL 3.3 0.32 0.26 3.8 3.7 4.0 med-uln MDL 0.5 0.21 0.9 0.8 1.0 1.1 Normal distribution Unilateral tests Mean ± 1.65SD :  = 0.05 Mean ± 1.96SD :  = 0.025 Mean ± 2.30SD :  = 0.01 med MDL RBSPRM Annual Congress, december 2, 2005

Sensitivity and specificity (established by confronting patients, with and without paresthesia, to the reference values) Specificity fixed at 97% Mean ±1.65SD Mean ±1.96SD Mean ±2.30SD med SCV sensitivity specificity 77% 87% 90% 85% 92% 83% uln-med SCV 91% 88% 100% 81% 14-7 method 70% 73% 95% 97% med MDL 57% 75% 64% med-uln MDL 79% 72% 66% Relative methods are more sensitive and specific than absolute measurements Motor axons are less vulnerable to compression than sensory axons RBSPRM Annual Congress, december 2, 2005

ROC curves Sensitivity RBSPRM Annual Congress, december 2, 2005 med MDL med-uln MDL med SCV uln-med SCV 14-7 method Relative methods are more sensitive and specific than absolute measurements Motor axons are less vulnerable to compression than sensory axons Sensitivity

Novel Diagnostic Approach : 100% of specificity 89% of sensitivity med SCV and uln-med SCV (LN : 50 m/s and 14 ms) Both abnormal One normal, one abnormal Both normal 14-7 method (LN : 2.09) Abnormal Normal med DML and med-uln DML (LN : 3.8 ms and 0.9 ms) Sensory CTS Sensory motor CTS No CTS