Randomized prospective crossover study of interstim lead wire placement with curved versus straight stylet

To assess whether InterStim lead wire placement with the curved stylet achieves motor response at lower amplitudes compared to straight stylet use.

This was a prospective, randomized, crossover study of patients scheduled for InterStim lead wire placement. All patients underwent lead wire testing with both the curved and straight stylets. Patients were randomized to determine stylet order, and then crossed-over to the alternate. Intra-operatively, the amplitude achieving motor response at each electrode was recorded. The stylet with lowest overall amplitudes was used for final placement. Primary outcome measure was amplitude requirement in the two deepest (0 and 1) electrodes. Secondary outcomes included amplitudes at the number 2 and 3 electrodes, combined amplitudes, stylet order, and adverse outcomes.

Forty-two patients were enrolled, 40 of whom were included in the final analysis. Mean age was 69 years (SD = 12.8) and mean BMI 27 (SD = 5.6). Indications for placement included: urge urinary incontinence (N = 26), urge/frequency (N = 25), non-obstructive urinary retention (N = 5), and fecal incontinence (N = 10). There were no significant differences between randomized groups. Regardless of order, the curved stylet achieved a motor response at lower amplitudes in the deepest electrodes (P < 0.001). Combined amplitudes of all electrodes were also significantly lower with the curved stylet (P < 0.001). Subsequently, 88% underwent final "optimal" placement with curved stylet (N = 35).

The curved stylet for InterStim lead wire placement consistently achieved motor response at lower amplitudes. A brief intra-operative exchange of stylets represents a minor procedural alteration that could maximize Implantable Pulse Generator battery life and facilitate programming.