Comparison of RigiScan and formal nocturnal penile tumescence testing in the evaluation of erectile rigidity.

Evaluation of male erectile function ideally should include measurement of axial rigidity expressed as grams force required to produce penile buckling. An axial rigidity more than 550 gm. is generally considered adequate for vaginal penetration. Unfortunately, this test cannot be done frequently and may disrupt sleep. An alternative method of determining rigidity is to use the RigiScan,* which makes repetitive measurements of radial rigidity at the base and tip of the penis expressed as per cent of normal maximum. Previous studies have demonstrated a positive correlation between axial and radial rigidity measurements but they have not been compared in patients with a wide range of erectile function. We performed a prospective study in a consecutive series of patients presenting with impotence comparing axial rigidity measured with a tonometer and radial rigidity measured by RigiScan. Erectile rigidity also was evaluated by a trained, blinded observer. Overall, RigiScan base and tip radial rigidity correlated well with axial rigidity (p < 0.002) and observer ratings (p < 0.003); axial rigidity similarly correlated well with observer ratings (p < 0.0001). However, when RigiScan base and tip radial rigidity exceeded 60% of maximum, there was a poor correlation with axial rigidity and observer ratings (p > 0.1). In this range, the RigiScan failed to discriminate axial rigidities between 450 and 900 gm. buckling force; however, axial rigidity in this same range again correlated well with observer ratings (p < 0.0001). Since an axial rigidity of more than 550 gm. is considered adequate for vaginal penetration, the RigiScan may not be able to detect mild abnormalities in erectile function. Further study is in progress to evaluate the significance of these findings but presently a RigiScan measurement of radial rigidity in excess of 60% of maximum should be interpreted cautiously and not necessarily regarded as normal. In this range further measurements of axial rigidity or observer ratings of rigidity may be necessary to establish the diagnosis.