ATS/JRS/ALAT Guidelines for Humidifier Lung and Summer-Type Hypersensitivity Pneumonitis

Abstract Background: The ATS/JRS/ALAT Guidelines for the Diagnosis of Hypersensitivity Pneumonitis (GL for HP) were published in 2020. Humidifier lung and summer-type HP are forms of HP, but it is unclear whether they can be diagnosed using the GL for HP. This study examined the level of confidence with which humidifier lung and summer-type HP can be diagnosed with the GL for HP.Methods: Data from 23 patients with humidifier lung and 20 patients with summer-type HP (mean age, 67.3 and 57.4 years, respectively) diagnosed between October 2012 and January 2022 were retrospectively reviewed. We evaluated high resolution computed tomography (HRCT) patterns, bronchoalveolar lavage fluid (BALF) findings, exposures, and histopathological findings to determine the level of confidence with which a diagnosis of HP could be made using the GL for HP. Results: HRCT pattern was classified as typical HP in 5 (22%) and compatible with HP in 18 (78%) patients with humidifier lung and judged as typical HP in 17 (85%) and compatible with HP in 3 (15%) summer-type-HP patients. The confidence level for diagnosis of HP was definite in 2 (8.7%), moderate in 14 (60.9%), and low in 7 (30.4%) patients with humidifier lung. It was definite in 12 (60%), high in 3 (15%), and moderate in 5 (25%) patients with summer-type HP.Conclusions: The GL for HP showed utility in the diagnosis of humidifier lung in many patients with a moderate to low confidence. There was, however, a definite to high confidence for patients with summer-type HP.