Role of interferon gamma release assay in the diagnosis of Pott disease.

Abstract

Tuberculosis is ubiquitous in its presence and in its myriad manifestations. Despite several advances, it often poses a diagnostic dilemma. The aim of this study was to evaluate the efficacy of the QuantiFERON assay in the diagnosis of Pott disease. In this study, 70 consecutive patients with vertebral collapse underwent a battery of investigations including radiological evaluation (MR imaging and chest and spine radiography), routine blood workup (hemoglobin, total leukocyte count, differential leukocyte count, and erythrocyte sedimentation rate), enzyme-linked immunosorbent assay (ELISA) for tuberculosis, a bone scan and the QuantiFERON assay, perioperative evaluation, and bacteriological studies. The patients were then classified as having tuberculosis on the basis of positive smear or culture, a biopsy consistent with tuberculosis, or a therapeutic response to antituberculosis chemotherapy on follow-up. The efficacy of the investigations, both individually and in combination, were evaluated. Tuberculosis was diagnosed in 51 patients, and 19 had vertebral collapse that was attributable to other causes. Based on the authors' data, sensitivity of the QuantiFERON assay in the diagnosis of tuberculosis of the spine was 84% and specificity was 95%. In combination with radiological criteria, bone scan, and ELISA, the QuantiFERON assay was predictive of tuberculosis in 90% of cases (46 patients). None of the investigative modalities individually are efficacious enough to make a diagnosis of tuberculosis of the spine with such a degree of certainty as to to obviate the need for a tissue diagnosis or bacteriological confirmation. The ELISA, MR imaging of the spine, and bone scanning findings provide a reasonably certain diagnosis in 90% of cases, providing the grounds for starting a safe trial of antituberculous chemotherapy.