Interstitial lung disease

Interstitial lung disease (ILD) encompasses numerous lung conditions that may be non-infectious and non-malignant and involve the interstitium of the lung. It may also be referred to as diffuse parenchyma lung disease (DPLD).

🦴 Anatomy

The lung interstitium is a collection of supportive tissue including alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues.

There are 3 anatomical zones:

1. Axial interstitium - within the bronchial spaces.
2. Parenchymal interstitium - intralobular spaces.
3. Peripheral interstitium - Inter lobular spaces and pleural cavity.

The management of ILDs is usually to manage the underlying cause, immunomodulation, cyclophosphamide, palliative care.

🔢 Classification

There is no universal method of classifying ILDs, however, we can categorise them as such:

We will be focusing on idiopathic pulmonary fibrosis in this CCC. Environmental ILDs will be discussed in occupational lung disease.

PULMONARY FIBROSIS/IDIOPATHIC PULMONARY FIBROSIS

🫁 Pulmonary fibrosis

Pulmonary fibrosis refers to the chronic, lifelong alteration of the lung in which there is fibrotic scar tissue formation. No matter what the cause is, there is a pro-inflammatory response and pro-fibrotic response by activation of macrophages and fibroblasts.

Pulmonary fibrosis is a restrictive lung disease.

Some of the causes of pulmonary fibrosis include:

• Lung damage - infarction, pneumonia, TB.
• Irritants - coal dust, silica.
• Idiopathic
• Connective tissue diseases - RA, SLE, systemic sclerosis, Sjögren’s syndrome.
• Medication - amiodarone, nitrofurantoin, bleomycin, busulfan methotrexate.
• Hypersensitivity pneumonitis - exposure to birds or moulds.

🫁 Idiopathic pulmonary fibrosis

IPF is rare and life-threatening manifesting over several years characterised by the formation of fibrotic scar tissue within the lungs. It leads to progressive dyspnoea. It is synonymous with cryptosing fibrosing alveolitis (CFA).

IPF has no underlying cause.

🏘️ Epidemiology

It is the most common interstitial lung disease.

Males are 2x likely to get pulmonary fibrosis.

The median age of presentation is 70 years old.

The prognosis is very poor with a life-expectancy of 3-4 years after diagnosis. However, the progression of the disease is variable and some patients remain subclinical their entire life.

😷 Presentation

🔍 Investigations

📷

Imaging:

• 🏆 High resolution CT - gold-standard investigation to establish diagnosis. It will show reticulo-nodular shadowing or ground glass opacities which can progress to honeycomb lung.
• Ground glass opacities are an area of increased opacities through which we may still see vessels and bronchial structures.
• Honeycomb lung - clustered cystic air spaces. There are multiple lucent shadows ranging from 2-10mm in size.

The transition from ground glass to honeycombing is seen in pulmonary fibrosis as the inflammation progresses to fibrosis.

• CXR - bilateral lower zone reticulo-nodular shadowing. Also shows ground glass opacities which can progress to honeycombing later on.

Other tests that may be done include:

• Bloods
• CRP
• ANA - positive in 30% of patients.
• Rheumatoid factor (RF) - positive in 10% of patients.
• ABG - may indicate hypoxia and hypercapnia.
• Spirometry - will show a restrictive pattern (normal or decreased FEV1, decreased FVC, increased FEV1/FVC ratio.

🧰 Management

IPF is irreversible so the focus is primarily on conservative management and palliative care:

The definitive management is lung transplantation.

🚨 Complications