RESIDENT CASE STUDIES

Week 6 May 26 - May 30, 2003: Case 4  

Table of Contents | List of Diagnoses | Case 1 | Case 2 | Case 3 | Case 4

39 year old female with dyspnea and micronodular interstitial pattern in lower/mid lower zones on chest x-ray 

Discussion: 
Hypersensitivity pneumonitits is a diffuse interstitial granulomatous lung disease that represents an immunologic reaction to inhaled organic antigens or chemicals. Most patients experience mild or subclinical symptoms which escape detection, or are misdiagnosed as a viral illness or asthma. The pathogenesis involves a combination of immune complex-mediated Type III hypersensitivity reactions which creates early changes that are combined with a T cell-mediated delayed Type IV hypersensitivity reaction due to antigen exposure that is responsible for granuloma formation. The disease progression results in a restrictive defect and mild hypoxia. 

Histologically, hypersensitivity pneumonitis can be divided into acute, subacute and chronic phase.

Acute Histology - neutrophils infiltrate in alveoli and respiratory bronchioles with temporally uniform non-specific chronic interstitial pneumonia.

Subacute - lymphocytic interstitial pneumonitis with granulomas, organizing pneumonia and fibrosis.

Chronic - “Cellular chronic bronchiolitis with peribronchiolar interstitial inflammation” 

• with bronchiolocentric cellular interstitial pneumonia

• with an inflammatory infiltrate of lymphocytes

• with some plasma cells and histiocytes 

• Eosinophils are rare or absent noncaseating granulomas that are centered on distal airways

• Intraluminal budding fibrosis or organizing pneumonia – polypoid plugs of loose, organizing connective tissue that protrude into the lumens of alveolar ducts and bronchioles; progression into a nonspecific end-stage fibrosis which is irreversible. 

The differential diagnosis a granulomatous interstitial pneumonia is quite broad: sarcoidosis, diffuse granulomatous infections (e.g. with acid fast or fungal organisms), or hypersensitivity pneumonitis. Careful attention to the anatomic distribution of the granulomas, the qualitative features of the granulomas, and the histologic changes in the lung tissue around and away from the granulomas, will help in arriving at the correct diagnosis.³ Cultures results: special stains for micro-organisms (especially, for fungal and mycobacterial organisms). Clinical and radiologic correlation are also necessary to help arrive at the correct diagnosis in the vast majority of cases. 

Other differential diagnosis of hypersensitivity pneumonitis include other interstitial lung diseases like lymphocytic interstitial pneumonia (LIP), usual interstitial pneumonitis (UIP), desquamative interstitial pneumonitis (DIP). However, these are not usually associated with granulomas .

References:

¹Patchefsky A. Nonneoplastic pulmonary disease. In: Sternberg S ed. Diagnostic Surgical Pathology 3^rd edition. Philadelphia. Lippincott Williams and Wilkins, 1999:1013-1023.

²King D ed. Diffuse parenchymal lung diseases. In: Non-neoplastic disorders of the lower respiratory tract. Washington D.C. American Registry of Pathology and the Armed Forces Institute of Pathology, 2002:115-123.