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Predictive value of serologic tests for syphilis in otology
Abstract:
Otologic syphilis (luetic inner ear disease) usually is diagnosed by positive serologic tests and by exclusion of other possible causes. Because the FTA-ABS for syphilis is exquisitely sensitive in all but early primary cases, a positive FTA-ABS result and coincident inner ear disease often are thought to be diagnostic of syphilitic inner ear disease. The result is a management dilemma: are there false-positive results in misdiagnosed cases? Over 4 years, the authors performed a prospective study with time-matched controls to determine the predictive value of serologic tests and prevalence of syphilis in otology. Thirty-one cases of otologic syphilis were diagnosed in 5,439 new (different) patients with otologic complaints. In the geographic area studied, this prevalence (570/100,000) was 25-fold greater than that of all reported cases of syphilis in the general population (22.7/100,000). The defined sensitivity of the FTA-ABS (100%) was nearly twofold greater than the measured sensitivity of the rapid plasma reagin (RPR, 55%) in otologic syphilis. Specificities were comparable; therefore, a positive FTA-ABS had higher predictive value than a positive RPR. The prevalence-related predictive value of a positive FTA-ABS (22%) was more than twice that of the RPR (9%) in otology. The predictive value of a positive FTA-ABS in otology was 11-fold greater than that of the FTA-ABS in the general population (2%). Therefore, in suspect cases the FTA-ABS should be used to screen for otologic syphilis in an otologic practice. At a prevalence of 570 cases in 100,000 patients, only 22% of otologic patients with positive FTA-ABS results actually have otologic syphilis. Because disease morbidity can be far worse than treatment morbidity, however, positive results should be considered true-positives to avoid misdiagnosis in potentially infected patients. In suspect cases with positive FTA-ABS, therefore, treatment should be recommended unless specific contraindications exist.