Hypersensitivity pneumonitis in children: clinical features, diagnosis, and treatment

The Challenging Diagnosis of Interstitial Lung Disease in Children-One Case Report and Literature Review

Childhood interstitial lung disease (chILD) includes a heterogeneous spectrum of rare respiratory disorders in children associated with substantial morbi-mortality. Interstitial tissue, and other pulmonary structures, epithelium, blood vessels, or pleura are involved, resulting in a restrictive lung disfunction. Respiratory symptoms set in progressively and are often subtle, making thorough clinical history and physical examination fundamental. The etiology often is obscure. The clinical presentation mimics pneumonia or asthma, leading to a diagnostic delay. Challenging diagnosis may require genetic tests, bronchoalveolar lavage, or lung biopsy. Alongside general supportive therapeutic measures, anti-inflammatory, immunosuppressive or antifibrotic agents may be used, based on data derived from adult studies. However, if accurate diagnosis and treatment are delayed, irreversible chronic respiratory failure may ensue, impacting prognosis. The most frequent chILD is hypersensitivity pneumonitis (HP), although it is rare in children. HP is associated with exposure to an environmental antigen, resulting in inflammation of the airways. Detailed antigen exposure history and identification of the inciting trigger are the cornerstones of diagnostic. This article provides the current state of chILD, revealing specific features of HP, based on a clinical case report of a patient admitted in our clinic, requiring extensive investigations for diagnosis, with a favorable long-term outcome.

Clinical radiological and pathological staging of children with hypersensitivity pneumonitis

OBJECTIVE

Hypersensitivity pneumonitis (HP) is rare in the pediatric population. To date, there are no studies defining a correlation between clinical, radiological, and pathological findings in children with HP. The objective of this study is to define the clinical, and radiological characteristics and prognosis of childhood HP and to examine the clinical, radiological, and pathological correlation between HP stages.

METHODS

Patients with suspected HP and followed at two tertiary care hospitals between 2000 and 2020 were retrospectively evaluated. Computed tomography (CT) of the chest of patients was evaluated by a single radiologist. The interagreement between clinical and radiological severity of the patients was calculated with the κ test.

RESULTS

Fourteen children with suspected HP were identified. The results of 10 patients with the definitive diagnosis were as follows: one patient (10%) had acute, five patients (50%) had subacute, and four patients (40%) had chronic HP. The most prominent findings in chest CT were hilar, or hilar and subcarinal lymphadenopathy (80%), centrilobular nodules (60%), patchy or diffuse ground-glass opacities (50%), and cysts (50%). The interagreement between clinical and radiological severity of the patients was 100% (approximate significance: 0.003). The diagnosis of four patients with suspected HP who were unresponsive to standardized medical treatments or developed multisystem involvement was diagnosed with other diseases. One patient (10%) with definitive chronic HP died due to respiratory failure during follow up.

CONCLUSION

Similar to adult HP, the prognosis is worse in children with existing fibrotic equivalents in chest CT. Patients who are not responding to standard medical treatments or develop multisystem involvement should be evaluated for other lung diseases.

Interstitial lung disease in infancy and early childhood: a clinicopathological primer

Children's interstitial lung disease (chILD) encompasses a wide and heterogeneous spectrum of diseases substantially different from that of adults. Established classification systems divide chILD into conditions more prevalent in infancy and other conditions occurring at any age. This categorisation is based on a multidisciplinary approach including clinical, radiological, genetic and histological findings. The diagnostic evaluation may include lung biopsies if other diagnostic approaches failed to identify a precise chILD entity, or if severe or refractory respiratory distress of unknown cause is present. As the majority of children will be evaluated and diagnosed outside of specialist centres, this review summarises relevant clinical, genetic and histological findings of chILD to provide assistance in clinical assessment and rational diagnostics.

