Pulmonary Pathology Online
Pathology of Lymphocytic Interstitial Pneumonia/Follicular Bronchiolitis
The term "lymphocytic interstitial pneumonia" was introduced by Leibow and Carrington to describe a diffuse lymphocytic infiltrate.
Follicular bronchitis/ bronchiolitis was a term that was introduced to describe a predominantly peribronchial lymphocytic infiltrate with abundant germinal centres.
Lymphocytic interstitial pneumonia (LIP) and follicular bronchiolitis (FB) represent overlapping histological patterns caused by a response of the pulmonary immune system to variety of unknown factors , with lymphoid hyperplasia the underlying pathogenic mechanism in both conditions.
Average age at presentation is about 50 years in both conditions.
These are more common in females.
There is an association with connective tissue disorders, and immunodeficiency.
LIP alone is reported to carry a low risk of lymphomatous transformation.
Presenting symptoms include dyspnoea, cough, recurrent upper respiratory tract infections and chest pain,with haemoptysis in some cases.
In LIP: The main feature is an interstitial infiltrate of small lymphocyte, plasma cells and histiocytes .
Germinal centers are identified in a number of cases.
Granuloma formation is sometimes noted.
In FB: There are abundant peribronchiolar germinal centers and the airway lumen is often compressed.
Most cases show extension of a mixed lymphoid infiltrate into the interstitium, emphasizing the overlap between the two conditions.
Shows that in LIP, CD20-positive B-cells are mainly limited to the germinal centers, whilst the interstitial lymphocytes are predominantly T-cells mixed with plasma cells.
Amplification of the immunoglobulin heavy chain gene using polymerase chain reaction has shown a polyclonal pattern in both FB and LIP.
Visit: Pulmonary Lymphoproliferative Disease ; Idiopathic Pulmonary Fibrosis ; Usual Interstitial Pneumonia (UIP) ; Non-specific interstitial pneumonia (NSIP) ; Respiratory bronchiolitis-interstitial lung disease (RBILD) ; Acute interstitial pneumonia (AIP)/organizing diffuse alveolar damage DAD); Lymphocytic Interstitial Pneumonia / Follicular Bronchiolitis .
Differential Diagnosis :
It is usually difficult to distinguish lymphoid hyperplasia (LIP / FB) from low-grade lymphoma in small biopsies.
Clinical and imaging data may be required to favour one diagnosis or the other.
Biopsy is often required to confirm the diagnosis.
Histopathologically, lymphoma infiltrates and destroy the alveolar architecture more than LIP.
There is greater widening of alveolar septa by the lymphoid infiltrate.
Lymphoepithelial lesions are less frequently seen.
Immunohistochemistry : B-cells tend to infiltrate widely in lymphomas. This is an useful distinguishing factor.
The pattern of a reactive infiltrate is of aggregated B-cells that are usually peribronchial or septal in distribution, with a predominantly T-cell infiltrate in the alveolar interstitium.
Further evidence of lymphoma can be found by identifying light chain restriction using immunohistochemistry or monoclonality using PCR.
The differential diagnosis of high-grade lymphoma is usually carcinoma.
These are differentiated by using standard epithelial and lymphoid markers.
LIP may also be histologically indistinguishable from extrinsic allergic alveolitis.
In LIP there is absence of an environmental allergen.
There is also some histological and clinical overlap with 'cellular' cases of non-specific interstitial pneumonia.
Therefore, a combination of clinical, radiological and histological information is important for correct classification and appropriate management of the patients.
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