Hypersensitivity pneumonitis: the importance of the radiologist in the multidisciplinary approach to its diagnosis

Radiol Bras. 2016 Mar/Abr;49(2):VII–VIII Hypersensitivity pneumonitis encompasses a set of diseases with pulmonary involvement and a predominance of histopathologic findings—lymphocytic inflammatory infiltrate, noncaseating granulomas, and foci of bronchiolitis obliterans, as well as fibrosis in the more chronic stages—predominantly distributed around the small airways, as shown in the excellent correlation study conducted by Torres et al., published in this issue of Radiologia Brasileira. That distribution of findings reflects a response to repeated inhalation of various antigenic substances, typically organic substances, such as fungi, thermophilic bacteria, and bird feathers. Farmer’s lung and bird fancier’s lung are well-established forms of hypersensitivity pneumonitis. However, new and curious forms are described every day, such as “saxophonist’s lung”, which is caused by exposure to molds that grow in the mouthpieces of saxophones. Clinically, hypersensitivity pneumonitis can present in acute, subacute, or chronic forms. The acute and subacute forms have systemic symptoms, mimicking those of flu or asthma. The chronic form occurs in individuals with greater re-exposure to antigens, evolving to more pronounced interstitial fibrosis, dyspnea, hypoxemia, digital clubbing, and impaired lung function. The chronic form is also usually associated with failure to identify the causative antigen, and the differential diagnosis includes other idiopathic interstitial lung diseases, although making that distinction is often impossible even with the histopathological findings. There is considerable variation across epidemiological studies of hypersensitivity pneumonitis. It is estimated that hypersensitivity pneumonitis accounts for 3–13% of all cases of interstitial lung disease in Brazil. A study conducted in the city of São Paulo, SP, Brazil, involving 99 cases of lung biopsy-confirmed hypersensitivity pneumonitis, indicated that the most frequent causative agents are household mold and bird droppings. In our experience in the Brazilian state of Santa Catarina, we have also found that the disease occurs most frequently in individuals exposed to mold in the home and in individuals who are bird breeders.