ILD of childhood is comparable by name only to lung disease in adults. A dedicated interdisciplinary team is required to achieve the best possible outcome. This review summarises the current clinicopathological criteria and associated genetic alterations.https://bit.ly/3mpxI3b

Pediatric hypersensitivity pneumonitis: literature update and proposal of a diagnostic algorithm

Hypersensitivity pneumonitis (HP) is a rare disease in childhood with the prevalence of 4 cases per 1 million children and an incidence of 2 cases per year. The average age of diagnosis at pediatric age is approximately 10 years. The pathogenesis of HP is characterized by an immunological reaction caused by recurrent exposure to triggering environmental agents (mostly bird antigens in children). The clinical picture of HP is complex and variable in children, often presenting in subacute forms with cough and exertion dyspnea. A diagnosis of HP should be considered in patients with an identified exposure to a triggering antigen, respiratory symptoms, and radiologic signs of interstitial lung disease. Blood tests and pulmonary function tests (PFT) support the diagnosis. Bronchoscopy (with bronchoalveolar lavage and tissue biopsy) may be needed in unclear cases. Antigen provocation test is rarely required. Of note, the persistence of symptoms despite various treatment regimens may support HP diagnosis. The avoidance of single/multiple triggers is crucial for effective treatment. No evidence- based guidelines for treatment are available; in particular, the role of systemic glucocorticoids in children is unclear. With adequate antigen avoidance, the prognosis in children with HP is generally favorable.

Hypersensitivity pneumonitis: Lessons from a randomized controlled trial in children

INTRODUCTION

Hypersensitivity pneumonitis (HP) in children is a severe interstitial lung disease and potentially, a chronic condition, if not treated appropriately. No evidence-based guidelines are available; in particular, the role of systemic glucocorticoid therapy is unclear.

METHODS

The aim of this randomized, double-blind, placebo-controlled, parallel-group, multi-center, phase II trial in pediatric HP was to assess the outcome of HP in children after 6 months of treatment and to compare 3 months of treatment with oral prednisolone or placebo.

RESULTS

After 1.5 years and the inclusion of only four children, we terminated the study prematurely. Two of the children randomized to prednisolone did not achieve the predefined response of FVC to normal. One child treated with placebo recovered to normal, similar to another child treated with prednisolone. All children treated with steroids developed drug-related side effects.

DISCUSSION

This uncompleted study illustrates the urgent medical need for evidence-based treatment protocols for this condition. We discuss the hurdles which were specific for completion of this trial in a rare condition. Among other options, we suggest the inclusion of children into an all-age study of HP, as in adults the same questions are unanswered.

Clinical Features of Hypersensitivity Pneumonitis in Children: A Single Center Study

BACKGROUND

Hypersensitivity pneumonia (HP) is an interstitial lung disease (ILD) mainly involving small airways and lung parenchyma that is caused by the inhalation of antigens in susceptible people to stimulate the body's immune response.

METHODS

A total of 6 Chinese children with HP treated in our center from July 2017 to July 2021 were included in our study.

RESULTS

Among the children, there were 4 males and 2 females, ranging in age from 4 to 14 years. Three cases had chest tightness and shortness of breath, 2 cases had cough, 1 case had chest pain, and 1 case had fever. Two cases of children had a history of close contact with pet dogs, 1 case had a history of contact with pigeons, 2 cases lived in a moldy house recently, and 1 case recently played a saxophone that had been idle for more than 2 years. The parents of two cases also had similar symptoms recently. The specific signs of chest HRCT of 6 cases all were in line with the characteristics of HP. After avoiding the sensitization environment, 2 children quickly recovered, 4 patients received low-dose glucocorticoid oral treatment, and after symptom control the dose was gradually reduced. The course of treatment was about 3-6 months.

CONCLUSIONS

Exposure to a potential antigen has been found in all 6 HP children. The clinical manifestations are heterogeneous and easy to confuse with other diseases. A clear history of exposure to the antigens, respiratory symptoms associated with HP, signs of HP on HRCT, and improvement after removal from the antigenic environment constitute the cornerstone of the diagnosis of HP children in our unit. Avoiding exposure to antigenic environment is the first step in treatment, and glucocorticoid use is necessary in children with persistent symptoms.

