Interstitial Lung Disease

Notes

Overview

Interstitial Lung Disease is also known as Diffuse Parenchymal Lung Disease (DPLD). A Heterogeneous collection of restrictive lung conditions (>100) that primarily (or at least initially) disrupt the pulmonary interstitium. Interstitial Lung Disease (ILD) are grouped together as they share similar pathophysiological mechanisms, clinical features and radiological findings.

Side note

Pulmonary Interstitium: Intervening structural tissue between the alveoli space and pulmonary capillaries. Consists of the basement membrane of endothelial and epithelial cells, collagen fibres, elastic tissue, proteoglycans, fibroblasts, mast cells and mononuclear cells.

Definition

Interstitial Lung Disease: Includes a diverse group of respiratory conditions characterised by inflammation and fibrosis of the interstitium. Worsening hypoxia and respiratory failure may develop with disease progression. The disease is considered a restrictive lung disease
Restrictive Lung Disease: Unable to fully fill the lungs with air. Their lungs are restricted from fully expanding.
Chronic Obstructive Lung Disease: A serious, progressive and disabling condition that limits airflow in the lungs. It includes emphysema and chronic bronchitis. Strongly associated with smoking
Pneumonia: Infection and Inflammation of the Lung paranchyma

Respiratory Anatomy and Physiology

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Respiratory System Overview

Simplified Anatomy of the alveolus and pulmonary capillary. Below is a diagram of the Interstitial Lung Parenchyma from a cross section. Many cells are found here:

Type I Pneumocytes
Type II Pneumocytes which produce surfactant
Alveolar macrophages for pulmonary defences
Interstitial fibroblasts, that make up the ECM and produce collagen and other matrix

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Mechanism of Respiration

Aetiology and Risk Factors

Risk Factors

Age: There is significant variation in the age of onset between different ILDs.

Young adult, Middle-aged – Sarcoidosis, Pulmonary Lagnerhan cells histocytosis
Elderly – Idiopathic pulmonary fibrosis

Gender: There is significant variation in the gender distribution of different ILDs.

Women
- Lymphangioleiomyomatosis
- Lymphocytic interstitial pneumonitis
- Hermansky-Pudlak syndrome
Men
- Rheumatoid Arthritis
- Pneumoconiosis

Pathology

General changes seen in interstitial lung disease. There is proliferation of interstitial fibroblasts and recruitment of fibrocytes into the interstitium (Extracellular matrix [ECM]). These cells begin secreting ECM such as collagen and other fibers. The cells also convert and activate becoming myofibroblasts which further produces ECM. Prolonged fibroblast activity leads to fibrosis a hallmark of interstitial lung disease and restrictive lung pattern.

Clinical Manifestation

Clinical Presentation

Dyspnoea
- Spontaneous pneumothorax – a characteristic finding of certain ILDs (e.g. pulmonary Langerhans cell histiocytosis)
Dry Cough
Haemoptysis – Diffuse alveolar haemorrhage
Wheeze (uncommon)
Chest Pain (uncommon but perhaps in sarcoidosis)
Extrapulmonary Manifestations: May be suggestive of connective tissue disease.

Onset of Symptoms: The duration of symptoms prior to presentation differs between ILDs and therefore may assist in narrowing down the diagnosis.
Acute (days to weeks)	Acute eosinophilic pneumonia, Hypersensitivity pneumonitis
Subacute (weeks to months)	Sarcoidosis
Chronic (Months to years)	Idiopathic pulmonary fibrosis, pulmonary Langerhans cell histiocytosis

Examination

Dyspnoea
Clubbing
Crakles (rales)
Wheeze
Pulmonary hypertension (severe)
Systemic findings
- Skin Changes
- Eye Changes
- Salivary Gland enlargement
- Peripheral Lymphadenopathy
- Hepatosplenomeagly
- Pericarditis
- Myositis

Diagnosis

Viral Pneumonia
Tuberculosis
Fungal infection
Leukaemia
Lymphoma
Pulmonary Oedema
Aspiration Pneumonitis

Investigations

FBC
ABG
LFT
EUC
ANA – if SLE suspected
C-ANCA – if suspect hypersensitivity pneumonitis
Chest X-ray – usually normal
- Small lung volume
- Reticularnodular shadowing
- Hilar / mediastinal lymphanenopathy
CT
- Reticularnodular shadowing
- Ground glass changes
- Honeycomb cysts

Remember

CT changes found in ILD include reticularnodular shadowing, ground glass changes and honeycomb cysts.

Spirometry – Restrictive Pattern
ECG – Pulmonary Hypertension?
- Right axis deviation
- R wave/S wave ratio greater than one in lead V1
- Incomplete or complete right bundle branch block, or increased P wave amplitude in lead II due to right atrial enlargement
Lung Biopsy – Transbronchial or Surgical Lung Biopsy

Remember

ECG Should be performed in all suspected cases of ILD to look for evidence of pulmonary hypertension.

Classification

Due to the extensive number of subtypes, correct diagnosis of ILDs/DPLDs is challenging but essential to ensure optimal treatment and prognosis. Classification is informed by the patients history of exposure, clinical features, serology, radiological pattern and lung biopsy

The major subgroups of ILD are broadly defined as:

Diffuse Parenchymal Lung Disease of known cause
- Drug induced
- Connective tissue disease associated (i.e Rheumatoid arthritis)
Idiopathic interstitial pneumonia
- Idiopathic Pulmonary Fibrosis
- Acute interstitial pneumonia
- Lymphocytic interstitial pneumonia
Granulomatous Diffuse Parenchymal Lung Disease
- Sarcoidosis
- Hypersensitivity pneumonitis
Other Diffuse Parenchymal Lung Disease
- Pulmonary Lagnerhan cells histocytosis

Sarcoidosis is a multi-system disease that results in pulmonary fibrosis in up to 20% of patients. Aetiology is unknown. However, well-formed granulomas, the characteristic pathological lesion, are thought to form in response to a variety of environmental stimuli (eg infection, inorganic particles and certain chemicals).

Connective tissue disease associated ILD This includes scleroderma, systemic lupus erythematosus, rheumatoid arthritis, dermatopolymyositis and mixed connective tissue disease. Immune-mediated inflammation of the lung interstitium can occur, sometimes progressing to irreversible fibrosis if it is left untreated.

Complications

Common Comorbidities in Interstitial Lung Disease

GORD/GERD

Osteoporosis

Infections

Obstructive sleep apnea

Pulmonary hypertension

Restrictive vs. Obstructive

Remember

The hallmark of restrictive lung disease is decreased lung capacities, particularly the TLC but also the vital capacity.

Remember

In both obstructive and restrictive lung disease, the FEV1 is decreased, the FEV1 /FVC is decreased in obstructive processes and normal in restrictive processes.