Interntitial lung disease

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"interstitial lung diseases"[MeSH Terms]

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interstitial lung disease overview diagnosis treatment American Lung Association

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Interstitial lung disease (ILD) is a group of disorders that cause inflammation and/or scarring (fibrosis) in the lung tissue around the air sacs. This makes the lungs stiff and reduces oxygen transfer.

Common symptoms

Progressive shortness of breath, initially on exertion
Persistent dry cough
Fatigue, reduced exercise tolerance
Fine “Velcro-like” crackles on chest examination
In some people, finger clubbing or low oxygen levels

Major causes and types

Idiopathic pulmonary fibrosis (IPF): progressive fibrosing ILD without a known cause
Connective-tissue disease ILD: associated with rheumatoid arthritis, systemic sclerosis, myositis, Sjögren syndrome, etc.
Hypersensitivity pneumonitis: immune reaction to inhaled antigens such as birds, mould, or farming exposures
Occupational/environmental disease: asbestos, silica, metal/wood dusts
Drug- or radiation-related ILD: for example, some chemotherapy, immunotherapy, amiodarone, nitrofurantoin
Sarcoidosis and other inflammatory ILDs

A recent systematic review also supports inhalational and occupational exposures as important ILD risk factors (2025 review).

Diagnosis

Evaluation usually includes:

Detailed history of exposures, medicines, smoking, and autoimmune symptoms
Oxygen measurement and pulmonary function tests, often showing a restrictive pattern with reduced DLCO
High-resolution CT (HRCT), which helps identify patterns such as usual interstitial pneumonia (UIP), NSIP, or hypersensitivity pneumonitis
Blood tests for autoimmune disease
Sometimes bronchoscopy, bronchoalveolar lavage, or lung biopsy, ideally after multidisciplinary review

The American Lung Association overview lists CT imaging, lung-function testing, oxygen assessment, blood testing, and selected invasive tests as part of diagnosis.

Treatment

Treatment depends on the exact ILD subtype:

Remove the cause where possible: stop smoking, avoid antigen or workplace exposure, review causative medications.
Immunosuppression may help inflammatory or autoimmune ILDs, but is not appropriate for every ILD.
Antifibrotic drugs such as nintedanib or pirfenidone may slow lung-function decline in IPF and selected progressive fibrosing ILDs.
Pulmonary rehabilitation, vaccinations, supplemental oxygen when needed, and management of reflux or pulmonary hypertension.
Lung transplantation may be considered for advanced progressive disease.

Seek urgent medical care

Urgent assessment is needed for rapidly worsening breathlessness, chest pain, blue lips, confusion, fever with low oxygen, or a sudden fall in exercise capacity.

ILD is not one diagnosis, so the HRCT pattern and cause determine prognosis and treatment.

What tests help distinguish the different types of ILD?

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"interstitial lung diseases"[MeSH Terms] AND diagnosis

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interstitial lung disease diagnosis HRCT serology bronchoalveolar lavage ATS guideline

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https://publications.ersnet.org/content/breathe/20/1/240006

No single test identifies every ILD. Diagnosis usually combines exposure and medication history, HRCT pattern, blood tests, lung physiology, and sometimes bronchoscopy or biopsy in a multidisciplinary ILD team review.

Test	What it helps distinguish
High-resolution CT (HRCT) of the chest	The most important discriminator. A UIP pattern with basal, subpleural reticulation, traction bronchiectasis, and honeycombing supports IPF after other causes are excluded. NSIP often has symmetric ground-glass change, lower-lobe reticulation, and possible subpleural sparing. Fibrotic hypersensitivity pneumonitis (HP) is suggested by air trapping, mosaic attenuation, centrilobular nodules, and the three-density pattern.
Detailed exposure history and targeted tests	Bird, mould, hot-tub, farming, occupational dust, asbestos/silica, and drug exposures may identify HP, pneumoconiosis, asbestosis, or drug-induced ILD. Serum IgG antibodies to a suspected antigen can support exposure in HP, but do not prove disease.
Autoimmune serology	ANA, rheumatoid factor, anti-CCP, ENA antibodies, myositis antibodies such as anti-Jo-1, anti-Scl-70, and ANCA can identify connective-tissue disease-associated ILD or vasculitis. A positive result must fit the clinical picture because false-positive screening results occur.
Pulmonary function tests and DLCO	Show severity and track progression. Restriction with reduced DLCO is common, but these tests generally do not reliably name the ILD subtype. Obstruction or marked air trapping can support small-airway involvement, such as HP.
6-minute walk test and oxygen assessment	Establish functional limitation and exertional desaturation. Useful for staging and follow-up, rather than distinguishing a specific ILD.
Bronchoscopy with bronchoalveolar lavage (BAL)	Helps exclude infection and can narrow the diagnosis. BAL lymphocytosis supports HP or sarcoidosis in the right setting; a high eosinophil count suggests eosinophilic pneumonia; increasingly bloody lavage suggests diffuse alveolar hemorrhage/vasculitis. BAL is supportive, not diagnostic by itself.
Echocardiography and cardiac assessment	Helps determine whether breathlessness or low DLCO may be due to pulmonary hypertension or left-heart disease rather than ILD alone.
Lung biopsy, if uncertainty remains	Transbronchial cryobiopsy or surgical lung biopsy may distinguish histologic patterns such as UIP, NSIP, organizing pneumonia, sarcoidosis, Langerhans-cell histiocytosis, or HP. It is avoided if HRCT and clinical findings already give a confident diagnosis, or if procedural risk is high.

Practical pattern-based approach

IPF: older adult, no clear exposure or autoimmune disease, HRCT shows definite/probable UIP.
CTD-ILD: autoimmune symptoms or signs plus relevant antibodies; HRCT often NSIP or UIP.
Hypersensitivity pneumonitis: credible antigen exposure + HRCT signs of small-airway disease; BAL lymphocytosis adds support.
Sarcoidosis: hilar/mediastinal lymph nodes, upper-lobe/perilymphatic nodules, compatible BAL and sometimes tissue granulomas.
Drug-induced ILD: temporal relationship to a drug, compatible imaging, and exclusion of infection and other causes.
Occupational ILD: compatible job/exposure history plus characteristic imaging, such as pleural plaques in asbestos exposure.

HRCT is central because it can separate potentially inflammatory ground-glass disease from established fibrosis and honeycombing. The European Respiratory Society review describes typical differentiating HRCT features for UIP, NSIP, and fibrotic HP (ERS imaging review). HRCT results should be interpreted alongside the history, serology, BAL, and pathology rather than in isolation.

A recent meta-analysis found that interpretation of ILD HRCT has interobserver variation, reinforcing the value of expert radiology and multidisciplinary discussion (2024 meta-analysis).

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