[Bird fancier's disease in a child: about a rare and unusual case]

La pathologie du poumon des éleveurs d´oiseaux fait partie des pneumopathies d´hypersensibilité, elle est secondaire à une réaction immuno-allergique aux antigènes aviaires. Cette entité demeure rare chez l´enfant. Elle constitue les deux tiers des pneumopathies d´hypersensibilité. Le diagnostic de cette maladie n´est pas si aisé. Il repose sur un faisceau d´arguments. Nous rapportons une observation singulière d´une fille de 7 ans, ayant comme antécédent un terrain d´atopie familiale, traitée initialement comme asthme devant des épisodes de dyspnée sifflante et une toux sans amélioration. La symptomatologie s´est aggravée par l´installation d´une dyspnée au repos, compliquée d´une détresse respiratoire cyanosante dans un contexte d´altération de l´état général. L´examen clinique a retrouvé un enfant ayant un retard pondéral, une cyanose péribuccale avec un hippocratisme digital. L´auscultation pulmonaire a objectivé des râles crépitants bilatéraux. La radiographie du thorax a mis en évidence un syndrome interstitiel bilatéral. La tomodensitométrie (TDM) thoracique a montré un aspect en verre dépoli diffus. Le bilan biologique a révélé une hyperéosinophilie avec une hyper-IgE, et a écarté une tuberculose, une mucoviscidose, un déficit immunitaire. La reprise de l´interrogatoire a montré un contact avec les oiseaux. Les sérologies de la maladie du poumon des éleveurs d´oiseaux étaient positives. La patiente est mise sous corticothérapie inhalée avec éviction de l´expositions aux oiseaux. Après un recul de 2 mois, l´évolution était favorable. Etant donné que les signes de la maladie du poumon des éleveurs d´oiseaux sont non spécifiques, elle doit être évoquée devant toute symptomatologie respiratoire avec la notion de contact aux antigènes aviaires.

Interstitial lung diseases in children

Interstitial lung disease (ILD) in children (chILD) is a heterogeneous group of rare respiratory disorders that are mostly chronic and associated with high morbidity and mortality. The pathogenesis of the various chILD is complex and the diseases share common features of inflammatory and fibrotic changes of the lung parenchyma that impair gas exchanges. The etiologies of chILD are numerous. In this review, we chose to classify them as ILD related to exposure/environment insults, ILD related to systemic and immunological diseases, ILD related to primary lung parenchyma dysfunctions and ILD specific to infancy. A growing part of the etiologic spectrum of chILD is being attributed to molecular defects. Currently, the main genetic mutations associated with chILD are identified in the surfactant genes SFTPA1, SFTPA2, SFTPB, SFTPC, ABCA3 and NKX2-1. Other genetic contributors include mutations in MARS, CSF2RA and CSF2RB in pulmonary alveolar proteinosis, and mutations in TMEM173 and COPA in specific auto-inflammatory forms of chILD. However, only few genotype-phenotype correlations could be identified so far. Herein, information is provided about the clinical presentation and the diagnosis approach of chILD. Despite improvements in patient management, the therapeutic strategies are still relying mostly on corticosteroids although specific therapies are emerging. Larger longitudinal cohorts of patients are being gathered through ongoing international collaborations to improve disease knowledge and targeted therapies. Thus, it is expected that children with ILD will be able to reach the adulthood transition in a better condition.

[Hypersensitivity pneumonitis in children]

Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by an immune response to a variety of antigens to which patients have been previously sensitised. It can occur at any age. In children, it is a rare disease, probably under-diagnosed, with an estimated prevalence of 4 per million. The paediatric forms are not really different from those of adults but present some particularities. Avian exposure is by far the most frequent cause of HP, accounting for nearly two-thirds of cases. Although there is no current recommendation for the diagnosis of HP, it is commonly considered that the diagnosis can be made with confidence on the combination of (1) compatible respiratory symptoms, (2) exposure to a known offending antigen, (3) lymphocytic alveolitis, (4) decreased transfer factor for carbon monoxide or hypoxia on exertion and (5) compatible radiologic features. The treatment is based on antigen avoidance that must be complete and definitive. Corticosteroids can be necessary in severe forms. The prognosis of HP in children is better than in adults, with a full clinical and functional recovery in the majority of cases after complete antigenic withdrawal.

