Follicular bronchiolitis

Follicular bronchiolitis (FB) is a non-neoplastic primary polyclonal B cell hyperplasia of the bronchus-associated lymphoid tissue (BALT) due to chronic exposure to antigens in those with underlying collagen vascular or immune deficiency diseases which usually manifested as small centrilobular ground glass nodules with lower lobe distribution. 

Epidemiology

Associations

Many cases of follicular bronchiolitis are associated with various systemic illnesses which include

• collagen vascular disease / connective tissue diseases ^1,2

  • Sjögren syndrome - see Sjögren syndrome (thoracic manifestations)

  • rheumatoid arthritis ⁵ - see pulmonary manifestations of rheumatoid arthritis

• immunodeficiency states, both congenital and acquired:

  • AIDS: HIV associated follicular bronchiolitis

• idiopathic

Pathology

It is defined as lymphoid hyperplasia of the BALT and histologically characterized by polyclonal B cell hyperplasia of the lymphoid follicles with reactive germinal centers principally distributed along bronchioles with only minimal infiltration of alveolar septa.

Radiographic features

CT chest

A key feature described with follicular bronchiolitis on HRCT includes small ground glass centrilobular nodules of 3 mm diameter in lower lobes that are variably associated with peribronchial nodules ¹.

Other features, albeit non-specific, include:

• tree in bud changes ²

• parenchymal cysts ²

Treatment and prognosis

Treatment should target the underlying condition, as well as administration of steroids and immunosuppressants. The overall prognosis depends on the underlying or associated abnormality. Some cases may respond to macrolide antibiotics ⁶.

Differential diagnosis

• hypersensitivity pneumonitis: history of environmental/organic antigen exposure

• respiratory bronchiolitis: history of smoking

• infection