Respiratory · Year 1 · from Respiratory
Case 3: Hypersensitivity Pneumonitis from Bird Exposure
Case Presentation
A 55-year-old woman presents with progressive dyspnea and cough over 6 months. She notes that symptoms improve when she travels but worsen upon returning home. Detailed history reveals she has kept parakeets as pets for the past 3 years. On examination, she has fine inspiratory crackles throughout both lung fields. Oxygen saturation is 92% on room air.
Pulmonary function tests show FEV1 1.8 L (68% predicted), FVC 2.0 L (62% predicted), FEV1/FVC 0.90, TLC 3.5 L (58% predicted), and DLCO 52% predicted. The pattern is restrictive with reduced diffusing capacity. High-resolution CT chest shows diffuse ground-glass opacities, mosaic attenuation (areas of air trapping from small airway involvement), and centrilobular nodules - a pattern consistent with subacute hypersensitivity pneumonitis.
Bronchoalveolar lavage reveals lymphocytosis (55% lymphocytes, normal less than 15%) with a CD4/CD8 ratio of 0.6 (decreased, in contrast to sarcoidosis which shows elevated ratio). Serum precipitins to avian proteins are positive.
The diagnosis is bird fancier's lung, a form of hypersensitivity pneumonitis caused by immune-mediated reaction to avian proteins (found in droppings and feathers). The pathophysiology involves a combined type III (immune complex) and type IV (cell-mediated) hypersensitivity reaction in sensitized individuals.
The cornerstone of treatment is antigen avoidance - the patient rehomes her birds and undergoes professional cleaning of her home to remove accumulated avian proteins. She is started on a tapering course of prednisone given her significant functional impairment. At 3-month follow-up, her symptoms have markedly improved, DLCO has increased to 72% predicted, and CT shows resolution of ground-glass opacities. Had she continued exposure, she would have been at risk for progression to chronic fibrotic disease resembling IPF.
Key Learning Points
- Hypersensitivity pneumonitis is an immune-mediated reaction to inhaled organic antigens
- Detailed exposure history is critical - symptoms improving away from home/work is a key clue
- CT findings include ground-glass opacities, mosaic attenuation, and centrilobular nodules
- BAL shows lymphocytosis with low CD4/CD8 ratio (opposite of sarcoidosis)
- Antigen avoidance is essential; continued exposure leads to irreversible fibrosis