CAN CT DISTINGUISH HYPERSENSITIVITY PNEUMONITIS FROM IDIOPATHIC PULMONARY FIBROSIS

OBJECTIVE. The clinical management of patients with idiopathic pulmona ry fibrosis differs markedly from that of patients with hypersensitivi ty pneumonitis. However, the two diseases often cannot be differentiat ed on clinical grounds. The purpose of this study was to establish whe ther CT can be used to make the distinction. MATERIALS AND METHODS. Th irty-six patients with idiopathic pulmonary fibrosis and 27 patients w ith hypersensitivity pneumonitis were studied. All diagnoses were conf irmed or supported by open lung biopsy. Three of the patients with idi opathic pulmonary fibrosis had desquamative interstitial pneumonia, an d the remainder had usual interstitial pneumonia. In 19 of the 27 pati ents with hypersensitivity pneumonitis, the disease was chronic (sympt oms lasting more than 1 year), while eight had acute or subacute sympt oms. Two radiologists, who had not previously seen any of the cases an d were blinded to the diagnosis, reviewed the CT images by consensus. The extent and distribution of CT features (including ground-glass att enuation, honeycombing, and micronodules) were recorded. In each case, a CT diagnosis was made, and the level of diagnostic confidence was r ecorded. RESULTS. A CT diagnosis was made with a high level of confide nce in 39 (62%) of 63 patients. In these patients, the CT diagnosis wa s correct in 35 cases (90%): 23 of 26 patients with a CT diagnosis of idiopathic pulmonary fibrosis and 12 of 13 patients with a CT diagnosi s of hypersensitivity pneumonitis, In the three patients with desquama tive interstitial pneumonia, the CT diagnoses were probable hypersensi tivity pneumonitis in two cases and definite hypersensitivity pneumoni tis in one case. Of the 19 patients with chronic hypersensitivity pneu monitis, only seven had a definite diagnosis of hypersensitivity pneum onitis based on CT findings; three had a definite diagnosis of idiopat hic pulmonary fibrosis. The patients with idiopathic pulmonary fibrosi s and usual interstitial pneumonia were more likely to have honeycombi ng and peripheral or lower lung zone predominance of disease, and less likely to have micronodules, than were patients with chronic hypersen sitivity pneumonitis, The patients with idiopathic pulmonary fibrosis and desquamative interstitial pneumonia had widespread ground-glass op acity indistinguishable from some cases of acute or subacute hypersens itivity pneumonitis. CONCLUSION. Our results show that CT can be used to distinguish idiopathic pulmonary fibrosis from hypersensitivity pne umonitis in most but not all cases. Desquamative interstitial pneumoni a cannot reliably be distinguished from acute or subacute hypersensiti vity pneumonitis. Chronic hypersensitivity pneumonitis may have findin gs identical to those of usual interstitial pneumonia. Lung biopsy sho uld still be considered the gold standard for diagnosis of interstitia l lung disease.