Sensitivity and specificity of lumbar puncture in HIV-infected patients with syphilis and no neurologic symptoms.

Abstract

TO THE EDITOR—We read with interest the article by Ghanem et al. [1] that addressed the controversial issue of the role of lumbar puncture in human immunodeficiency virus (HIV)-infected patients with syphilis who had no neurologic symptoms. The study examined the sensitivity and specificity of the 2 following criteria for the performance of lumbar puncture for the detection of asymptomatic neurosyphilis in these patients: (1) presence of late latent syphilis or syphilis of unknown duration (currently recommended by the Centers for Diseases Control and Prevention) [2] and (2) a CD4 cell count ⩽350 cells/µL and a rapid plasma reagen titer ⩾1:32 [1]. In countries where HIV-infected patients are provided with easier access to HIV care and longitudinal, periodical follow-up for immunological and virological status ofHIV infection and occurrences of syphilis, the study by Ghanem et al. [1] indeed provides important data that should encourage more research on appropriate management of syphilis in HIV-infected patients. Although there is no doubt with respect to the sensitivity of their criteria, we believe that the calculation of the specificity of the criteria is incorrect. The specificity, which is defined as the number of true-negative results divided by the sum of true-negative and false-positive results, would be 23.7% (9 true-negative results divided by the sum of 9 true-negative results and 29 false-positive results) for the criterion of late latent syphilis or syphilis of unknown duration and 13.2% (5 true-negative results divided by the sum of 5 true-negative results and 33 false-positive results) for the criterion based on CD4 cell count and/or high rapid plasma reagin titer. The lower specificity may be related to nonspecific inflammatory reaction of the cerebrospinal fluid during the course of HIV infection. Despite a good sensitivity of a test, the positive predictive value would be low if the specificity is low in the context of a low prevalence of a certain disease. In this case, the positive predictive value would be <25% if the prevalence of asymptomatic neurosyphilis was 20%. In the study by Ghanem et al. [1], a high retreatment rate was noted among HIV-infected patients with syphilis after a median duration of follow-up of 4 years (36% among those who underwent lumbar puncture and 38% among those who did not undergo lumbar puncture). The possible explanation for the high retreatment rate might be high-risk behavior causing reinfection with syphilis in these patients; this explanation is consistent with the findings in a population-based study from Peru in which the reinfection rate was 42% and retreatment was needed [3]. In addition, an initial sexually transmitted disease is significantly associated with subsequent sexually transmitted diseases [4]. Although more longitudinal follow-up studies and intensive counseling to prevent reinfection are clearly needed, the need for lumbar puncture may be reduced for patients without neurologic symptoms who are at high risk for recurrent syphilis in a setting where access to routine follow-up for syphilis or other sexually transmitted diseases and retreatments are provided. Potential conflicts of interest. All authors: no conflicts.