A Rare Pediatric Case of Severe Bird Fancier's Lung Presented with Viral Pneumonitis-Like Picture

Bird Fancier's Lung (BFL) is a rare, nonatopic immunologic response to repeated or intense inhalation of avian (bird) proteins/antigens found in the feathers or droppings of many species of birds, which leads to an immune-mediated inflammatory reaction in the respiratory system. Although this is the most common type of hypersensitivity pneumonitis (HP) reported in adults, it is one of the classifications of a rare subtype of interstitial lung disease that occurs in the pediatric age group of which few case reports are available in the literature. The pathophysiology of HP is complex; numerous organic and inorganic antigens can cause immune dysregulation, leading to an immune-related antigen⁻antibody response (immunoglobulin G-IgG- against the offending antigen). Diagnosing BFL in the pediatric age group is challenging due to the history of exposure usually being missed by health care providers, symptoms and clinical findings in such cases being nonspecific and often misdiagnosed during the acute illness with other common diseases such asthma or acute viral lower respiratory tract infection, and the lack of standardization of criteria for diagnosing such a condition or sensitive radiological or laboratory tests. Treatment, on the other hand, is also controversial. Avoidance of the offending antigen could be the sole or most important part of treatment, particularly in acute mild and moderate cases. Untreated cases can result in irreversible lung fibrosis. In this case report, we highlight how children presenting with an acute viral lower respiratory tract infection can overlap with the acute/subacute phase of HP. Early intervention with pulse steroids markedly improves the patient's clinical course.

Chronic interstitial lung diseases in children: diagnosis approaches

Introduction: Children interstitial lung disease (chILD) is a heterogeneous group of rare respiratory disorders characterized by inflammatory and fibrotic changes of the lung parenchyma. They include ILD related to exposure/environment insults, ILD related to systemic diseases processes, ILD related to primary lung parenchyma dysfunctions and ILD specific to infancy. Areas covered: This review provides an update on chILD pathophysiology and diagnosis approaches in immunocompetent children. It includes current information on genetic causes. Expert commentary: ChILD covers a large spectrum of entities with heterogeneous disease expression. Various classifications have been reported, but none of them seems completely satisfactory. Recently, progress in molecular genetics has allowed identifying some genetic contributors, with, so far, a lack of correlations between gene disorders and disease expression. Despite improvements in patient management, chILD prognosis is still burdened by significant morbidity and mortality. Ongoing international collaborations will allow gathering larger longitudinal cohorts of patients to improve disease knowledge and personalized care. The overall goal is to help the children with ILD to reach the adulthood transition in a better condition, and to structure genetic counseling for their family.

Mimicking hypersensitivity pneumonitis as an uncommon initial presentation of chronic granulomatous disease in children

Dry cough, dyspenea and diffuse centrilobular nodules in both lungs of radiologic findings similar to hypersensitivity pneumonitis (HP) are rare initial presentation in chronic granulomatous disease (CGD). CGD is remarkable for increased susceptibility to bacterial and fungal infections as well as high sensitivity to inciting antigens such as Aspergillus species due to dysregulated inflammation. We identified three children who had an initial presentation mimicking HP and were subsequently diagnosed as CGD. All patients developed invasive pulmonary A. fumigatus infection (IPAI) following systemic glucocorticoid therapy. Two of the three patients were found to have mutations in NCF1 gene and one patient in NCF2 gene. As HP is uncommon in children, we should consider the possibility of CGD in children with HP, even in mimicking HP patients with suggestive inhalation history and negative fungal cultures. A prompt diagnosis of CGD is essential to enable initiation of prophylactic antibacterial and antifungal therapies.

An unusual radiologic manifestation of hypersensitivity pneumonia

Hypersensitivity pneumonia is clinically suspected and can be characterized on computed tomography by its pattern of diffuse lung disease, in children, as in adults. However, identifying the diagnosis is not always as simple. We report an organizing pneumonia pattern of hypersensitivity pneumonia that can be seen in adult patients, but has not been reported in the pediatric population.

