Introduction:
Diagnosis is based on combination of symptoms and electrophysiologic tests
Anatomy:
Anatomical space bounded anteriorly by flexor retinaculum and posteriorly by 8 carpal bones
Contents: median nerve and flexor tendons
(Median nerve has sensory supply to radial 3 1/2 fingers and motor supply to short abductor and opposing muscles of thumb, radial half of short flexors of thumb, and two lateral lumbricals)
Clinical features:
Sensory: Tingling and numbness of lateral 3 1/2 digits, nocturnal pain
Motor: Weakness of thumb, thenar atrophy
Autonomic: anhidrosis due to compression of median nerve
Phalen maneuver: tingling of fingers upon flexing the wrist for 60 seconds.
Tinel sign: tingling of fingers upon tapping median nerve at wrist
Causes:
Most are idiopathic
Others: Repetitive stress injury, RA, acromegaly, myxedema, pregnancy, oral contraceptives, acute or chronic trauma, amyloidosis
Rare: sarcoidosis, tuberculosis, Paget disease, vascular shunts
Extremely rare: anomalous superficial flexor muscle of fingers, anomalous lumbrical muscles, thrombosis of persistent median artery, bleeding dyscrasia, fibroma of tendon sheath, ganglion cyst, lipoma, lipofibromatous hamartoma of median nerve, osteochondroma leading to carpal tunnel syndrome
Electrophysiology:
Difference of more than 0.4 ms between the median and ulnar sensory peak latencies or a prolonged median distal motor latency of more than 4 msec
Ultrasound:
13MHz linear probe
Arms extended, forearms were supinated, wrists rested on flat surface, fingers semiextended
Transverse images of median nerve immediately proximal to the carpal tunnel inlet, at carpal tunnel inlet and at carpal tunnel outlet
Flexor retinaculum, seen as arched echogenic band, is used as landmark for the carpal tunnel, not bones and is seen anterior to the median nerve
Median nerve is seen superficial to the flexor tendons, seen as oval shaped well defined ehogenic structure with speckeled appearance proximal to the carpal tunnel and loses speckeled appearance distally and becomes less well defined
Cutoff of 0.09 - 0.11 sq.cm may be taken as cut-off
MRI:
Thickening of the median nerve
Flattening of the median nerve
Palmar bowing of the flexor retinaculum
References:
Wong SM et al. Carpal Tunnel Syndrome: Diagnostic Usefulness of Sonography. Radiology 2004;232:93-99
K Monagle K et al. Quantitative MR imaging of carpal tunnel syndrome. AJR Jun 1999; 172: 1581 - 1586.
Mallouhi A et al. Predictors of Carpal Tunnel Syndrome: Accuracy of Gray-Scale and Color Doppler Sonography. AJR May 2006; 186: 1240 - 1245
