Pulmonology

Biology, Etiology, and Subtypes of NSIP

At a Glance

NSIP is a pattern of lung injury that may involve inflammation, scarring, or both. It can be linked to autoimmune disease, medicines, or HIV, or occur without a known cause. Cellular NSIP often responds better to treatment than fibrotic NSIP.

Understanding the biology of Non-Specific Interstitial Pneumonia (NSIP) requires looking past the name to how your lung tissue actually behaves. Unlike some diseases that attack one specific cell, NSIP is a pattern of injury—a specific way your lungs respond to being hurt or irritated ^[1]^[2].

The “Skeleton” of the Lung: Preserved Architecture

To understand NSIP, it helps to imagine your lung’s structure. The “walls” are the alveoli (tiny air sacs) where oxygen enters your blood. In advanced fibrotic lung diseases, areas of the lung can remodel into clustered cystic air spaces called honeycombing ^[3].

In NSIP, the underlying alveolar architecture of the lung is usually preserved, even though the walls of the air sacs may become thickened with inflammation or scarring ^[1]^[4]. This is a key reason why NSIP often has a more favorable outlook than some other fibrosing lung diseases: the basic structure of the lung is still intact ^[5].

Temporal Uniformity

When pathologists look at an NSIP biopsy, they often note temporal uniformity ^[1]. This means that the inflammation or scarring in the sample generally looks like it is at a similar stage of development ^[4]. This differs from the “patchwork” appearance seen in diseases like IPF, where very old scars sit right next to brand-new active areas of injury ^[6].

The Two Faces of NSIP: Cellular vs. Fibrotic

NSIP is broadly divided into two main subtypes, though many patients have a mix of both.

Cellular NSIP (cNSIP)

In this subtype, the thickening is caused primarily by inflammation—a buildup of immune cells ^[7].

Mechanism: The immune system is actively causing swelling and irritation ^[8].
Outlook: Because inflammation can often be reduced with medications like steroids, the cellular subtype generally responds better to treatment ^[2]^[1].

Fibrotic NSIP (fNSIP)

In this subtype, the lung tissue has developed permanent fibrosis (scar tissue) ^[9].

Mechanism: The body has laid down dense layers of collagen, making the lungs stiffer and harder for oxygen to pass through ^[10].
Outlook: Fibrotic NSIP carries a higher risk of progression than cellular NSIP, but prognosis depends heavily on the underlying cause, disease extent, and treatment response ^[11]. Treatment focuses on slowing or stopping new scars from forming ^[12].

Why It Happens: Secondary vs. Idiopathic

Because NSIP is a pattern, doctors act as detectives to find the underlying cause.

Secondary NSIP (A Known Cause)

In many cases, the NSIP pattern is a result of something else in the body:

Connective Tissue Diseases (CTDs): Conditions like Scleroderma, Lupus, Sjögren’s syndrome, and Myositis (muscle inflammation) are strongly associated with the NSIP pattern ^[13]^[14].
Drug Toxicity: Certain medications can irritate the lungs. Do not stop any suspected medication without consulting your prescribing doctor ^[1].
HIV: The virus or the immune response to it can trigger this pattern ^[1].

Hypersensitivity Pneumonitis (An Overlapping Disease)

Exposure to birds, molds, or certain organic dusts can cause a separate condition called Hypersensitivity Pneumonitis (HP). While HP is a distinct disease with its own diagnostic criteria, its imaging and pathology features can closely mimic or overlap with NSIP ^[15]^[16]. Identifying an exposure is critical because avoiding the antigen is central to treating HP.

Idiopathic NSIP

If doctors cannot identify a trigger after a thorough evaluation, the diagnosis is Idiopathic NSIP ^[1]^[17]. Management focuses on controlling the immune response and slowing progression, while clinicians continue to monitor for any future signs of an underlying autoimmune condition ^[5].

Common questions in this guide

What does NSIP mean?

NSIP, or non-specific interstitial pneumonia, is a pattern of lung injury rather than a single known cause. In NSIP, inflammation or scarring can thicken the walls of the air sacs, while the basic lung structure is often preserved.

What is the difference between cellular and fibrotic NSIP?

Cellular NSIP is caused mainly by inflammation and often responds better to medicines such as steroids. Fibrotic NSIP involves permanent scar tissue, which can make the lungs stiffer and carries a higher risk of progression.

What can cause secondary NSIP?

Secondary NSIP may be associated with connective tissue diseases such as scleroderma, lupus, Sjögren’s syndrome, or myositis. Certain medicines and HIV can also be involved, so clinicians review medical conditions and medications when looking for a cause.

Could exposure to birds or mold indicate hypersensitivity pneumonitis instead of NSIP?

Bird, mold, and organic-dust exposure can cause hypersensitivity pneumonitis, which is a separate condition that may resemble or overlap with NSIP. Identifying the exposure is important because avoiding the responsible antigen is central to treating hypersensitivity pneumonitis.

How can the NSIP subtype affect treatment and outlook?

The subtype helps clinicians judge whether inflammation or permanent scarring is the main problem. Cellular NSIP often responds better to anti-inflammatory treatment, while fibrotic NSIP may require a focus on slowing further scarring; outlook also depends on the cause, disease extent, and treatment response.

Should I stop a medicine that might be linked to NSIP?

Do not stop a suspected medicine on your own. Discuss it with the prescribing clinician, who can review whether it could be contributing to the lung pattern and decide whether a change is safe.

