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Early neurophysiological diagnosis of true neurogenic « thoracic outlet syndrome » (TOS)

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Early neurophysiological diagnosis of true neurogenic "thoracic outlet

syndrome" (TOS)

M.T. Hua, A. Dubuisson, B. Zeevaert, F.C. Wang (Liège, B)

UNLIKELY TOS Age Sex MACN (µV) Radial/MACN F Uln - F Med (ms) X-ray

1 54 M 11.0 1.5 -0.4 normal 2 56 W 9.6 3.1 2.0 normal 3 36 W 16.0 3.7 0.3 4 51 M 0.9 - 0.8 normal 5 44 W 10.0 1.8 2.0 normal 6 53 M 12.0 2.4 -0.7 normal 7 47 W 9.1 4.8 0.2 normal

VASCULAR TOS Age Sex MACN (µV) Radial/MACN F Uln - F Med (ms) X-ray

1 38 W 4.1 6.8 0.0 sp 2 44 W 15.0 2.7 0.0 normal 3 52 W 11.0 3.0 0.5 normal 4 39 M 8.4 2.6 1.4 normal 5 35 W 8.7 6.1 0.0 normal 6 48 W 6.2 3.5 -0.5 normal 7 45 W 9.1 3.5 1.8 + 8 33 W 12.0 3.4 0.4 normal 9 26 M 12.0 2.8 0.7 + 10 56 W 5 2.2 0.5 +

NEUROLOGIC TOS Age Sex MACN (µV) Radial/MACN F Uln - F Med (ms) X-ray

1 64 W 0.0 - -5.5 + 2 47 W 19.0 3.0 -0.6 normal 3 26 W 7.7 4.3 0.3 normal 4 63 W 8.1 5.9 0.0 normal 5 53 W 10.0 2.4 1.0 normal 6 27 W 9.3 4.0 -1.2 + 7 18 W 10.0 5.1 -0.5 normal 8 55 W 0.8 26.3 -6.6 + 9 53 W 4.5 4.0 -0.3 + 10 42 W 15.0 2.5 -0.2 normal

X-ray + MACN Radial/MACN F Uln - F Med

(µV) amplitude ratio (ms)

Healthy subjects Mean 18 2 1.1

(n = 52, M/W = 30/22) SD 5 1 0.8

(mean age = 29.0) Limit of normal >/= 7.7 </= 3.8 >/= -0.4

UNLIKELY TOS 0/6 Mean 9.8 2.5 0.6

(n = 7, M/W = 5/3) SD 4.6 1.6 1.1

(mean age = 48.6) Number of pathologic cases 1 1 1

VASCULAR TOS 3/10 Mean 9.6 3.7 0.5

(n = 10, M/W = 8/2) SD 3.1 1.5 0.7

(mean age = 41.6) Number of pathologic cases 2 2 1

NEUROLOGIC TOS 4/10 Mean 8.4 6.4 -1.4

(n = 10, M/W = 10/0) SD 5.8 7.5 2.6

(mean age = 44.8) Number of pathologic cases 3 7 5

B

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C

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O

N

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Patients and methods

Twenty-seven patients, diagnosed as having a TOS, were studied. The diagnosis was previously made by clinicians unrelated to our electrophysiological laboratory.

Each patient was called back. History taking, physical examination and neurography evaluation were systematically performed. All had a cervical spine radiograph and a vascular-doppler flow study, otherwise the request was made. No other entrapment neuropathy was diagnosed in these 27 patients.

According to their history, clinical features and vascular-doppler (Table 1), 3 groups were established : UNLIKELY TOS (n = 7, 4 women and 3 men, mean age = 48.7), VASCULAR TOS (n = 10, 8 women and 2 men, mean age = 41.6) and NEUROGENIC TOS with or without a vascular component (n = 10, 10 women, mean age = 44.8).

We studied the medial antebrachial cutaneous nerve amplitude (MACN SNAP amplitude), radial SNAP amplitude/MACN SNAP amplitude ratio and the difference between minimal F-M latenties of median and ulnar nerves (F ulnar - F median) in these 3 groups (in bilateral TOS, only the worst side was considered) and in a group of 52 healthy subjects.

Results

Control subjects: mean MACN amplitude was 18 ± 5 µV, lower limit of normal (LN) was 7.7 µV ; mean amplitude ratio was 2 ± 1 , upper LN was 3.8 ; mean F ulnar – F median was 1.1 ± 0.8 ms, lower LN was -0.4 ms (Table 3).

Pathologic features were distributed as follows : 1) C7 transverse process hypertrophy or cervical rib : 0/7 case in UNLIKELY TOS, 2/10 cases in VASCULAR TOS and 4/10 cases in NEUROGENIC TOS ; 2) MACN amplitude < 7.7 µV : 1/7 case in UNLIKELY TOS, 2/10 cases in VASCULAR TOS and 3/10 cases in

NEUROGENIC TOS ; 3) amplitude ratio

> 3.8 : 1/7 case in UNLIKELY TOS, 2/10 cases in VASCULAR TOS and 7/10 cases in NEUROGENIC TOS ; 4) F ulnar – F median < -0.4 ms : 1/7 case in UNLIKELY TOS, 1/10 cases in VASCULAR TOS and 5/10 cases in NEUROGENIC TOS (Tables 2 and 3).

Conclusion

Our results suggest that the amplitude ratio (radial SNAP amplitude/MACN SNAP amplitude) is more sensitive than the MACN amplitude for the diagnosis of TOS. The difference between F-wave latenties of median and ulnar nerves (F median 0.4 ms longer than F ulnar) can strengthen the presumption of TOS, as far as there is no associated carpal tunnel syndrome.

UNLIKELY TOS VASCULAR TOS NEUROLOGIC TOS

paresthesia : medial side of the upper limb - + +

weakness : hand intrinsic muscles - - /+ +

sensory loss : medial side of forearm and/or hand - - +

strength decrease : thenar > hypothenar - - +

VASCULAR-DOPPLER - + - /+

•X-ray + = C7 transverse process hypertrophy or cervical rib •MACN : medial antebrachial cutaneous nerve

•Uln : ulnar ; Med : median ; M : man ; W : woman

Table 1 Table 2

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