Early Diagnosis of Carpal Tunnel Syndrome: Comparison of Digit 1 with Wrist and Distoproximal Ratio
Abstract
Our objective in this study was to compare
the sensitivity and specificity of the
median sensory nerve conduction velocity
(SNCV) from digit 1 to wrist with those of
the distoproximal (D/P) ratio of the median
SNCV from palm to digit 3/palm to
wrist in the diagnosis of mild carpal tunnel
syndrome (CTS) by using a receiver
operating characteristic (ROC) curve. To
achieve this objective, we studied prospectively
(January 1997–October 1998)
370 patients referred for CTS. One hundred
forty-two patients (38.4%) with
moderate to severe CTS and 15 patients
(4.1%) with multiple (≥3) compressive
neuropathies in upper limbs with subclinical
peripheral neuropathy were excluded.
The remaining 213 patients (302
hands with mild CTS; 167 women; mean
age, 50 y ± 12 y) and 38 controls (71
hands; 25 women; mean age, 47 y ± 13 y)
had median and ulnar nerve conduction
studies. ROC curves were constructed for
median SNCV digit 1 to wrist and median
SNCV D/P ratio from the patients’ and
controls’ data. The median SNCV at ≤45.9
m/s, corresponding to an optimal cutoff
point on ROC curve, discriminated 89.5%
of mild CTS from controls with specificity
of 98.6%. The median D/P ratio at ≥1.12,
corresponding to an optimal cutoff point
© 2001 American Academy of Clinical
Neurophysiology
on ROC curve, discriminated 67.2% of mild CTS from controls with specificity of 97.2%.
Of the 10.3% (31/302) of hands in which digit 1 to wrist was within normal limits at the
selected optimal cutoff value (≤45.9 ms), 7% (21/302) had an abnormal D/P ratio
(≥1.12), and 3.3% (10/302) had a normal electrophysiologic examination. The likelihood
ratio (true-positive ratio to false-positive ratio, assessing the discriminative
power of a test) of the median SNCV digit 1 to wrist, at an optimal point on ROC curve
(63.9), was higher than that of the median SNCV D/P ratio (23.9, χ2 = 36.9, P < .001).
These findings suggest that the median SNCV digit 1 to wrist is more sensitive than the
median SNCV D/P ratio in the diagnosis of mild CTS.
the sensitivity and specificity of the
median sensory nerve conduction velocity
(SNCV) from digit 1 to wrist with those of
the distoproximal (D/P) ratio of the median
SNCV from palm to digit 3/palm to
wrist in the diagnosis of mild carpal tunnel
syndrome (CTS) by using a receiver
operating characteristic (ROC) curve. To
achieve this objective, we studied prospectively
(January 1997–October 1998)
370 patients referred for CTS. One hundred
forty-two patients (38.4%) with
moderate to severe CTS and 15 patients
(4.1%) with multiple (≥3) compressive
neuropathies in upper limbs with subclinical
peripheral neuropathy were excluded.
The remaining 213 patients (302
hands with mild CTS; 167 women; mean
age, 50 y ± 12 y) and 38 controls (71
hands; 25 women; mean age, 47 y ± 13 y)
had median and ulnar nerve conduction
studies. ROC curves were constructed for
median SNCV digit 1 to wrist and median
SNCV D/P ratio from the patients’ and
controls’ data. The median SNCV at ≤45.9
m/s, corresponding to an optimal cutoff
point on ROC curve, discriminated 89.5%
of mild CTS from controls with specificity
of 98.6%. The median D/P ratio at ≥1.12,
corresponding to an optimal cutoff point
© 2001 American Academy of Clinical
Neurophysiology
on ROC curve, discriminated 67.2% of mild CTS from controls with specificity of 97.2%.
Of the 10.3% (31/302) of hands in which digit 1 to wrist was within normal limits at the
selected optimal cutoff value (≤45.9 ms), 7% (21/302) had an abnormal D/P ratio
(≥1.12), and 3.3% (10/302) had a normal electrophysiologic examination. The likelihood
ratio (true-positive ratio to false-positive ratio, assessing the discriminative
power of a test) of the median SNCV digit 1 to wrist, at an optimal point on ROC curve
(63.9), was higher than that of the median SNCV D/P ratio (23.9, χ2 = 36.9, P < .001).
These findings suggest that the median SNCV digit 1 to wrist is more sensitive than the
median SNCV D/P ratio in the diagnosis of mild CTS.
Keywords
carpal tunnel syndrome, early diagnosis, median sensory nerve conduction velocity, digit one, distoproximal ratio, receiver operating characteristic curve, sensitivity, and specificity
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