• LIP is a rare interstitial lung disease characterized by the diffuse proliferation of lymphoid tissue within the lung interstitium.
• In lymphocytic interstitial pneumonia (LIP), there is an inflammatory component as well as infiltrative features.

• Etymology

  • Derived from “lymphocytic,” referring to lymphocytes, and “interstitial pneumonia,” indicating inflammation primarily affecting the lung interstitium.

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  AKA and abbreviation

  • Lymphocytic interstitial pneumonia (LIP).
• What is it:
• LIP is a rare, benign lymphoproliferative disorder characterized by diffuse lymphocytic infiltration of the pulmonary interstitium, alveolar septa, and associated lymphatic structures.
  •  is a rare form of interstitial lung disease (ILD) characterized by:
    • Diffuse or patchy lymphocytic infiltration of the
      • airways
      • interstitium and
      • alveolar walls
    • Associated with
      • It often occurs in association with autoimmune diseases, immunodeficiency syndromes, or chronic antigenic stimulation.
      • hyperplasia of lymphoid tissue in the lungs.
  • LIP can occur as an
    • idiopathic condition or
    • secondary to other systemic diseases.

• Characterized by

  • Histological findings:
    • Dense interstitial infiltration of mature lymphocytes, plasma cells, and histiocytes.
    • Prominent lymphoid aggregates with or without germinal centers in the interstitium.
    • Sparing of the airways in most cases.
  • Imaging features:
    • Diffuse or patchy ground-glass opacities.
    • Perilymphatic or randomly distributed thin-walled cysts.
    • Reticulonodular opacities and septal thickening.
    • Upper and lower lobe involvement with subpleural predominance.
  • Associated findings:
    • Mediastinal or hilar lymphadenopathy.
    • Pleural effusions (rare).

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  Anatomical Context

  • Primarily affects the pulmonary interstitium, including:
    • Alveolar walls.
    • Peribronchovascular lymphatic structures.
    • Subpleural and interlobular septal regions.

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  Caused by

  Most common cause: Autoimmune diseases.

  Other causes include:

  • Autoimmune diseases:
    • Sjögren syndrome (most common).
    • Systemic lupus erythematosus (SLE).
    • Rheumatoid arthritis.
  • Immunodeficiency syndromes:
    • Common variable immunodeficiency (CVID).
    • HIV/AIDS (especially in children).
  • Virus-associated:
    • Epstein–Barr virus (EBV).
    • Human immunodeficiency virus (HIV).
  • Other:
    • Idiopathic cases.
    • Post-transplant immune reconstitution.

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  Resulting in

  • Chronic lymphocytic infiltration of the interstitium.
  • Diffuse pulmonary inflammation, potential fibrosis, and cystic changes.
  • Impaired gas exchange and restrictive lung physiology.

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  Structural changes

  • Inflammation: Diffuse lymphocytic infiltration in the interstitial tissue.
  • Cysts: Thin-walled cysts due to peribronchial lymphoid tissue hyperplasia and alveolar destruction.
  • Fibrosis: In advanced cases, interstitial fibrosis may develop.

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  Pathophysiology

  • Chronic antigenic stimulation triggers lymphocytic proliferation within the pulmonary interstitium.
  • Progressive inflammation leads to diffuse interstitial involvement and the formation of lymphoid follicles.
  • Cystic changes occur due to obstruction of bronchioles by peribronchial lymphoid aggregates.

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  Pathology

  • Interstitial expansion by lymphocytic infiltrates, predominantly CD4+ and CD8+ T cells.
  • Follicular hyperplasia with germinal centers.
  • Minimal to no granulomatous inflammation.

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  Diagnosis

  • Clinical correlation: Symptoms such as cough, dyspnea, and systemic features like fever or weight loss.
  • Imaging:
    • HRCT: Diffuse ground-glass opacities, reticulonodular patterns, and cysts.
    • CXR: Reticulonodular opacities; less specific than CT.
  • Biopsy: Definitive diagnosis requires histopathological confirmation.

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  Clinical

  • Symptoms:
    • Insidious onset of dyspnea and non-productive cough.
    • Systemic symptoms: Fatigue, weight loss, low-grade fever.
  • Signs:
    • Inspiratory crackles (in advanced cases).
    • Extrapulmonary manifestations of associated autoimmune diseases (e.g., xerostomia in Sjögren syndrome).

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  Radiology Detail

  CXR:

  • Findings: Reticulonodular opacities with lower lobe predominance.

