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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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