Comparison of the International Index of Erectile Function erectile domain scores and nocturnal penile tumescence and rigidity measurements: does one predict the other?

OBJECTIVE To describe the relationship between the International Index of Erectile Function (IIEF) erectile domain score, and nocturnal penile tumescence and rigidity values measured by RigiScan (Timm Medical Technologies, Eden Prairie, MN). PATIENTS AND METHODS In all, 73 men were evaluated with the IIEF and 2 nights of continuous penile monitoring with the RigiScan. Twenty-six men were evaluated before and after prostatectomy, for a total of 99 pairs of data points. We dichotomized the RigiScan results as 'adequate' (no erectile dysfunction, ED), or 'inadequate' (having ED), based on the 'best erectile event' over the 2 nights of monitoring. Two separate criteria for adequate erectile function were used, one of > 70% rigidity for >= 10 min, and the other > 600/6 rigidity for >= 10 min. The erectile domain score of the IIEF was calculated in the standard fashion. RESULTS Using both the 70% and the 60% rigidity criteria, there was a statistically significant association between the IIEF erectile domain scores and the RigiScan data (r= 0.27, P = 0.008 and r = 0.29, P = 0.003, respectively). However, the sensitivity of the IIEF to predict ED based on RigiScan results using the 70% rigidity criteria was 68.90/6, and the specificity was 57.1%. When the IIEF was used as a continuous predictor of RigiScan results, the area under the receiver-operating characteristic (ROC) curve was 0.66. Using the 60% criteria, the sensitivity was 55.8% and the specificity was 73.2%; the area under the ROC curve was 0.72. CONCLUSIONS IIEF erectile domain scores and nocturnal penile tumescence and rigidity measurements are weakly associated, and the clinical utility of one test to predict the other is limited. However, because of the differences in the measured outcomes (perception of erectile function vs physiological capacity), a weak association does not disqualify either test's individual utility.