Interstitial Lung Disease in Childhood: Clinical and Genetic Aspects

Interstitial lung disease (ILD) in childhood is a heterogeneous group of rare pulmonary conditions presenting chronic respiratory disorders. Many clinical features of ILD still remain unclear, making the treatment strategies mainly investigative. Guidelines may provide physicians with an overview on the diagnosis and therapeutic directions. However, the criteria used in different clinical studies for the classification and diagnosis of ILDs are not always the same, making the development of guidelines difficult. Advances in genetic testing have thrown light on some etiologies of ILD, which were formerly classified as ILDs of unknown origins. The need of genetic testing for unexplained ILD is growing, and new classification criteria based on the etiology should be adopted to better understand the disease. The purpose of this review is to give an overview of the clinical and genetic aspects of ILD in children.

Application of clinico-radiologic-pathologic diagnosis of diffuse parenchymal lung diseases in children in China

Diffuse parenchymal lung diseases in children (chDPLD) or interstitial lung diseases in children (chILD) represent a heterogeneous group of respiratory disorders that are mostly chronic and associated with high morbidity and mortality. However, the incidence of chDPLD is so low that most pediatricians lack sufficient knowledge of chDPLD, especially in China. Based on the clinico-radiologic-pathologic (CRP) diagnosis, we tried to describe (1) the characteristics of chDPLD and (2) the ratio of each constituent of chDPLD in China. Data were evaluated, including clinical, radiographic, and pathologic results from lung biopsies. We collected 25 cases of chDPLD, 18 boys and 7 girls with a median age of 6.0 years, from 16 hospitals in China. The most common manifestations included cough (n = 24), dyspnea (n = 21), and fever (n = 4). There were three cases of exposure-related interstitial lung disease (ILD), three cases of systemic disease-associated ILD, nineteen cases of alveolar structure disorder-associated ILD, and no cases of ILD specific to infancy. Non-specific interstitial pneumonia (n = 9) was the two largest groups.

CONCLUSION

Non-specific interstitial pneumonia is the main categories of chDPLD in China. Lung biopsy is always a crucial step in the final diagnosis. However, clinical and imaging studies should be carefully evaluated for their value in indicating a specific chDPLD.

Interstitial lung disease in children

Children's interstitial lung disease (ILD) includes a wide range of rare respiratory disorders associated with high morbidity and mortality. Genetic factors, systemic disease processes, nonspecific inflammatory or fibrotic patterns of repair seen in a number of clinical settings are involved in the ILD pathogenesis. Specific disorders more prevalent in young children include diffuse developmental disorders, alveolar growth abnormalities, genetic surfactant disorders, pulmonary interstitial glycogenosis and neuroendocrine cell hyperplasia of infancy. It may be difficult to recognize these entities and this can lead to delayed treatment. The diagnostic approach is based on a combination of history/physical examinations, imaging studies, pulmonary function testing, genetic testing, bronchoalveolar lavage (BAL) and in most cases an open lung biopsy. Although some disease types overlap with those seen in adults, in this review emphasis is placed on entities unique to the pediatric population focusing on clinical characteristics, histologic definitions, radiologic-pathologic correlation and therapeutic strategies.

Respiratory and allergic health effects of dampness, mold, and dampness-related agents: a review of the epidemiologic evidence

OBJECTIVES

Many studies have shown consistent associations between evident indoor dampness or mold and respiratory or allergic health effects, but causal links remain unclear. Findings on measured microbiologic factors have received little review. We conducted an updated, comprehensive review on these topics.

DATA SOURCES

We reviewed eligible peer-reviewed epidemiologic studies or quantitative meta-analyses, up to late 2009, on dampness, mold, or other microbiologic agents and respiratory or allergic effects.

DATA EXTRACTION

We evaluated evidence for causation or association between qualitative/subjective assessments of dampness or mold (considered together) and specific health outcomes. We separately considered evidence for associations between specific quantitative measurements of microbiologic factors and each health outcome.

