Write a short note on interstitial lung disease.

Definition

ILD (diffuse parenchymal lung disease) comprises over 200 disorders characterised by inflammation and/or fibrosis of the lung INTERSTITIUM. The functional consequences are consistent: a RESTRICTIVE defect with REDUCED DLCO and exertional hypoxaemia.

Classification

Clinical Features

• PROGRESSIVE EXERTIONAL DYSPNOEA — the cardinal symptom, insidious over months to years, often attributed to age and so presenting late
• CHRONIC DRY COUGH — often distressing and refractory
• Signs: FINE END-INSPIRATORY "VELCRO" CRACKLES at the BASES — the classic sign and often the earliest abnormality; CLUBBING in ~50% of IPF and asbestosis, notably ABSENT in sarcoidosis and hypersensitivity pneumonitis; reduced expansion; cyanosis and cor pulmonale in advanced disease
• Extrapulmonary clues: skin thickening and Raynaud's (systemic sclerosis), joint deformity and nodules (rheumatoid), Gottron's papules and heliotrope rash (dermatomyositis), erythema nodosum and lupus pernio (sarcoidosis), sicca symptoms (Sjögren's), mechanic's hands

Investigations

1. HRCT — the central investigation, often diagnostic without biopsy. Pattern and distribution are the key:

2. Pulmonary function: RESTRICTIVE — reduced FVC and TLC with normal or raised FEV1/FVC, and REDUCED DLCO (often the earliest change and the best monitor of progression). Six-minute walk with oximetry demonstrates desaturation and is prognostic.

3. Bloods: autoimmune screen — ANA, ENA, rheumatoid factor, anti-CCP, myositis panel, ANCA; serum ACE and calcium; precipitins; eosinophil count; HIV and TB screening.

4. Bronchoscopy with BAL — lymphocytosis (sarcoidosis, HP, drug-induced), neutrophilia (IPF), eosinophilia; excludes infection and malignancy. Transbronchial, cryobiopsy or surgical (VATS) biopsy where uncertain.

5. MULTIDISCIPLINARY DISCUSSION — the current standard of care and the reference standard for diagnosis, bringing together physician, radiologist and pathologist.

6. Echocardiography for pulmonary hypertension.

Idiopathic Pulmonary Fibrosis

A chronic progressive fibrosing interstitial pneumonia of unknown cause, in older adults (> 60), commoner in men and smokers, with a UIP pattern. It carries the worst prognosis of the ILDs — median survival 3–5 years, comparable to many cancers. Acute exacerbations carry very high mortality.

Management

1. Treat the specific cause where one exists

• REMOVE THE ANTIGEN — occupational dusts, birds, mouldy hay; stop the causative drug; STOP SMOKING
• Immunosuppression for inflammatory and connective tissue disease-associated ILD — corticosteroids with mycophenolate, azathioprine, cyclophosphamide or rituximab
• Corticosteroids for sarcoidosis and for organising pneumonia (which responds dramatically)
• Antitubercular therapy for tuberculosis

2. ANTIFIBROTIC THERAPY — for IPF and progressive fibrosing ILD of any cause

PIRFENIDONE and NINTEDANIB slow the rate of FVC decline and are the standard of care in IPF; nintedanib is also approved for progressive fibrosing ILD and systemic sclerosis-associated ILD. They do not reverse fibrosis.

IMPORTANT: corticosteroids and immunosuppression are NOT indicated in IPF — the PANTHER-IPF trial showed prednisolone with azathioprine and N-acetylcysteine increased death and hospitalisation. Distinguishing IPF from inflammatory ILD therefore matters enormously, because the treatments are opposite.

3. Supportive care — central, not optional: long-term oxygen therapy, pulmonary rehabilitation, vaccination, treatment of reflux, management of cough, palliative care and advance care planning (consistently introduced too late), and LUNG TRANSPLANTATION — the only intervention that improves survival in IPF; refer EARLY, at diagnosis in suitable candidates.