Etymology

• Derived from the Latin word folliculus, meaning “little sac,” and the Greek words bronchion, meaning “small airway,” and -itis, meaning “inflammation.” The term refers to inflammation of the bronchioles characterized by lymphoid follicle formation.

AKA

• Lymphoid follicular bronchiolitis

What is it?

• Follicular bronchiolitis is a rare inflammatory condition of the small airways characterized by the presence of hyperplastic lymphoid follicles within and around the bronchioles. It is often associated with underlying autoimmune or connective tissue diseases.

Caused by:

• Most common causes:
  • Connective tissue diseases (e.g., rheumatoid arthritis, Sjögren’s syndrome)
  • Immune deficiency disorders (e.g., common variable immunodeficiency)
• Less common causes:
  • Infection:
    • Chronic or recurrent respiratory infections
  • Inflammation:
    • Hypersensitivity reactions
  • Immune:
    • Autoimmune disorders (e.g., systemic lupus erythematosus)
  • Inherited and Congenital:
    • Genetic conditions predisposing to immune dysregulation
  • Other:
    • Idiopathic follicular bronchiolitis

Resulting in:

• Narrowing and obstruction of small airways
• Chronic inflammation and mucus stasis
• Impaired gas exchange

Structural Changes:

• Hyperplastic lymphoid follicles around bronchioles
• Bronchiolar wall thickening
• Peribronchiolar inflammation and fibrosis in chronic cases

Pathophysiology:

• Follicular bronchiolitis arises from chronic immune activation, often triggered by infection, autoimmunity, or immune deficiency. Lymphoid follicles proliferate in response to antigenic stimulation, causing bronchiolar narrowing and airflow obstruction. Persistent inflammation can lead to secondary fibrosis and remodeling of small airways.

Pathology:

• Enlarged lymphoid follicles with germinal centers around bronchioles
• Chronic inflammatory infiltrates in the bronchiolar walls
• Associated fibrosis in advanced stages

Diagnosis

Clinical:

• Symptoms include:
  • Chronic cough
  • Progressive dyspnea
  • Wheezing in some cases
  • Recurrent respiratory infections
• History of underlying autoimmune or immune deficiency disorder

Radiology:

• CXR:
  • Non-specific findings such as reticulonodular opacities
  • Peribronchial thickening in some cases
• CT of the Chest:
  • Centrilobular nodules
  • Ground-glass opacities
  • Mosaic attenuation indicating air trapping
  • Bronchiolar wall thickening

Labs:

• Autoimmune panel to detect associated connective tissue diseases
• Serum immunoglobulin levels for immune deficiencies
• Microbiological cultures to rule out infections

Management:

• Treatment of underlying conditions:
  • Immunosuppressive therapy (e.g., corticosteroids, disease-modifying agents) for autoimmune diseases
  • Immunoglobulin replacement for immune deficiencies
• Supportive care:
  • Bronchodilators for symptomatic relief
  • Management of superimposed infections

Radiology Detail

CXR

Findings:

• Reticulonodular or peribronchial opacities

Associated Findings:

• Hyperinflation in cases with air trapping

CT of the Chest

Parts:

• Terminal and respiratory bronchioles

Size:

• Centrilobular nodules typically 2-3 mm in diameter

Shape:

• Small, rounded nodules or irregular thickening

Position:

• Centrilobular distribution in the lung parenchyma

Character:

• Nodular opacities with ground-glass attenuation

Time:

• Chronic process, often progressive

Associated Findings:

• Air trapping on expiratory imaging
• Peribronchial thickening

Other relevant Imaging Modalities

MRI/PET CT/NM/US/Angio:

• PET-CT: May demonstrate metabolic activity in areas of inflammation or lymphoid hyperplasia

Pulmonary Function Tests (PFTs):

• Restrictive or obstructive patterns depending on the stage of the disease
• Reduced diffusion capacity in advanced cases

Recommendations:

• High-resolution CT for detailed assessment of small airway involvement
• Biopsy for definitive diagnosis if imaging and clinical correlation are inconclusive
• Early identification and management of underlying autoimmune or immune deficiency disorders

Key Points and Pearls:

• Follicular bronchiolitis is a rare condition associated with autoimmune diseases and immune deficiencies.
• High-resolution CT findings include centrilobular nodules and air trapping.
• Management focuses on treating underlying conditions and providing supportive care.
• Biopsy may be required for a definitive diagnosis in uncertain cases.

 

Follicular Bronchiolitis  Associated with Rheumatoid Arthritis

Follicular Bronchiolitis,, Centrilobular Nodules, Air Trapping, Ground Glass Opacities (GGO) in Upper Lobes

• 

  • aka bronchiolar nodular lymphoid hyperplasia,
  • aka hyperplasia of the bronchial associated lymphoid tissue (BALT),
  • is a
    • reactive pulmonary lymphoid disorders
    • part of as group of
      • lymphoproliferative pulmonary diseases (LPDs).
  • characterized by the
  • accumulation of lymphoid cells in the
  • walls of small airways.
  •  caused by
    • antigenic stimulation of BALT, followed by a
    • polyclonal lymphoid hyperplasia. It is currently classified as one of the reactive pulmonary lymphoid disorders in a group known as the lymphoproliferative pulmonary diseases (LPDs).
    • primary
    • secondary
      • Connective Tissue Disorders
        • Sjogren’s syndrome,
        • rheumatoid arthritis, and
        • systemic lupus erythematosus
      • Infection
        • Pneumocystis jirovecii,
        • Legionella pneumonia, and
        • acute viral hepatitis
      • ILD
        • lymphoid interstitial pneumonia,
        • respiratory bronchiolitis-associated interstitial lung disease,
        • desquamative interstitial pneumonia,
        • cryptogenic organizing pneumonia, and
      • Immunodeficiencies
        • CVID and AIDS