Pigeon breeder's lung is a form of hypersensitivity pneumonitis, which is caused by repetitive exposure to pigeon antigen. The clinical manifestations are classified according to the phase, which is acute, subacute, or chronic. The diagnosis is based on the clinical picture, environmental and patient history, physical exam, and the appropriate studies.
Pigeon breeder's lung (PBL) is an extrinsic allergic alveolitis secondary to inhalation of pigeon antigen . Specifically, this ailment stems from persistent exposure to droppings as well as feather and serum proteins of pigeons and other birds. Hypersensitivity pneumonia is frequently caused by avian antigens , which emerge from both domestic exposure  and the global poultry handling industry.
The clinical presentation of symptomatic hypersensitivity pneumonitis is characterized as acute, subacute, or chronic, which is associated with symptoms of differing intensity and timing  . Acute cases develop hours post exposure and resolve hours to days after withdrawal of exposure. Patients will experience fever, cough, headache, dyspnea, malaise, and chills. The subacute disease is characterized by an insidious onset that may take weeks to months, in which there is a progressive cough, shortness of breath and possibly anorexia. Chronic manifestations of this condition include fatigue, persistent cough, worsening dyspnea, anorexia, and weight loss . Patients with pigeon breeder's lung do not respond to anti-asthma therapy.
Vital signs in acute episodes are notable for fever, tachycardia, tachypnea, and oxygen desaturation . The lung exam may be remarkable for use of accessory muscles. Findings on auscultation may include bibasilar crackles.
In addition to evaluation of the clinical picture, diagnosis of pigeon breeder's lung is achieved by assessing the patient's environmental exposures , detailed history, physical exam, and the appropriate studies. It is also important to rule out differential diagnoses such as tuberculosis, sarcoidosis, connective tissue diseases, mycoplasma, allergic bronchopulmonary aspergillosis, Langerhans cell histiocytosis, malignancies and others   .
Some authors argue that a diagnosis is achieved by demonstration of specific antibodies, a positive skin prick test, and cessation of symptoms following the withdrawal of exposure  .
High-resolution CT (HRCT) scanning in acutely ill patients displays ground-glass opacities that are particularly observed in the lower lobes . In the chronic phase, HRCT displays fibrotic changes, centrilobular nodular lesions, honeycombing, traction bronchiectasis, ground glass attenuation, and irregular linear opacities   .
Pulmonary function tests are important components of the workup. Acute cases will demonstrate a restrictive pattern in which the total lung capacity and forced vital capacity are diminished. Chronic disease is associated with either a restrictive or a mixed picture with both obstructive and restrictive pattern.
Additionally, the diffusing capacity of lungs for carbon monoxide (DLCO) is decreased . The inhalation challenge is another test in which the patient is exposed to the offending agent for confirmation.
Cytology on specimens from bronchoalveolar lavage (BAL) may be inconclusive  but will typically display lymphocytosis . A lung biopsy is not necessary, but findings such as foamy histiocytes from interstitial and alveolar samples are consistent with hypersensitivity pneumonia  .