COMPARISON OF RIGISCAN AND FORMAL NOCTURNAL PENILE TUMESCENCE TESTINGIN THE EVALUATION OF ERECTILE RIGIDITY

Evaluation of male erectile function ideally should include measuremen t of axial rigidity expressed as grams force required to produce penil e buckling. An axial rigidity more than 550 gm. is generally considere d adequate for vaginal penetration. Unfortunately, this test cannot be done frequently and may disrupt sleep. An alternative method of deter mining rigidity is to use the RigiScan, which makes repetitive measur ements of radial rigidity at the base and tip of the penis expressed a s per cent of normal maximum. Previous studies have demonstrated a pos itive correlation between axial and radial rigidity measurements but t hey have not been compared in patients with a wide range of erectile f unction. We performed a prospective study in a consecutive series of p atients presenting with impotence comparing axial rigidity measured wi th a tonometer and radial rigidity measured by RigiScan. Erectile rigi dity also was evaluated by a trained, blinded observer. Overall, RigiS can 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 Rigi Scan 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 be tween 450 and 900 gm. buckling force; however, axial rigidity in this same range again correlated well with observer ratings (p < 0.0001). S ince an axial rigidity of more than 550 gm. is considered adequate for vaginal penetration, the RigiScan may not be able to detect mild abno rmalities in erectile function. Further study is in progress to evalua te the significance of these findings but presently a RigiScan measure ment of radial rigidity in excess of 60% of maximum should be interpre ted cautiously and not necessarily regarded as normal. In this range f urther measurements of axial rigidity or observer ratings of rigidity may be necessary to establish the diagnosis.