  CT:

  • Parts: Alveolar walls, peribronchovascular interstitium, and subpleural regions.
  • Size: Cysts typically measure 1-3 cm.
  • Shape: Round, thin-walled cysts; diffuse ground-glass opacities and reticular changes.
  • Position: Predominantly basal and subpleural distribution.
  • Character:
    • Mixed reticular and ground-glass patterns.
    • Associated nodules and cysts.

  Other relevant Imaging Modalities:

  • MRI: Limited utility for LIP.
  • PET-CT: May show mild metabolic activity in lymphoid aggregates.

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  Pulmonary function tests (PFTs)

  • Restrictive pattern with reduced lung volumes (e.g., FVC, TLC).
  • Impaired diffusion capacity (DLCO).

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  Recommendations

  • Imaging follow-up: Periodic HRCT to monitor disease progression or response to treatment.
  • Biopsy: Required for definitive diagnosis in ambiguous cases.
  • Treatment:
    • Treat underlying autoimmune or immunodeficiency conditions.
    • Corticosteroids or immunosuppressants for progressive disease.
    • Antiretroviral therapy in HIV-associated LIP.

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  Key Points and Pearls

  • LIP is strongly associated with autoimmune diseases (e.g., Sjögren syndrome) and immunodeficiency syndromes (e.g., CVID).
  • Characteristic imaging findings include diffuse ground-glass opacities, cysts, and reticulonodular patterns.
  • Diagnosis requires integration of clinical, radiologic, and histopathologic findings.
  • Untreated, LIP may progress to interstitial fibrosis or transform into lymphoma, particularly in the setting of immunodeficiency.
• 

Inflammatory Component in the
Interalveolar Septa

Infiltrative Component of
Lymphocytes Plasma Cell And Histiocytes

Key Pathological Features

1. Inflammatory Component:
   • LIP is primarily driven by a polyclonal lymphocytic infiltration of the interstitium.
   • This inflammation predominantly consists of T-cells, with smaller numbers of B-cells and plasma cells.
   • The inflammation may also extend to involve alveolar walls, airways, and blood vessels.
2. Infiltrative Features:
   • Reactive lymphoid hyperplasia is a hallmark, with scattered lymphoid aggregates sometimes forming germinal centers.
   • These lymphoid infiltrates can involve peribronchovascular areas, interlobular septa, and subpleural regions.
3. Associated Findings:
   • Occasionally, there is infiltration of plasma cells that may produce immunoglobulin, potentially leading to the presence of monoclonal protein production in rare cases (e.g., in the context of Sjögren’s syndrome).
   • The alveolar spaces may show collections of macrophages and lymphocytes.

Imaging Correlation

On HRCT, LIP typically shows:

• Diffuse or patchy ground-glass opacities (inflammatory component).
• Thin-walled cysts scattered in a random distribution.
• Reticular or nodular opacities, particularly in the peribronchovascular or lower lung zones.
• In severe or chronic cases, fibrosis may develop.

Clinical Significance

The inflammatory nature of LIP is critical because it means the disease can respond to immunosuppressive therapy (e.g., corticosteroids or other immunomodulatory agents). However, progression to fibrosis or transformation into lymphoid malignancy (e.g., lymphoma) is a potential concern.

In summary, LIP includes both an inflammatory and an infiltrative component, with the inflammatory aspect being central to its pathogenesis and clinical management.

• Lower and midlung predominance
• infiltration of lymphocytes and plasma cells into the
  • perilymphatic
    • bronchovascular bundles
    • venules
  • interstitium.

Lymphocytic Infiltration  Along the
Bronchovascular Bundles in the Mid and
Lower Lung Fields

Lymphocytic Infiltration  Along the
Lymphatics of the
Interalveolar and
Interlobular Septa

Infiltration of Lymphocytes, Plasma Cells, and Histiocytes into the
Walls of the Bronchioles and Small Airways, Obstruction,
Necrosis and
Cyst Formation

 Mid and Lower Lung Field
Thin Walled Cysts

Thin Walled Cysts in
Close Association with Bronchovascular Bundles

Nodules
Ill Defined Centrilobular and Subpleural Nodules

 

CT Finding	Description
Cysts and Nodules:	Development of cysts and nodules varying in size and distribution. hypotheses perhaps bronchiolar obstruction similar to the pathogenesis of Langerhans cysts but many other hypotheses
Peribronchovascular and Perilymphatic Distribution:	Clustering of lymphocytic infiltrates around bronchovascular bundles and lymphatic vessels.
Interstitial Thickening:	Thickening of interlobular septa and bronchovascular bundles contributing to a reticular pattern.
Ground-Glass Centrilobular Nodules:	Centrilobular ground-glass nodules may be present.

