High resolution CT (HRCT) in miliary tuberculosis (MTB) of the lung: correlation with pulmonary function tests & gas exchange parameters in North Indian patients

Abstract

Background & Objective: High resolution computed tomography (HRCT) scans are known to be helpful in early diagnosis and management of patients with miliary tuberculosis (MTB). We made an attempt in this study to identify patterns of pulmonary MTB on HRCT and to correlate the HRCT disease extent with pulmonary function tests (PFT) and gas exchange analysis (GEA). Methods: A total of 16 non-HIV patients with MTB underwent HRCT of the chest, PFT and GEA. All the investigations in these patients were completed within 20 days of presentation. Evidence of TB was diagnosed by biopsy from lymph nodes (3/16), organ biopsy [skin, liver, bone marrow and lung (transbronchial) (6/16)]. In one patient fundoscopy revealed choroid tubercles. In 6 patients, diagnosis was confirmed by clinical/radiological improvement following anti-tuberculosis therapy. Radiological patterns of involvement on HRCT of the lungs were studied and disease extent was estimated in each case by consensus between two radiologists using specially devised visual scoring system. Disease extent was correlated with PFT and GEA. Spearman rank correlation was used for statistical analysis. Results: Findings on HRCT in MTB included miliary nodularity (16/16), alveolar lesions such as ground glass attenuation and/or consolidation (5/16), lymphadenopathy (8/16), peribronchovascular interstitial thickening (1/16), emphysema (1/16), pleural pathology (2/16), and pericardial effusion (2/16). A significant correlation was noted between disease extent score and forced vital capacity (FVC) (r = −0.76; P=0.003), forced expiratory volume in one second (FEV₁)(r = −0.74; P = 0.005), total lung capacity (TLC) (r = −0.66; P = 0.037), oxygen saturation in arterial blood (SaO₂) (r = −0.69, P = 0.01), diffusion capacity of the lung (DLco) (r = −0.8; P = 0.02). Interpretation & Conclusion: Our findings showed that HRCT reliably diagnosed MTB, and thus could help in predicting derangement of pulmonary function tests and GEA in these patients.