Improvement in Diagnosis of Histoplasma Meningitis by Combined Testing for Histoplasma Antigen and Immunoglobulin G and Immunoglobulin M Anti-Histoplasma Antibody in Cerebrospinal Fluid

Abstract

Background: Central nervous system (CNS) histoplasmosis is a life-threatening condition and represents a diagnostic and therapeutic challenge. Isolation of Histoplasma capsulatum from cerebrospinal fluid (CSF) or brain tissue is diagnostic; however, culture is insensitive and slow growth may result in significant treatment delay. We performed a retrospective multicenter study to evaluate the sensitivity and specificity of a new anti-Histoplasma antibody enzyme immunoassay (EIA) for the detection of IgG and IgM antibody in the CSF for diagnosis of CNS histoplasmosis, the primary objective of the study. The secondary objective was to determine the effect of improvements in the Histoplasma galactomannan antigen detection EIA on the diagnosis of Histoplasma meningitis.

Methods: Residual CSF specimens from patients with Histoplasma meningitis and controls were tested for Histoplasma antigen and anti-Histoplasma immunoglobulin G (IgG) and immunoglobulin M (IgM) antibody using assays developed at MiraVista Diagnostics.

Results: A total of 50 cases and 157 controls were evaluated. Fifty percent of patients with CNS histoplasmosis were immunocompromised, 14% had other medical conditions, and 36% were healthy. Histoplasma antigen was detected in CSF in 78% of cases and the specificity was 97%. Anti-Histoplasma IgG or IgM antibody was detected in 82% of cases and the specificity was 93%. The sensitivity of detection of antibody by currently available serologic testing including immunodiffusion and complement fixation was 51% and the specificity was 96%. Testing for both CSF antigen and antibody by EIA was the most sensitive approach, detecting 98% of cases.

Conclusions: Testing CSF for anti-Histoplasma IgG and IgM antibody complements antigen detection and improves the sensitivity for diagnosis of Histoplasma meningitis.

Keywords: antibody; antigen; diagnosis; histoplasmosis; meningitis.

Figure 1.

The study population and classification of cases and controls. Individual case specimens: patients with central nervous system (CNS) histoplasmosis accrued through clinical testing at MiraVista Diagnostics from outside institutions besides Indiana University Medical Center (IUMC), University of Kentucky Medical Center (UKMC), and Vanderbilt University Medical Center (VUMC). Clinical suspected specimens: unique patients with specimen submitted for testing at MiraVista Diagnostics from IUMC, UKMC, and VUMC based on clinical concern for CNS histoplasmosis. This group includes cases that met the criteria for diagnosis of meningitis (cases) and patients that did not meet those criteria (controls). Alternative diagnosis specimens: patients (controls) with no clinical suspicion for CNS histoplasmosis, in whom no specimens were submitted for testing at MiraVista Diagnostics but from whom cerebrospinal fluid specimens were obtained from the microbiology laboratories at IUMC.

Figure 2.

Histoplasma antigen and anti-Histoplasma antibody results in cerebrospinal fluid in the cases and controls. For antigen testing, results <0.3 ng/mL (indicated by the solid line shown at 0.3 ng/mL) were considered negative, whereas results of ≥0.3 ng/mL were positive, below the limit of quantification at 0.4 ng/mL. Antigen results >19 ng/mL were above the limit of quantification. Results indicated by the number at the bottom of each of the antigen columns represent negative results because the space below the line designating the cutoff for positivity would not permit depiction of individual results for the controls. For antibody testing, results <8 units (indicated by broken horizontal line) were negative, results between 8 and 9.9 units were indeterminate, and results of 10 units (indicated by solid horizontal line shown at 10 units) or higher were positive. Results indicated by the number at the bottom of each of the antibody columns represent negative results because the space below the line designating the cutoff for positivity would not permit depiction of individual results for the controls, and the 32 cases in the immunoglobulin M column. Abbreviations: IgG, immunoglobulin G, IgM, immunoglobulin M; n, number of patients with negative results .