Interstitial Lung Disease and Pulmonary Fibrosis

What is interstitial lung disease?

Interstitial lung disease is an umbrella term for more than two hundred conditions that inflame or scar the interstitium, the thin supporting tissue that surrounds the air sacs and carries the capillaries where oxygen enters the blood. When this tissue thickens, oxygen crosses less easily and the lung becomes stiff, so breathing takes more effort and the lungs hold less air. Where scarring dominates, the process is called pulmonary fibrosis.

ILD behaves very differently from asthma or COPD. The problem is not narrowed airways but reduced expansion and impaired gas transfer, which is why patients describe breathlessness on exertion with a dry cough rather than wheeze and sputum. Because early symptoms are subtle, many patients are treated for months as bronchitis, asthma or, in India, as smear-negative tuberculosis before the correct diagnosis is reached.

Getting the specific diagnosis right matters enormously, because treatment diverges sharply. Some ILDs improve substantially with immunosuppression, while others are made worse by it and need antifibrotic drugs instead. Identifying and removing an environmental trigger can halt the disease altogether in the right patient.

Symptoms of ILD and pulmonary fibrosis

• Progressive breathlessness on exertion, developing over months rather than days, initially only on stairs or brisk walking.
• Persistent dry cough that does not respond to antibiotics, cough syrups or inhalers.
• Fatigue and reduced exercise tolerance out of proportion to age or fitness.
• Weight loss in some patients, particularly with connective tissue disease.
• Clubbing of the fingertips, a broadening of the nail bed seen in a proportion of fibrotic ILDs.
• Fine crackles at the lung bases on examination, often described as sounding like Velcro being separated.
• Low oxygen levels on exertion, sometimes with normal resting saturation, which is why walk testing is important.

Symptoms outside the chest can be the key to the diagnosis: joint pain and swelling, dry eyes and mouth, skin tightening, Raynaud phenomenon in which the fingers turn white in the cold, muscle weakness, rash over the knuckles, or acid reflux all point towards an underlying autoimmune disease driving the lung involvement.

Types and causes

Risk is increased by smoking, older age, gastro-oesophageal reflux, and a family history of pulmonary fibrosis. A careful occupational and hobby history, including birds kept at home or on the terrace, damp walls, and air-cooler use, frequently changes the diagnosis.

How ILD is diagnosed

Diagnosis rests on combining the clinical history, imaging, blood tests and, where needed, tissue sampling. International practice is to reach the final label through a multidisciplinary discussion between the pulmonologist, radiologist and pathologist rather than by any single test.

High-resolution CT of the chest

HRCT is the central investigation. Thin slices show the pattern and distribution of disease: reticulation, ground-glass opacity, traction bronchiectasis, mosaic attenuation, nodules, or honeycombing. A confident usual interstitial pneumonia pattern on HRCT in the right clinical setting can establish idiopathic pulmonary fibrosis without a biopsy.

Lung function testing

Spirometry typically shows a restrictive pattern with reduced forced vital capacity, and the diffusing capacity for carbon monoxide is reduced, often before other measurements change. A six-minute walk test with oximetry documents exercise capacity and desaturation, and both are repeated over time to measure progression.

Blood and immunological tests

Rheumatoid factor, anti-CCP, antinuclear antibody with an extended myositis and scleroderma panel, creatine kinase, inflammatory markers and, where relevant, serum precipitins for suspected antigens help identify treatable autoimmune or hypersensitivity causes.

Bronchoscopy and biopsy

Bronchoalveolar lavage helps in suspected hypersensitivity pneumonitis, infection or malignancy. Transbronchial lung biopsy or transbronchial lung cryobiopsy can provide tissue with lower risk than surgery, and EBUS-TBNA is valuable when sarcoidosis with enlarged mediastinal nodes is suspected. Surgical lung biopsy is reserved for cases that remain unresolved after all of the above and where the result would change treatment.

Treatment of ILD

Removing the cause

If a drug, an occupational dust or an inhaled antigen is responsible, complete avoidance is the single most effective treatment and can arrest progression. This may mean rehoming birds, remediating damp, changing a workplace process or stopping a medication in consultation with the prescriber.

Anti-inflammatory and immunosuppressive therapy

Inflammatory ILDs such as connective tissue disease-associated disease, organising pneumonia, sarcoidosis and non-fibrotic hypersensitivity pneumonitis respond to corticosteroids, often with a steroid-sparing agent such as mycophenolate, azathioprine or, in systemic sclerosis and myositis, rituximab or cyclophosphamide. Treatment is shared with a rheumatologist where autoimmune disease is present.

Antifibrotic therapy

For idiopathic pulmonary fibrosis and for other ILDs that show a progressive fibrosing phenotype, antifibrotic drugs slow the decline in forced vital capacity. These medicines do not restore lost lung, so starting early preserves more function. Side effects such as diarrhoea, nausea, weight loss and abnormal liver tests are managed with dose adjustment and monitoring.

Supportive care

Supplemental oxygen for exertional or resting hypoxaemia, pulmonary rehabilitation, vaccination, treatment of reflux and pulmonary hypertension, cough management, nutritional support and psychological support all improve day-to-day life. Lung transplantation is considered early in suitable patients with progressive fibrosis, since referral should not wait until the disease is advanced.

Monitoring and acute worsening

Patients are reviewed every three to six months with symptom assessment, oximetry, spirometry and diffusing capacity, and HRCT is repeated when the clinical course changes. A sudden worsening of breathlessness over days to weeks may represent an acute exacerbation, infection, heart failure or pulmonary embolism, and requires urgent hospital assessment rather than a wait-and-watch approach.

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