Interstitial Lung Disease: An Overview

 

Interstitial Lung Disease (ILD) can be a confusing topic – with a plethora of acronyms used to describe similar conditions –  however, this post attempts to clarify the categories of ILD and provide a brief overview of the topic as a whole. To begin – lets deal with the common clinical features found in idividuals with ILD.

Clinical Features

  • Dry Cough
  • Dyspnoea
  • Auscultation:”Fine Inspiratory Velcro-like Crackles” with or without decreased air entry
  • Restrictive Spirometry results
  • Abnormal CXR/CT
  • History: Specific patient risk factors for ILD

Types of ILD are multiple and can be catagorised according either location or cause

  1. Anatomical Location – Upper or Lower Zones
  2. Cause – Is the cause known or unknown

 

  1. ANATOMICAL LOCATION

When examining ILD in terms of lung zones the majority of pathologies tend to favour either upper or lower zones, giving clues in the clinical setting which can aid diagnosis. As a general rule, aerosolised particles tend towards upper lobe fibrosis and more systemic conditions & toxins tend towards lower lobe fibrosis.

The diagram below shows that conditions such as TB/Pneumoconiosis/Extrinsic Allergic Alveolitis/Aspergillosis tend towards the upper zones – due to the aerosolised nature of their particles. Lower zone predominant conditions include primary and secondary fibrosing conditions (explained below), Rheumatological conditions (Ulcerative Colitis/R.A/SLE).

*The two exceptions to the rule are Ankylosing Spondylitis and Asbestosis – which trade places respectively. ACEPT = upper lobe. downSTAIRs = lower lobe.

ILD2


 

2. Causes of Interstitial Lung Disease

The specific type of interstitial lung diseases are easier to organise in terms of whether or not the cause is known. While not exhaustive, the following flowchart provides a basic breakdown of categories and gives structure to mentally organise the various causes.

Of ILD cases with an identifiable cause the following are the catagories from left to right in the below image

  1. Drugs – Bleomycin, Busulfan, Amiodarone, MTX, 5-ASA, Nitrofurantoin (note that both Rheumatological conditions and their common treatments – MTX/5-ASA can cause fibrosis) Mx: Stop offending drug
  2. Pneumoconiosis – Coal/Silica/Farmers lung Mx: Avoid Exposure
  3. Rheumatological Conditions – RA/ SLE/UC/Sjogrens/Systemic Sclerosis Mx: Manage rheumatological condition
  4. Infective Conditions – Tuberculosis Mx: Treat infection
  5. Carcinoma – Ca Lung/Lymphoma Mx: Treat carcinoma

 

Interstitial Lung Disease
Conceptual breakdown of Interstitial Lung Disease (Mx=Management)

Catagories of Interstital Lung Disease

Of ILD cases without an identifiable cause – the term Idiopathic Interstitial Pneumonia (IIP) is used as an encompassing umbrella term. Idiopathic pulmonary fibrosis is the most common of IIP’s.

Idiopathic pulmonary fibrosis (IPF) is a progressive primary fibrosing disease. The term may be thought of as somewhat interchangeable with usual interstitial pneumonia (UIP) – its histological description. IPF is furthermore described as a primary fibrosis condition, in comparison to others, which are described as secondary fibrosing conditions. As IPF is a primary fibrosing condition – an anti-fibrotic medication is the main stay of treatment. Pirfenidone, which works via the inhibition of TGF-β has good clinical efficacy in IPF.

 

General Interstitial Lung Disease Workup

  • Hx and examination – focusing on the above causes/duration/zone predominance
  • CXR
  • High Resolution CT
  • Sputum Sample & Quantiferon/AFB
  • Bronchoscopy with biopsy/bronchoalveolar lavage

 

Summary

  1. Interstitial lung disease can be categorized into whether or not a cause is readily identifiable in the clinical history/histology.
  2. Commonly identifiable causes include drugs, toxins, rheumatological conditions, carcinomas and pneumoconioses. Avoidance/Treatment of the specific cause is the mainstay of treatment.
  3. Pulmonary fibrosis without a causes is most commonly found to be IPF – the main treatment of which is the anti-fibrotic agent Pirfenidone.
  4. The mainstay of therapy for the other IIP’s is typically steroids or lung transplantation.
  5. Upper or lower zone fibrosis may aid clinically in the diagnosis of specific types of Pulmonary fibrosis.
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