Introduction: Hypersensitivity pneumonitis is a complex pulmonary syndrome mediated by the immune system and caused by inhalation of antigens to which the patient has been previously sensitized. From the clinical point of view hypersensitivity pneumonitis can be divided into acute/subacute, and chronic phenotypes. It is characterized by an insidious onset of cough, dyspnea, fatigue, and weight loss that develop over several weeks to a few months. Case report: A 52-year-old patient came in February 2017 with high temperature, chest tightness, dyspnea, persistent cough, hemoptysis and weight loss of more than 6 kilograms. Radiography and computerized tomography showed poorly defined small diffuse centrilobular bilateral nodules. Inspiratory crackles were detected by physical examination. Routine laboratory tests were regular. Bronchoalveolar lavage fluid analysis and lung biopsies by video-assisted thoracoscopic surgery indicated the presence of diffuse lymphocytic infiltrates and giant cells with non-necrotizing granulomas and cellular bronchiolitis. Hypersensitivity pneumonitis diagnosed. She was given 35 mg deflazacort, bronchodilators to widen the airways and etamsilat pills. We did not identify the causative agents, including home, workplace and recreational environmental factors.Conclusion: Making the correct diagnosis has critical therapeutic and prognostic implications. Patients with hypersensitivity pneumonitis should be referred to expert centers, as the overlap with other forms of interstitial lung disease may be deceiving. The mainstay in managing this illness is to avoid the causative antigen, though complete removal is not always possible.

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