Curated prompts to bring to your next appointment.

1.Based on my tests, do I have the 'cellular' or 'fibrotic' subtype of NSIP, or a mix of both?
2.Have we performed specific connective tissue disease tests to look for a secondary cause?
3.Are there any medications I am currently taking that are known triggers for the NSIP pattern?
4.How does my specific subtype influence the medications we will use to manage the disease?

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References (17)

1
Idiopathic non-specific interstitial pneumonia.
Belloli EA, Beckford R, Hadley R, Flaherty KR
Respirology (Carlton, Vic.) 2016; (21(2)):259-68 doi:10.1111/resp.12674.
PMID: 26564810
2
Nonspecific Interstitial Pneumonia: What Is the Optimal Approach to Management?
Tomassetti S, Ryu JH, Piciucchi S, et al.
Seminars in respiratory and critical care medicine 2016; (37(3)):378-94 doi:10.1055/s-0036-1583176.
PMID: 27231862
3
A Brief Guide to Interpreting Transbronchial Cryobiopsies for Diffuse Parenchymal Lung Disease.
Churg A, Wright JL, Manchen P, et al.
The American journal of surgical pathology 2025; (49(10)):1068-1077 doi:10.1097/PAS.0000000000002424.
PMID: 40396574
4
RNA Sequencing of Epithelial Cell/Fibroblastic Foci Sandwich in Idiopathic Pulmonary Fibrosis: New Insights on the Signaling Pathway.
Calabrese F, Lunardi F, Tauro V, et al.
International journal of molecular sciences 2022; (23(6)) doi:10.3390/ijms23063323.
PMID: 35328744
5
Korean Guidelines for Diagnosis and Management of Interstitial Lung Diseases: Part 3. Idiopathic Nonspecific Interstitial Pneumonia.
Lee J, Kim YH, Kang JY, et al.
Tuberculosis and respiratory diseases 2019; (82(4)):277-284 doi:10.4046/trd.2018.0092.
PMID: 31172700
6
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
7
Nonspecific Interstitial Pneumonia.
Teoh AKY, Corte TJ
Seminars in respiratory and critical care medicine 2020; (41(2)):184-201 doi:10.1055/s-0040-1708499.
PMID: 32279290
8
Comprehensive gene expression profiling identifies distinct and overlapping transcriptional profiles in non-specific interstitial pneumonia and idiopathic pulmonary fibrosis.
Cecchini MJ, Hosein K, Howlett CJ, et al.
Respiratory research 2018; (19(1)):153 doi:10.1186/s12931-018-0857-1.
PMID: 30111332
9
Biopsy in interstitial lung disease: specific diagnosis and the identification of the progressive fibrotic phenotype.
Ravaglia C, Nicholson AG
Current opinion in pulmonary medicine 2021; (27(5)):355-362 doi:10.1097/MCP.0000000000000810.
PMID: 34397611
10
Reprint of: Nonspecific interstitial pneumonia: pathologic features and clinical implications.
Myers JL
Seminars in diagnostic pathology 2018; (35(5)):334-338 doi:10.1053/j.semdp.2018.09.002.
PMID: 30249370
11
Clinical characteristics and prognostic factors of fibrotic nonspecific interstitial pneumonia.
Cho HK, Chung MP, Soo Lee K, et al.
Therapeutic advances in respiratory disease 2022; (16()):17534666221089468 doi:10.1177/17534666221089468.
PMID: 35400267
12
Presentation, diagnosis and clinical course of the spectrum of progressive-fibrosing interstitial lung diseases.
Cottin V, Hirani NA, Hotchkin DL, et al.
European respiratory review : an official journal of the European Respiratory Society 2018; (27(150)) doi:10.1183/16000617.0076-2018.
PMID: 30578335
13
High-Resolution CT Findings in Interstitial Lung Disease Associated with Connective Tissue Diseases: Differentiating Patterns for Clinical Practice-A Systematic Review with Meta-Analysis.
Drimus JC, Duma RC, Trăilă D, et al.
Journal of clinical medicine 2025; (14(17)) doi:10.3390/jcm14176164.
PMID: 40943925
14
Connective tissue disease-related interstitial lung disease (CTD-ILD) and interstitial lung abnormality (ILA): Evolving concept of CT findings, pathology and management.
Yoo H, Hino T, Hwang J, et al.
European journal of radiology open 2022; (9()):100419 doi:10.1016/j.ejro.2022.100419.
PMID: 35445144
15
Histological variability and consequences in chronic bird-related hypersensitivity pneumonitis.
Ochi J, Ohtani Y, Takemura T, et al.
Respirology (Carlton, Vic.) 2017; (22(7)):1350-1356 doi:10.1111/resp.13070.
PMID: 28513923
16
Advances in Concept and Imaging of Interstitial Lung Disease.
Yanagawa M, Han J, Wada N, et al.
Radiology 2025; (315(2)):e241252 doi:10.1148/radiol.241252.
PMID: 40358445
17
Interstitial pneumonia with autoimmune features.
Santhanam S, Mohanasundaram K, Krishnan S
The journal of the Royal College of Physicians of Edinburgh 2020; (50(3)):247-255 doi:10.4997/JRCPE.2020.307.
PMID: 32936097

This page is for informational purposes only and does not constitute medical advice. A pulmonologist or other treating clinician should interpret your NSIP findings, possible causes, and treatment options.

Get notified when new evidence is published on Non-specific interstitial pneumonia.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.

Guide Contents