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Ultrasound used as first line examination in the surgeon’s office:
Diagnostic accuracy of Wrist-to-Forearm Ratio in Carpal Tunnel
Syndrome
Jeppe Lange
Orthopaedic Research Unit – Department of Orthopaedic surgery, Aarhus
University Hospital & Center f
Background:
Attention has recently been brought to the possibility of
utilizing ultrasound for diagnosing carpal tunnel syndrome
Purpose / Aim of Study:
This study evaluates the diagnostic accuracy of
ultrasound used in the surgeon’s office as a first-line exam in carpal tunnel
syndrome.The primary outcome parameter was to assess whether a wrist-
forearm ratio cut-off value of 1.5 is diagnostic of carpal tunnel syndrome.
Materials and Methods:
The study was performed as a prospective controlled
study in 16 carpal tunnel syndrome patients diagnosed with positive nerve
conduction study and 32 controls case- matched by gender, age and hand.
Ultrasound exam of the median nerve was performed at the level of the distal
flexor wrist crease (wrist level) and 10 cm proximal of the distal flexor wrist
crease (forearm level) with calculation of cross sectional area.
Findings / Results:
Statistically significant differences were found between
patients and controls by both the cross sectional area and wrist-forearm ratio.
Both showed high specificity and positive predictive values at optimal cut-off
values. Optimal cut-off values were identified by receiver operator
characteristic at a 14 mm2 cross sectional area and a 1.6 wrist-forearm ratio.
The accuracy of the wrist-forearm ratio using a cut-off value of 1.5 and disease
prevalence of 33% gave a sensitivity of 94% (95% CI: 70% -100%),
specificity of 63% (95% CI: 44% -79%), a NPV of 95% (95% CI: 76% -100%)
and a PPV of 56% (95% CI: 35% -75%).
Conclusions:
This study shows that ultrasound evaluation of the median nerve
is a valuable and easily applied tool as a first-line diagnostic test used by the
hand surgeon for examination of patients with presumed carpal tunnel
syndrome. Owing to the high positive predictive value of ultrasound, the need
for referral to nerve conduction study may be limited.
