Effect of lidocaine iontophoresis on pain during needle electromyography

Pain during needle electrode examination (NEE) is often poorly tolerated. No previous studies have evaluated the effect of lidocaine iontophoresis on pain reduction during NEE. Our objective was to determine whether pretreatment with lidocaine iontophoresis mitigates the pain felt during NEE.

In this prospective randomized, placebo-controlled, double-blinded study, the subjects were recruited from among patients scheduled for electromyographic evaluation of the bilateral upper limbs in a hospital-based clinic; they were randomized to receive either lidocaine (4%) or placebo (normal saline) administered through iontophoresis (40 mA/min) to the left opponens pollicis. The right opponens pollicis was untreated. A bilateral opponens pollicis NEE was then performed in standard fashion using a monopolar needle electrode, immediately after which the subjects rated their pain using a 10-cm Visual Analog Scale.

Fourteen subjects were studied. Paired t tests revealed that iontophoresis significantly decreased pain (untreated side: 6.61 ± 1.96, n = 7; treated side: 4.63 ± 2.90, n = 7; P < 0.05). However, there were no significant side-to-side differences in either group (lidocaine: 7.29 ± 1.56 vs. 5.63 ± 3.12; P = 0.19 and placebo: 5.93 ± 2.19 vs. 3.63 ± 2.48; P = 0.1).

Pretreatment with iontophoresis significantly reduced pain during NEE. However, the lack of group differences between lidocaine and saline iontophoresis suggested that the analgesic effect may have been attributable primarily to the iontophoresis modality itself rather than to the medication administered with iontophoresis.