Surgical Pathology Criteria

Hypersensitivity Pneumonitis

Differential Diagnosis

In all cases, infectious organisms, especially fungi and mycobacteria must be ruled out

Usual Interstitial Pneumonia Hypersensitivity Pneumonitis
Lacks granulomas and giant cells Granulomas and giant cells generally present but may be infrequent in late stage
Random distribution Usually has some component of bronchiolocentric distribution even in late stage

 

Hypersensitivity Pneumonitis Nonspecific Interstitial Pneumonia
Usually has some component of bronchiolocentric distribution even in late stage Diffuse interstitial inflammation
Granulomas and giant cells generally present but may be infrequent in late stage No granulomas or giant cells
Some cases progress to honeycomb change, others may have fibrosis indistinguishable from NSIP Fibrosis usually diffuse and preserves architecture
These may at times be indistinguishable

 

Lymphocytic Interstitial Pneumonitis Hypersensitivity Pneumonitis
Diffuse involvement of alveolar septa Predominantly peribronochiolar
Marked infiltrate Patchy, less dense infiltrate
No BOOP-like foci BOOP-like foci common
Both may have loose granulomas and develop honeycomb change

 

Respiratory Bronchiolitis Associated Interstitial Lung Disease Hypersensitivity Pneumonitis
Lacks granulomas and giant cells Granulomas and giant cells generally present but may be infrequent in late stage
Smoking history only Possible exposure history
May develop mild-moderate peri-bronchiolar fibrosis but architecture is preserved May develop significant fibrosis with honeycomb change

 

Follicular Bronchiolitis Hypersensitivity Pneumonitis
Fibroplasia is not typically seen Interstitial fibroblastic foci and intra-airway BOOP-like plugs usually present
No granulomas or giant cells Granulomas and giant cells generally present but may be infrequent in late stage
No fibrosis May develop peri-bronchiolar fibrosis with honeycomb change in later stage

 

Langerhans Cell Histiocytosis Hypersensitivity Pneumonitis
Lacks granulomas and giant cells Granulomas and giant cells generally present but may be infrequent in late stage
Smoking history only Possible exposure history
CD1a and langerin positive Langerhans cells present No Langerhans cells
Late fibrotic stage may be impossible to separate if active foci cannot be found

 

Sarcoidosis Hypersensitivity Pneumonitis
Tight, well formed granulomas Loose, poorly formed granulomas
Usually mild, at most moderate inflammation Prominent inflammation
No history of allergen exposure May have history of allergen exposure

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