CT Finding	Description
Ground-Glass Opacities (GGOs):	Bilateral and diffuse opacities indicating partial airspace filling.
Interstitial Thickening:	Thickening of interlobular septa and bronchovascular bundles contributing to a reticular pattern.
Cysts and Nodules:	Development of cysts and nodules varying in size and distribution.
Ground-Glass Centrilobular Nodules:	Centrilobular ground-glass nodules may be present.
Pleural Effusion:	Pleural effusion is not common but mild effusion may be observed in some cases.

Rare

• Typical onset at ages 40 – 70 years old but can occur at any age (Chest 2002;122:2150)
• Typically in patients with Sjogren’s syndrome
• lower lobe predominance
• GGO’s
• Can have MALT lymphoma
• and Amyloidosis Light chain deposition disease
• More common in women
• No association with smoking history

• Bilateral lower lobes of the lung but also mid lung zones

Lower Lobes predominant Why?

• exact reason for this preference is
• not completely understood,
  • One possible explanation
  • lower lobes of the lungs are
  • more dependent on gravity, which
  • may affect the distribution of
  • lymphocytes and
  • other immune cells that are involved in the development of LIP.
    • Gravity may cause these cells to accumulate more easily in the lower lobes, where
    • blood flow and ventilation are also generally
      • lower
      • compared to the upper lobes.
• lymphatic drainage of the lower lobes
• less than the upper lobes, which could lead to the
  • accumulation of lymphocytes in the lower lobes.
• certain infections or environmental exposures that may
• contribute to the development of LIP
• may also have a greater impact on the lower lobes of the lungs.

Disease Process

• infiltration of lymphocytes and plasma cells into the lung interstitium

 

 

• Pathogenic mechanisms of LIP are still unclear
• Has aspects of lymphoproliferative disease and lymphoid hyperplasia of polyclonal T or B cells (Chest 2002;122:2150)
• Although it may transform to lymphoma, especially MALT, the risk is lower than initially reported (Eur Respir J 2006;28:364)

• Associated with several systemic diseases and conditions
  • Autoimmune (most common)
    • Sjögren syndrome (SjS); 25% of LIP cases have SjS and 1% of SjS cases present with LIP
    • Rheumatoid arthritis
    • Systemic lupus erythematosus
    • Polymyositis / dermatomyositis
    • Hashimoto disease
    • Hypothyroidism
    • Castleman disease
    • Myasthenia gravis
    • Autoimmune hemolytic anemia
    • Pernicious anemia
    • Primary biliary cirrhosis
  • Infection
    • Human immunodeficiency virus (HIV)
    • Epstein-Barr virus
    • Human T cell lymphotropic virus type 1
    • Legionella pneumonia
    • Mycoplasma
    • Chlamydia
    • Tuberculosis
  • Immunodeficiency
    • Acquired immunodeficiency syndrome (AIDS); especially in children
    • Monoclonal or polyclonal gammopathy
    • Common variable immunodeficiency
  • Idiopathic LIP accounts for 20% of cases (Eur Respir J 2006;28:364)

• Very slowly progressive respiratory symptoms
  • Dyspnea on exertion
  • Dry cough
  • Systemic symptoms such as malaise, fever and weight loss
  • Duration of the symptoms prior to diagnosis can exceed a year
• Bibasilar inspiratory crackles on chest auscultation

• Based on clinical, radiological and pathological findings (multidisciplinary diagnosis)
• No firm diagnostic criteria currently exist

• Dysproteinemia is often present
  • Hypergammaglobulinemia is more common than hypogammaglobulinemia
• Restrictive pattern on pulmonary function tests
  • Reduced forced vital capacity (FVC)
  • Reduced diffusing capacity of the lung for carbon monoxide (DLCO)

• Chest radiography
  • Bibasilar opacities with lower lobe predominance
• High resolution computed tomography (Eur J Radiol 2015;84:542, Respirology 2016;21:600)
  • Ground glass opacity with / without consolidation with lower lobe predominance
  • Cyst formation and thickening of bronchovascular bundle and interlobular septa are often present
  • Cysts often remain even after resolution of symptoms