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PubMed This is a summary of 17 peer-reviewed journal articles Updated

The Major Subtypes of ILD

At a Glance

Interstitial Lung Disease (ILD) is an umbrella term for over 200 conditions. Getting an accurate diagnosis of your specific subtype—such as IPF, autoimmune ILD, or hypersensitivity pneumonitis—is critical because it dictates whether you need immune-suppressing drugs or anti-scarring medications.

Interstitial Lung Disease (ILD) is an “umbrella term” for over 200 conditions. Because many of these look identical in the early stages, your medical team must categorize your condition into a specific subtype [1]. This classification is the most important step in your care because it dictates whether you need medications to calm your immune system or medications to slow down scarring [2][3].

The Four Major Subtypes

Most patients will fall into one of these four categories based on the cause and behavior of the disease:

  • Idiopathic Pulmonary Fibrosis (IPF): “Idiopathic” means the cause is unknown. IPF is a specific form of lung scarring that occurs mostly in older adults. It is characterized by a “UIP” (Usual Interstitial Pneumonia) pattern on CT scans [4]. It does not involve the immune system in a typical way, so it is treated primarily with antifibrotics [3][5].
  • Connective Tissue Disease-Associated ILD (CTD-ILD): This occurs when an autoimmune disease (like Rheumatoid Arthritis, Scleroderma, or Lupus) attacks the lungs [2]. Because the root cause is an overactive immune system, the first line of treatment is usually immunosuppressants [3][6].
  • Hypersensitivity Pneumonitis (HP): This is caused by an allergic-like reaction to inhaled substances, such as bird feathers/droppings, mold, or certain farm dusts [7]. Identifying and removing the “trigger” is the most critical part of treatment.
  • Sarcoidosis: This condition involves the growth of tiny clumps of inflammatory cells (granulomas) in the lungs [8]. While it can cause scarring, it often responds very well to steroids or other immune-calming drugs [7].

“Progressive Fibrosing ILD” (PF-ILD): A Behavior, Not a Name

In recent years, doctors have identified a specific behavior called Progressive Pulmonary Fibrosis (PPF)—also known as Progressive Fibrosing ILD (PF-ILD) [9].

This is not a separate disease. Instead, it is a “behavior trait” that can happen to any subtype [7]. If a patient with CTD-ILD or HP continues to develop more lung scarring despite standard treatment, they are said to have a “progressive phenotype” [10][11].

Why this matters: If your disease behaves this way, your doctor may add antifibrotic medications to your regimen, even if your primary diagnosis is not IPF [12][13].

Why Accurate Subtyping is Critical

Getting the subtype right is essential because the wrong treatment can be ineffective or even harmful.

Feature IPF Autoimmune (CTD-ILD) HP (Environmental)
Primary Driver Pure Scarring (Fibrosis) Immune System Attack Environmental Trigger
Main Treatment Antifibrotics [5] Immunosuppressants [3] Removal of trigger [7]
Role of Steroids Usually avoided [14] Often used first [6] Often used to calm “flare”

If a patient with IPF is incorrectly treated with heavy immunosuppressants (like a patient with Lupus would be), it can actually worsen their condition [14]. Conversely, if a patient with autoimmune ILD only receives antifibrotics, the underlying immune attack on their lungs may continue unchecked [3][15]. This is why your team uses blood tests, imaging, and sometimes biopsies to be as precise as possible [16][17].

Common questions in this guide

What are the main subtypes of Interstitial Lung Disease (ILD)?
The four most common categories are Idiopathic Pulmonary Fibrosis (IPF), Connective Tissue Disease-Associated ILD (CTD-ILD), Hypersensitivity Pneumonitis (HP), and Sarcoidosis.
Why is it so important to know my specific ILD subtype?
Your specific subtype dictates your treatment plan. Some forms of ILD require medications to calm the immune system, while others need drugs to slow down lung scarring. Receiving the wrong treatment for your specific subtype can be ineffective or even harmful.
What does Progressive Fibrosing ILD (PF-ILD) mean?
Progressive Fibrosing ILD (PF-ILD) is not a separate disease, but rather a behavior trait where lung scarring continues to worsen despite standard treatment. If your condition behaves this way, your doctor may add anti-scarring medications to your regimen.
Can my environment cause Interstitial Lung Disease?
Yes, a specific subtype called Hypersensitivity Pneumonitis is caused by an allergic-like reaction to inhaled substances such as mold, bird droppings, or farm dust. Identifying and removing these environmental triggers is the most important part of treating this subtype.
How do doctors figure out which type of ILD I have?
Your medical team will use specialized CT scans to look for specific scarring patterns, run blood tests to rule out underlying autoimmune conditions, and review your history of environmental exposures and symptoms like joint stiffness or skin rashes.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my imaging show a classic 'UIP' pattern, and how does that influence my diagnosis?
  2. 2.Which blood tests have I had to rule out autoimmune conditions, and were any of the results 'borderline'?
  3. 3.Am I being monitored for signs of 'Progressive Pulmonary Fibrosis' (PPF)? If so, what specific changes in my breathing tests or scans would trigger a change in treatment?
  4. 4.If my diagnosis is currently 'unclassifiable,' what is the plan for narrowing it down?
  5. 5.Based on my subtype, should we be starting with an immunosuppressant, an antifibrotic, or both?