DATA SYNTHESIS

Evidence from epidemiologic studies and meta-analyses showed indoor dampness or mold to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and nonallergic individuals. Evidence strongly suggested causation of asthma exacerbation in children. Suggestive evidence was available for only a few specific measured microbiologic factors and was in part equivocal, suggesting both adverse and protective associations with health.

CONCLUSIONS

Evident dampness or mold had consistent positive associations with multiple allergic and respiratory effects. Measured microbiologic agents in dust had limited suggestive associations, including both positive and negative associations for some agents. Thus, prevention and remediation of indoor dampness and mold are likely to reduce health risks, but current evidence does not support measuring specific indoor microbiologic factors to guide health-protective actions.

Interstitial lung diseases in children

Interstitial lung disease (ILD) in infants and children comprises a large spectrum of rare respiratory disorders that are mostly chronic and associated with high morbidity and mortality. These disorders are characterized by inflammatory and fibrotic changes that affect alveolar walls. Typical features of ILD include dyspnea, diffuse infiltrates on chest radiographs, and abnormal pulmonary function tests with restrictive ventilatory defect and/or impaired gas exchange. Many pathological situations can impair gas exchange and, therefore, may contribute to progressive lung damage and ILD. Consequently, diagnosis approach needs to be structured with a clinical evaluation requiring a careful history paying attention to exposures and systemic diseases. Several classifications for ILD have been proposed but none is entirely satisfactory especially in children. The present article reviews current concepts of pathophysiological mechanisms, etiology and diagnostic approaches, as well as therapeutic strategies. The following diagnostic grouping is used to discuss the various causes of pediatric ILD: 1) exposure-related ILD; 2) systemic disease-associated ILD; 3) alveolar structure disorder-associated ILD; and 4) ILD specific to infancy. Therapeutic options include mainly anti-inflammatory, immunosuppressive, and/or anti-fibrotic drugs. The outcome is highly variable with a mortality rate around 15%. An overall favorable response to corticosteroid therapy is observed in around 50% of cases, often associated with sequelae such as limited exercise tolerance or the need for long-term oxygen therapy.

Interstitial Lung Disease in Children Older Than 2 Years

The spectrum of childhood interstitial lung diseases (chILD) encompasses a group of heterogeneous, rare disorders in children characterized by diffuse pulmonary infiltrates and disordered gas exchange. Whereas the disorders that present in early life are unique to children, those that present in older children are also seen in adults. This review will concentrate on chILD presenting in children older than 2 years of age with a focus on the idiopathic interstitial pneumonias, connective tissue diseases, alveolar hemorrhage, and hypersensitivity pneumonitis. A systematic approach to diagnosis that includes a careful history and physical, computed tomography of the chest, bronchoalveolar lavage, and lung biopsy can be very helpful in establishing the correct diagnosis. Treatment approaches are described, including general supportive measures, indications for a trial of systemic corticosteroids, or other immunomodulating therapies, and when lung transplantation reserved for those with end-stage lung disease should be considered.

