patients with chronic hypersensitivity pneumonitis ( hp ) can present with an insidious onset of their disease without typical fluctuating flu - like symptoms , and there are only signs of chronic respiratory failure caused by the progressive fibrotic lung disease . a 45-year - old man with a pneumomediastinum and interstitial lung disease was referred for further investigations and therapy . the patient had been working in farming for almost 20 years and was exposed in childhood by his father to pigeon breeding from childhood until 20 years ago . high - resolution ct of the lung showed a pneumomediastinum and a fibrotic interstitial lung disease without dominating ground - glass opacities . bronchoalveolar lavage demonstrated a slightly lymphocytic and neutrophilic alveolitis . after recovering from the pneumomediastinum , pneumomediastinum has been described in other fibrotic lung diseases , but until now it has not been described as a primary manifestation of chronic fibrotic hp . particularly in cases of concurrent antigen sources , chronic hypersensitivity pneumonitis ( hp ) can be grouped into 2 types  recurrent and insidious chronic hp . particularly in insidious chronic hp , patients have no history of acute episodes with typical flu - like symptoms , but instead have slowly progressive chronic respiratory disease . pneumomediastinum , also called mediastinal emphysema , is the presence of free air around mediastinal structures and can be divided in spontaneous pneumomediastinum , without any obvious primary source , and secondary pneumomediastinum , with a specific responsible pathologic event such as trauma , intrathoracic infections or trauma to the aerodigestive tract . until now , pneumomediastinum has only been described in a patient with acute hp   and in a patient with hp during steroid treatment . to the best of the authors knowledge , this is the first report of pneumomediastinum as the primary manifestation of hp in a patient with a well - documented chronic insidious course of farmer s lung . a 45-year - old nonsmoking male was transferred to the fachkrankenhaus coswig centre for respiratory medicine for further investigation and management of pneumomediastinum and interstitial lung disease . he had worked in farming for almost 20 years and was exposed in childhood by his father to pigeon breeding until 20 years ago . he reported dyspnea on exercise and weight loss of 10 kg in the previous 2 years . two days prior to admission at our center , he had complained of chest pain . blood gas analysis showed mild respiratory failure at rest , with a pao2 of 68 mmhg , paco2 of 40 mmhg and ph of 7.44 . specific igg antibodies were highly elevated for different molds , particularly aspergillus fumigatus and moderately elevated for different avian antigens , particularly pigeon antigens and goose feathers . a high - resolution ct scan of the lung ( figure 1 a , b ) demonstrated a marked pneumomediastinum and interstitial lung disease with reticulation in all lobes , but basal predominance , honeycombing , traction bronchiectasis , and mild - to - moderate ground - glass opacities . pulmonary function tests revealed moderate restriction ( tlc 4.5 l [ 59% predicted ] , fvc 3.0 l [ 56% predicted ] , fev1 2.9 l [ 72% predicted ] ) , fev1/fvc 98% , and a diffusion capacity of 2.20 mmol / min / kpa ( 19% predicted ) . flow cytometric analysis of the bal lymphocyte population revealed a cd4/cd8 ratio of 0.5 . because the transbronchial biopsy specimens revealed no conclusive pathological pattern , an open lung biopsy was performed and demonstrated a uip - pattern without any granulomas ( figure 2 ) . after complete resolution of the pneumomediastinum and slight improvement of the lung function with temporary prednisolone therapy for 6 weeks , an inhalative challenge with tossing hay from the workplace over a 1-hour period was performed in a special provocation chamber of the hospital . the inhalative challenge was positive , with systemic and pulmonary reaction 46 hours after stopping the exposure ( figure 3a  d ) . in this report we present a well - documented case of a patient with chronic farmer s lung and a pneumomediastinum as the primary manifestation of the disease . pneumomediastinum results from rupture of the alveoli due to marked increase in intra - alveolar pressure . in patients with interstitial lung diseases , subpleural or paracardiac blebs may form due to the distortion of lung architecture , and the rupture of paracardiac blebs may also lead to air leakage in the mediastinum . in a retrospective analysis of 74 patients with pneumomediastinum , 28 had a spontaneous form and 2 ( 7% ) had an idiopathic pulmonary fibrosis ( ipf ) as a predisposing condition . the frequency of pneumomediastinum in patients with ipf was investigated in a study by franquet et al , who found 4 ( 5% ) pneumomediastinums in 78 patients with confirmed ipf who underwent a computed tomography of the chest . another study found a pneumomediastinum in 5 of 34 patients with pulmonary fibrosis ( 15% ) on computed tomography of the chest . an open lung biopsy revealed a granulomatous inflammation of the lung , resulting in obstruction or narrowing of respiratory bronchioles and emphysematous surrounding alveoli . it was postulated that this obstructive bronchiolitis , which is a common pathologic feature in acute and chronic courses of farmer s lung , assumed an important role in the development of the pneumomediastinum . another case report presented a patient with non - fibrotic chronic farmer s lung complicated by bilateral pneumothorax and mediastinal emphysema under treatment with steroids . the authors postulated that the steroid administration may have caused these complications . in chronic insidious bird fancier s lung , a hypersensitivity pneumonitis caused by avian antigens , honeycombing was observed on hrct scans in most cases . only a mild lymphocytosis was observed in bal fluid , and uip - like lesions could be revealed from surgical lung biopsies . particularly , an inhalative challenge could help to differentiate chronic bird fancier s lung from ilf . in our patient there is therefore no doubt about the diagnosis of chronic farmer s lung , because of the history of farming over nearly 20 years with highly elevated specific igg - antibodies against molds , particularly aspergillus fumigatus , and the positive inhalative hay challenge . in conclusion , pneumomediastinum is a rare complication of interstitial lung diseases . to the best of the authors knowledge , this is the first report of a pneumomediastinum associated with chronic fibrotic hp in a well - documented case of farmer s lung , and particularly as the primary manifestation of the disease .
summarybackgroundpatients with chronic hypersensitivity pneumonitis ( hp ) can present with an insidious onset of their disease without typical fluctuating flu - like symptoms , and there are only signs of chronic respiratory failure caused by the progressive fibrotic lung disease.case reporta 45-year - old man with a pneumomediastinum and interstitial lung disease was referred for further investigations and therapy . 
 no traumatic event or interventional procedure had occurred prior to referral . 
 the patient had been working in farming for almost 20 years and was exposed in childhood by his father to pigeon breeding from childhood until 20 years ago . 
 he reported dyspnea on exercise for the previous 2 years . 
 high - resolution ct of the lung showed a pneumomediastinum and a fibrotic interstitial lung disease without dominating ground - glass opacities . 
 specific igg antibodies were markedly elevated against molds and avian antigens . 
 bronchoalveolar lavage demonstrated a slightly lymphocytic and neutrophilic alveolitis . 
 after recovering from the pneumomediastinum , an open lung biopsy was performed and a uip - pattern was detected . an inhalative challenge with hay from the work - place was positive . 
 a diagnosis of chronic farmer s lung was made.conclusionspneumomediastinum has been described in other fibrotic lung diseases , but until now it has not been described as a primary manifestation of chronic fibrotic hp . particularly in cases of concurrent antigen sources , 
 an inhalative challenge could be done , even in a chronic course of hp .