Nerve conduction studies and EMG in carpal tunnel syndrome: Do they add value?

Abstract

This paper summarises the views of four experts on the place of neurophysiological testing (EDX) in patients presenting with possible carpal tunnel syndrome, in guiding their treatment, and in reevaluations. This is not meant to be a position paper or a literature review, and heterogeneous viewpoints are presented. Nerve conduction studies should be performed in patients presenting with possible carpal tunnel syndrome to assist diagnosis, and may need to be repeated at intervals in those managed conservatively. There is evidence that local corticosteroid injection is safe and effective for many patients, thereby avoiding or deferring surgical decompression. All patients should undergo EDX studies before any invasive procedure for CTS (injection or surgery). Needle EMG studies are not obligatory, but may be needed in those with severe disease and those in whom an alternate or concomitant diagnosis is suspected.

Keywords: Carpal tunnel syndrome; Conservative management; Local injection of corticosteroids; Median neuropathy at the wrist; Needle EMG; Nerve conduction studies; Surgical decompression.

Fig. 1

Calculated pre-test and post-test probability using two studies (Jackson et al., 1989; Stevens, 1987) adopted by Graham (2008) as stringent and lax criteria. Using the lax criterion, a patient with the pre-test probability of 0.85 will keep the post-test probability of 0.93 if NCS is abnormal, but the post-test probability will decline to 0.42 if NCS is normal. The results exactly agree with Fig. 1 in Graham (2008) using the stringent criterion.

Fig. 2

The probability of CTS estimated from symptoms vs neurophysiological severity of CTS in 2,695 subjects with hand symptoms. The probability of CTS (vertical axis) is derived from the algorithms used on www.carpal-tunnel.net. The higher the score, the more typical of CTS is the patient’s presentation. (As the degree of NCS abnormality increases it becomes more likely that a clinician will recognize the problem as CTS.) The neurophysiological severity was assessed as in Bland (2000a).

Fig. 3

Relationship between neurophysiological severity of CTS, assessed as in Bland (2000a), and subjective severity of symptoms in 29,594 tests in patients referred with possible CTS (some patients tested on more than one occasion). SSS = Boston/Levine symptom severity score for right hand at the time of test.

Fig. 4

Relationship between pre-operative neurophysiological grade, assessed as in Bland (2000a), and surgical outcome. Overall subjective opinion of the effect on symptoms of surgery for 7,410 routine NHS carpal tunnel decompressions. Patient opinions were collected 3 months to 2 years after surgery. Number of cases in each group is indicated in the bars.

Fig. 5

Popular grading schemes for CTS. For details of the grading criteria based on NCS, see (Padua et al., 1997, Stevens, 1997, Bland, 2000a).

Fig. 6

Change in neurophysiological grade from before to after surgery in 559 operations vs outcome of surgery. The neurophysiological severity was assessed as in Bland (2000a). Green bars show the percentage of patients with a given improvement in NCS results reporting that symptoms are completely cured or much improved. Red bars show the percentage of patients with a given change in NCS who report themselves worse after surgery.