# Interstitial Lung Disease Approach

> Interstitial lung disease for NEET-PG Medicine covering the restrictive PFT pattern, UIP and NSIP on HRCT, exposure history and when biopsy is needed.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/interstitial-lung-disease-approach
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Harrison's Principles of Internal Medicine; ATS/ERS/JRS/ALAT guideline on idiopathic pulmonary fibrosis; Robbins and Cotran Pathologic Basis of Disease
- How to cite: "Interstitial Lung Disease Approach", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/interstitial-lung-disease-approach

## Direct answer

Interstitial lung disease is a group of disorders causing inflammation or fibrosis of the alveolar walls and interstitium. It presents with a restrictive pulmonary function pattern, a reduced transfer factor and bibasal crackles. The approach combines pulmonary function testing, HRCT pattern recognition and a careful exposure, drug and autoimmune history. Surgical lung biopsy is reserved for patients whose HRCT pattern remains indeterminate after multidisciplinary review.

## What you must remember

- **Restrictive pattern:** reduced total lung capacity and forced vital capacity with a normal or raised FEV1/FVC ratio; the diffusing capacity (DLCO) is reduced in parenchymal disease.
- **UIP pattern:** subpleural basal reticulation with honeycombing and no features suggesting another diagnosis; it is the hallmark of idiopathic pulmonary fibrosis.
- **NSIP pattern:** bilateral, symmetric ground-glass opacity with reticulation and preserved subpleural lung; common in connective tissue disease.
- **Organising pneumonia:** patchy, often peribronchovascular and migratory consolidation that responds to corticosteroids.
- **Hypersensitivity pneumonitis:** mosaic attenuation with centrilobular nodules and air trapping on expiratory images, linked to birds, mould or farm dust.
- **Antifibrotic therapy:** pirfenidone and nintedanib slow the decline in forced vital capacity in idiopathic pulmonary fibrosis.

## A 63-year-old ex-smoker with Velcro crackles

A 63-year-old ex-smoker has exertional breathlessness for a year and fine end-inspiratory crackles at both bases. Pulmonary function testing shows a restrictive pattern with a reduced DLCO, and the high-resolution CT shows subpleural basal honeycombing without features suggesting another diagnosis.

That is a definite UIP pattern in a suitable clinical setting, and the workup then follows these steps.

1. **Medication history:** Drug causes such as amiodarone, methotrexate and nitrofurantoin are excluded first.
2. **Autoantibodies:** Antinuclear antibody, anti-CCP, myositis panel and ANCA are checked, because a connective tissue disease can mimic the pattern.
3. **Diagnosis:** A definite UIP pattern means a biopsy is not needed, and idiopathic pulmonary fibrosis is diagnosed after known causes are excluded.
4. **Antifibrotic therapy:** An antifibrotic agent is the treatment, and oxygen is prescribed if resting or exertional saturation falls.
5. **Avoid steroids:** Corticosteroids are not used as maintenance therapy in idiopathic pulmonary fibrosis because they do not help and are associated with harm.
6. **Change course for mosaic attenuation:** If the HRCT had shown mosaic attenuation instead, the approach would move to exposure history, bronchoalveolar lavage and a search for an antigen source.

## Where the examiner tests the pattern

Three pattern traps recur on this topic.

- **Trap:** equating reticulation with fibrosis. — **Correct:** ground-glass opacity is usually inflammatory and may be reversible, whereas honeycombing defines established fibrosis, and traction bronchiectasis supports it.
- **Trap:** confusing upper-zone with basal patterns. — **Correct:** silicosis causes upper-zone nodules and may show eggshell calcification of hilar nodes, and in India it is commonly linked with tuberculosis in stone-quarry and mining workers; asbestosis is basal, with pleural plaques as a clue.
- **Trap:** attributing lymphocytosis on lavage to idiopathic pulmonary fibrosis. — **Correct:** bronchoalveolar lavage lymphocytosis points to sarcoidosis or hypersensitivity pneumonitis, and sarcoidosis produces perilymphatic nodules and bilateral hilar lymphadenopathy.

## Frequently asked questions

### Which HRCT pattern defines usual interstitial pneumonia?

Usual interstitial pneumonia is defined on HRCT by subpleural basal reticulation with honeycombing and no features suggesting another diagnosis. It is the pattern of idiopathic pulmonary fibrosis, and biopsy may be unnecessary when the pattern is definite in the right clinical setting.

### Which PFT pattern suggests interstitial lung disease?

A restrictive pattern with reduced total lung capacity, a normal or raised FEV1/FVC ratio and a reduced DLCO suggests interstitial lung disease. Obesity and chest wall disease can also restrict the lungs, but these usually keep the DLCO normal.

### When is lung biopsy needed in interstitial lung disease?

Lung biopsy is needed when the HRCT pattern is indeterminate or inconsistent with clinical findings after multidisciplinary discussion. Histological confirmation then guides therapy, particularly when immunosuppression is being considered.

### Why are corticosteroids avoided in idiopathic pulmonary fibrosis?

Corticosteroids do not benefit idiopathic pulmonary fibrosis and are associated with harm, so they are not used as maintenance therapy. Antifibrotic drugs such as pirfenidone or nintedanib are the treatment of choice.