Interstitial Lung Disease: a guide to understanding the term and navigating the diagnosis

When discussing lung conditions, the term ‘interstitial lung disease’ (ILD) often pops up. But what does this term mean? It’s an umbrella term that covers over a hundred different lung conditions. All of them affect the interstitium, the tissue and space surrounding the lungs’ tiny air sacs (alveoli). When this area becomes damaged, it can lead to inflammation and scarring, affecting your ability to breathe and deliver oxygen to the body.

Pulmonary Fibrosis and Interstitial Lung Disease: The Difference

You may often hear pulmonary fibrosis and ILD used interchangeably, but it’s vital to understand the difference. Pulmonary fibrosis is a type of interstitial lung disease characterised by the thickening and scarring (fibrosis) of the lung tissue. Essentially, all pulmonary fibrosis cases are ILDs, but not all ILDs are pulmonary fibrosis.

Types of Interstitial Lung Disease

As an umbrella term, ILD covers various conditions. Here, we’ll briefly summarise some key types:

1. Idiopathic Pulmonary Fibrosis (IPF): This is a chronic condition where the lungs become scarred, causing breathing difficulties. While it is serious, and has a poor prognosis with a life expectancy of 3-5 years post-diagnosis, treatment can manage symptoms and slow disease progression.
2. Non-Specific Interstitial Pneumonia (NSIP): This condition features widespread inflammation and scarring in the lung tissue, but generally has a more favourable prognosis than IPF. Symptoms can be managed with steroids and other immunosuppressive therapies.
3. Cryptogenic Organizing Pneumonia (COP): Previously known as bronchiolitis obliterans organising pneumonia, COP is characterised by inflammation and scarring primarily affecting the small airways (bronchioles) and surrounding lung tissue. It generally responds well to corticosteroid treatment.
4. Acute Interstitial Pneumonia (AIP): Also known as Hamman-Rich syndrome, this is a severe and rapidly progressive form of ILD. It presents suddenly with severe breathing difficulties and often requires intensive care.
5. Desquamative Interstitial Pneumonia (DIP): Mostly found in current or former smokers, DIP is characterised by the accumulation of immune cells within the air sacs, causing inflammation. It generally responds well to corticosteroid therapy, and prognosis is often better with smoking cessation.
6. Respiratory Bronchiolitis-Interstitial Lung Disease (RB-ILD): Also associated with smoking, RB-ILD causes inflammation and mild scarring in the small airways and surrounding lung tissue. Most patients with RB-ILD are asymptomatic or mildly symptomatic, and prognosis is good.
7. Lymphocytic Interstitial Pneumonia (LIP): A rare form of ILD causing infiltration of lymphocytes into lung tissue. Often associated with autoimmune diseases or certain infections, its course is highly variable but tends to be slowly progressive.
8. Sarcoidosis: This disease is characterised by the formation of small inflammatory nodules (granulomas) in the lungs or other organs. It often resolves spontaneously, though in some cases, long-term treatment may be needed.
9. Asbestosis: Caused by inhalation of asbestos fibres, this disease leads to lung scarring and breathing difficulties. Prognosis is variable, depending on the extent of exposure and disease progression.
10. Silicosis: An occupational lung disease caused by inhalation of silica dust, leading to lung scarring. Chronic silicosis progresses slowly over many years, while acute silicosis can progress rapidly.
11. Hypersensitivity Pneumonitis (HP): Resulting from an allergic reaction to inhaled substances, HP causes lung inflammation and, if not avoided, the offending substance can cause permanent lung damage. Prognosis varies depending on the stage at diagnosis.
12. Eosinophilic Pneumonia: A rare condition where a type of white blood cell, eosinophils, accumulates in the lungs, causing inflammation. It usually responds well to corticosteroids, and the prognosis is generally good with treatment.
13. Rheumatoid Lung Disease: This occurs when rheumatoid arthritis affects the lungs, leading to various forms of ILD. The course and prognosis vary widely, depending on the specific subtype and severity.
14. Systemic Sclerosis-related ILD: In systemic sclerosis, or scleroderma, fibrosis can affect the lung tissue, causing shortness of breath and decreased lung function. Prognosis depends on the severity of the lung involvement.
15. Pleuroparenchymal Fibroelastosis (PPFE): A rare condition causing fibrosis and thickening of the upper lobes and the lining around the lungs. Prognosis varies, with some cases progressing to respiratory failure.
16. Pulmonary Langerhans Cell Histiocytosis (PLCH): A rare disease where specific white blood cells form nodules in the lungs. It’s often related to smoking. Prognosis is variable, and many patients stabilize or improve with smoking cessation.
17. Drug-induced Interstitial Lung Disease: Certain medications can cause an adverse reaction leading to lung tissue inflammation. Prognosis is generally favourable if the offending drug is identified and discontinued.
18. Radiation-induced Lung Disease: A possible side effect of radiation therapy for lung or breast cancer, it can cause inflammation and fibrosis in the irradiated area. Management strategies can limit progression, improving prognosis.
19. Lymphangioleiomyomatosis (LAM): A rare lung disease, mostly affecting women, where muscle cells proliferate in the lungs, leading to cyst formation and lung dysfunction. It tends to progress slowly, and prognosis varies widely.
20. Occupational Lung Diseases: A group of lung diseases caused by inhaling certain harmful substances in the workplace. Besides asbestosis and silicosis, which we’ve already mentioned, other examples include coal worker’s pneumoconiosis (black lung disease) and hard metal pneumoconiosis. Symptoms, progression, and prognosis vary greatly depending on the specific substance involved, duration of exposure, and individual susceptibility.