Bird fancier's lung: a series of 86 patients

Bird fancier's lung (BFL) is one of the most common types of hypersensitivity pneumonitis. Nevertheless, the criteria for diagnosing this condition are not standardized. The current study is an in-depth investigation into the clinical characteristics of BFL in the largest series examined for this purpose by a single group, to our knowledge, taking into account the acute, subacute, or chronic clinical presentation. From 1977 to 2003, BFL was diagnosed in 86 patients using a homogeneous protocol. Data from the clinical history and physical examination were analyzed, as well as the results from the following complementary examinations: laboratory analyses, specific serum IgG antibodies determination, chest X-ray, chest computed tomography (CT), pulmonary function testing, immediate hypersensitivity skin testing, delayed cutaneous hypersensitivity testing, bronchofibroscopy with bronchoalveolar lavage (BAL) and/or transbronchial biopsy, bronchial challenge testing, and surgical lung biopsy. In addition, clinical and epidemiologic characteristics were determined in a control group of 60 pigeon breeders who did not meet the diagnostic criteria of BFL. Eighty-six patients (21 men and 65 women) with a mean age of 47 years were studied. Seven (8%) patients were younger than 15 years of age at the time of the diagnosis. In 3 cases, the disease was caused by exposure to feather-filled bedding. Nearly 1 in 5 patients was diagnosed in the chronic phase of the disease. The mean diagnostic delay was 1.6 years overall, and 3.2 years in patients diagnosed in the chronic phase of the disease. Among the 17% of patients with chronic disease, the mean interval from initiation of exposure to diagnosis was 16 years, a higher value than in the acute or subacute presentation forms. Dyspnea and cough were the most common clinical symptoms (98% and 82%, respectively), and nearly 25% had grade III or IV dyspnea at diagnosis. Only 18% of patients experienced chest tightness, a symptom classically considered to be frequent in this condition. Erythrocyte sedimentation rate was elevated (>30 mm/h) in 44% of patients. Urinary calcium was elevated in 20% of patients. Angiotensin-converting enzyme was not elevated in any of the patients in which it was measured. Lactate dehydrogenase increases were found in 51% of patients. Specific IgG antibodies to avian antigens were documented in 92% of BFL patients, but also in 87% of pigeon breeder controls. The most frequent radiologic finding was an interstitial pattern in 79% of patients. Common chest CT features were ground glass areas (68%) and a mosaic pattern (61%); areas of emphysema were found in 7/41 (17%) patients, 5 of whom had never smoked. Two patients had a CT pattern of pulmonary fibrosis indistinguishable from idiopathic pulmonary fibrosis. Immediate hypersensitivity skin testing with bird sera and pigeon bloom was positive in 78% and 100% of BFL patients, respectively, and in 64% and 88% of control pigeon breeders, respectively. Almost one-third of the patients (29%) presented an anergic response on delayed cutaneous hypersensitivity testing. Restrictive ventilatory impairment was the most frequent functional pattern (77%), although 9% and 4% showed a pure obstructive and mixed pattern, respectively. The carbon monoxide diffusing capacity was decreased (<80% of the predicted value) in 85% of cases. Forty-one percent of patients had PaO2 <60 mm Hg at diagnosis when blood gas analysis was performed. Lymphocytosis (>20% lymphocytes) was documented in 83% of patients who underwent BAL, with a similar frequency in the 3 presentation forms: 70% acute, 89% subacute, and 85% chronic. In addition, inversion of the CD4/CD8 ratio (<1) was observed in 62% of the patients, but 38% of cases showed a CD4 predominance. The characteristic triad of histopathologic findings in hypersensitivity pneumonitis was found in only 9% of patients undergoing transbronchial biopsy, but at least 1 of these findings was seen in 69%. Surgical lung biopsy was undertaken in 14/86 (16%) patients; the complete triad was observed in 50% and at least 1 finding in 100%. In 54/86 (63%) patients, the diagnosis was confirmed by bronchial challenge testing, a test with a sensitivity of 92% and specificity of 100%. BFL is a potentially severe disease that can progress to respiratory failure secondary to pulmonary fibrosis or chronic obstructive pulmonary disease, as a form of chronic occupational respiratory disease. Respiratory symptoms in exposed patients, including children and adults who have only 1 pet bird at home, should raise the suspicion of BFL. Diagnosis in the chronic phase is frequent, and the delay to diagnosis was greatest in these cases. Elevated urinary calcium, lactate dehydrogenase, and erythrocyte sedimentation rate in a bird fancier may constitute a combined marker for suspected BFL. Chest CT frequently discloses emphysema and a pattern of idiopathic pulmonary fibrosis in some patients. An anergic response on delayed cutaneous hypersensitivity testing is not infrequent. The presentation with respiratory failure and the predominance of CD4 T lymphocytes in some patients' BAL are both remarkable. Lymphocytosis on BAL also persists in the chronic phase of the disease. Bronchial challenge testing has a high diagnostic yield, and surgical lung biopsy is not needed to reach the final diagnosis in the vast majority of cases.