Questions For You

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References

References (17)
  1. 1

    Research Progress of Interstitial Lung Disease Based on Single-Cell Sequencing Technology.

    Li S, Zhou T, Zhang J, et al.

    Canadian respiratory journal 2026; (2026()):8863968 doi:10.1155/carj/8863968.

    PMID: 41641446
  2. 2

    Management of interstitial lung disease associated with connective tissue disease.

    Mathai SC, Danoff SK

    BMJ (Clinical research ed.) 2016; (352()):h6819 doi:10.1136/bmj.h6819.

    PMID: 26912511
  3. 3

    Interstitial Lung Disease: A Review.

    Maher TM

    JAMA 2024; (331(19)):1655-1665 doi:10.1001/jama.2024.3669.

    PMID: 38648021
  4. 4

    Computed Tomography Findings Suggestive of Connective Tissue Disease in the Setting of Usual Interstitial Pneumonia.

    Chung JH, Montner SM, Thirkateh P, et al.

    Journal of computer assisted tomography 2021; (45(5)):776-781 doi:10.1097/RCT.0000000000001230.

    PMID: 34546682
  5. 5

    Patient characteristics and pharmacologic treatment patterns in antifibrotic-treated patients with fibrosing interstitial lung diseases: real-world results from a claims database.

    Kondoh Y, Ito T, Kimura H, et al.

    BMC pulmonary medicine 2025; (25(1)):253 doi:10.1186/s12890-025-03713-x.

    PMID: 40405141
  6. 6

    Recent advances in the treatment of systemic sclerosis associated interstitial lung disease.

    Kamenova A, Tzouvelekis A, Margaritopoulos GA

    Frontiers in medicine 2023; (10()):1155771 doi:10.3389/fmed.2023.1155771.

    PMID: 37035331
  7. 7

    The natural history of progressive fibrosing interstitial lung diseases.

    Kolb M, Vašáková M

    Respiratory research 2019; (20(1)):57 doi:10.1186/s12931-019-1022-1.

    PMID: 30871560
  8. 8

    Diagnostic Approach to Advanced Fibrotic Interstitial Lung Disease: Bringing Together Clinical, Radiologic, and Histologic Clues.

    Larsen BT, Smith ML, Elicker BM, et al.

    Archives of pathology & laboratory medicine 2017; (141(7)):901-915 doi:10.5858/arpa.2016-0299-SA.

    PMID: 27628326
  9. 9

    Current perspective of progressive-fibrosing interstitial lung disease.

    Kishaba T

    Respiratory investigation 2022; (60(4)):503-509 doi:10.1016/j.resinv.2022.03.004.

    PMID: 35431170
  10. 10

    Progressive fibrosing interstitial lung diseases: A new concept and indication of nintedanib.

    Makino S

    Modern rheumatology 2021; (31(1)):13-19 doi:10.1080/14397595.2020.1826665.

    PMID: 32964766
  11. 11

    Reply to Noboa-Sevilla et al.

    Vu Pugashetti J, Newton CA, Molyneaux PL, Oldham JM

    American journal of respiratory and critical care medicine 2023; (207(3)):369-370 doi:10.1164/rccm.202209-1807LE.

    PMID: 36174209
  12. 12

    Nintedanib in Progressive Fibrosing Interstitial Lung Diseases.

    Flaherty KR, Wells AU, Cottin V, et al.

    The New England journal of medicine 2019; (381(18)):1718-1727 doi:10.1056/NEJMoa1908681.

    PMID: 31566307
  13. 13

    Towards Treatable Traits for Pulmonary Fibrosis.

    Hoffman TW, Grutters JC

    Journal of personalized medicine 2022; (12(8)) doi:10.3390/jpm12081275.

    PMID: 36013224
  14. 14

    Diagnosis and Management of Fibrotic Interstitial Lung Diseases.

    Collins BF, Luppi F

    Clinics in chest medicine 2021; (42(2)):321-335 doi:10.1016/j.ccm.2021.03.008.

    PMID: 34024407
  15. 15

    Connective tissue disease-associated interstitial lung disease.

    Storrer KM, Müller CS, Pessoa MCA, Pereira CAC

    Jornal brasileiro de pneumologia : publicacao oficial da Sociedade Brasileira de Pneumologia e Tisilogia 2024; (50(1)):e20230132 doi:10.36416/1806-3756/e20230132.

    PMID: 38536980
  16. 16

    Interstitial Lung Disease in India. Results of a Prospective Registry.

    Singh S, Collins BF, Sharma BB, et al.

    American journal of respiratory and critical care medicine 2017; (195(6)):801-813 doi:10.1164/rccm.201607-1484OC.

    PMID: 27684041
  17. 17

    Management issues in rheumatoid arthritis-associated interstitial lung disease.

    England BR, Hershberger D

    Current opinion in rheumatology 2020; (32(3)):255-263 doi:10.1097/BOR.0000000000000703.

    PMID: 32141954

This page is for informational purposes only and does not replace professional medical advice. Always consult your pulmonologist or healthcare team for an accurate diagnosis of your specific interstitial lung disease subtype and an appropriate treatment plan.

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