ObjectiveTo strengthen the understanding to hypersensitivity pneumonitis and make early diagnosis and standard treatment by analyzing the clinical features, the diagnosis and treatment of a patient diagnosed as hypersensitivity pneumonitis presenting as progressive fibrotic interstitial lung disease in combination with literature review.MethodsThe diagnosis and treatment process and relevant clinical data of the patient were analyzed retrospectively and literatures were reviewed. Based on 282 relevant literatures, the diagnostic methods, treatment and prognostic factors of hypersensitivity pneumonitis were summarized.ResultsThe patient, female, 45 years old, self-employed, was admitted to the hospital due to "cough, sputum for 9 years, dyspnea for more than 6 months" without obvious extrapulmonary clinical manifestations. Creaks at the bottom of the lungs and clubbed toes were found through physical examination. High-resolution computed tomography indicated that the main manifestations were ground glass and grid-like shadows, presenting characteristics of interstitial pneumonia. The pulmonary lesions aggravated gradually, and part of the lung lobe presented honeycomb lung at the time of diagnosis. Eight years ago, she performed fibrobronchoscopy in other hospital revealing an increased lymphocyte proportion (39%) in bronchoalveolar lavage fluid. Lung function suggested very severe restrictive ventilation dysfunction. She was given prednisone for a short time, and the drug was stopped by herself with uncertain efficacy. Later, she performed frozen lung biopsy suggesting peribronchiolar metaplasia interstitial broadening with lymphocytic infiltration, without granuloma or fibroblast lesions. No obvious abnormity was seen in makers of infections and immunology. At this point, the patient was clearly diagnosed as hypersensitivity pneumonitis. Meanwhile, the patient's pulmonary lesions were still mainly made of ground glass and plaques, partly with changes like honeycomb. Poor response was obtained with anti-inflammatory treatment of prednisone for 3 months and anti-fibrosis treatment of pirfenidon for more than 2 months. Literature review resulted in 87 patients, including 39 males (44.82%) and 48 females (55.18%), with an average age of (47.0±18.4) years. Seventy patients (80.46%) had clear allergens. 3.45% patients' lymphocyte percentage in bronchoalveolar lavage fluid ranged from 20% to 39%, and 19.54% patients' lymphocyte percentage was more than 40%. 4.60% of the patients achieved remission through detachment from allergens; 71.27% of the patients achieved remission with glucocorticoid treatment, 14.94% improved with glucocorticoid treatment, and 1.15% died; 6.89% of the patients achieved remission after receiving anti-allergy therapy. Patients with chronic hypersensitivity pneumonia were found with poor prognosis.ConclusionsIn patients with diffuse interstitial pulmonary fibrosis with unknown cause, transbronchoscope freezing lung biopsy as early as possible is a feasible method for early diagnosis and improving prognosis. Patients with hypersensitivity pneumonitis with a long course of pulmonary fibrosis have a poor response to glucocorticoid and other classic treatments, and most of them have a poor prognosis.