Symptoms of Interstitial Lung Disease

One of the more challenging aspects of ILD is that symptoms can vary greatly from person to person, depending on the type of ILD. However, some common symptoms include:

1. Shortness of Breath: This is often the most noticeable symptom. At first, it may only occur during physical activity, but as the disease progresses, it can happen even at rest.
2. Persistent Dry Cough: A non-productive (not bringing up mucus) cough that doesn’t go away can be a common symptom of ILD.
3. Fatigue: Patients may feel unusually tired or lack energy, even after a good night’s sleep.
4. Unintended Weight Loss: Some individuals with ILD may notice a decrease in appetite and an unexplained weight loss.
5. Discomfort in the Chest: Patients may experience a sense of pressure or pain in the chest, particularly when taking deep breaths.
6. Clubbing of Fingers or Toes: The tips of the fingers or toes may widen and become rounder than normal. The nails may also curve around the fingertips. This symptom usually indicates more advanced or severe disease.
7. General Malaise: Patients may feel generally unwell, with a decreased ability to perform regular activities.

Diagnosing Interstitial Lung Disease

The diagnosis of ILD involves several steps. Initially, your respiratory specialist will take a detailed history and perform a physical examination. You may be asked about your occupational and environmental exposures, any history of smoking, or family history of lung disease.

Imaging studies, like a high-resolution CT scan, provide detailed pictures of your lungs. This imaging is one of the most vital tools in diagnosing ILD, helping doctors differentiate between various types.

In some cases, a procedure called bronchoscopy and bronchoalveolar lavage may be recommended. This involves inserting a thin tube into the lungs to collect cells for microscopic examination.

Your respiratory specialist will also suggest a pulmonary function test, which measures how well your lungs work, and a blood test to check for conditions associated with ILD, and to monitor progression of the disease and response to treatment.

Complications of Interstitial Lung Disease

If left unchecked, ILD can lead to severe complications. These include pulmonary hypertension, which is high blood pressure in the arteries supplying the lungs, and respiratory failure, which may require oxygen therapy or even a lung transplant.

In severe cases, ILD can also lead to heart failure due to the increased strain on the heart, and a decreased ability to exercise or perform daily activities.

Prognosis of Interstitial Lung Disease

The prognosis for ILD varies greatly depending on the specific type of disease, its severity, and the individual’s overall health. Some ILDs progress slowly over several years, while others can worsen rapidly. Early detection and appropriate treatment can often slow disease progression and improve quality of life.

Management and Treatment of Interstitial Lung Disease

Management and treatment of ILD depend on the specific type and severity of the disease. This can range from medication (such as corticosteroids, immunosuppressants, or newer anti-fibrotic drugs) to lung rehabilitation programs and, in severe cases, lung transplantation.

Lifestyle modifications like quitting smoking, avoiding lung irritants, getting regular vaccinations, and maintaining a healthy diet and exercise regime can also help manage the disease.