Non-specific interstitial pneumonia
Non-specific interstitial pneumonia (NSIP) is the second most common morphological and pathological pattern of interstitial lung diseases. NSIP has two main subtypes:
- fibrotic type: most common, having a more dismal outcome
- cellular type: less common, but carries a much better prognosis due to a very good response to the treatments
On imaging, the most common features are relatively symmetric and bilateral ground-glass opacities with associated fine reticulations and pulmonary volume loss resulting in traction bronchiectasis. Immediate subpleural sparing, when present is considered very specific for NSIP.
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Epidemiology
Non-specific interstitial pneumonia typically tends to present in middle-aged adults, 40-50 years of age 1. It may be common in Caucasian-European populations 9. Overall prevalence is higher in women due to high association with collagen vascular diseases, but the prevalence of idiopathic NSIP is similar in both genders.
Associations
Primarily idiopathic but the morphological pattern can be seen in association with a number of conditions:
- connective tissue disorders
- other autoimmune diseases
-
drug-induced lung disease: especially chemotherapy agents 4
- thalidomide 16
- hypersensitivity lung disease
- slowly healing diffuse alveolar damage (DAD)
- relapsing organizing pneumonia
- occupational exposure
- immunodeficiency (mainly HIV infection) 13
- graft versus host disease (GVHD) 13
- immunoglobulin G4 (IgG4)-related sclerosing disease, with or without overlap features with Rosai-Dorfman disease 13
- multicentric Castleman disease 13
- myelodysplastic syndrome 13
If there is no underlying cause, it is termed idiopathic NSIP; which is now considered a distinct entity.
Smoking is not associated, and it is not a protective factor either.
Clinical presentation
The symptoms of non-specific interstitial pneumonia are - by definition - non-specific and include insidious onset of dyspnea and dry cough with a restrictive pattern of decreased lung function and reduced gas exchange capacity.
Pathology
Temporal and spatial homogeneity in a specimen is an essential feature. Historically non-specific interstitial pneumonia was divided into three groups; however, due to similar outcomes, groups II and III (mixed cellular and fibrotic and mostly fibrotic, respectively) are now both classified as fibrotic type:
- fibrotic non-specific interstitial pneumonia: more common, interstitial thickening is due to uniform dense or loose fibrosis and mild chronic inflammation; despite fibrotic changes, lung structures still preserved
- cellular non-specific interstitial pneumonia: less common; interstitial thickening is mainly due to infiltration of inflammatory cells and type II pneumocyte hyperplasia. Lung architecture is preserved 8
Important negative histological findings are the absence of acute lung injury including hyaline membranes, granulomas, organisms or viral inclusions, dominant airways disease or organizing pneumonia, eosinophils and coarse fibrosis.
Radiographic features
Plain radiograph
A chest radiograph can be normal in the early stages. There may be ill-defined or ground glass opacities with lower lobe distribution or consolidation in a patchy, reticulonodular or mixed pattern. A bilateral pulmonary infiltrative pattern with volume loss of lower lobes may be seen in those with advanced disease.
CT
Imaging features can overlap between cellular and fibrotic types as well as usual interstitial pneumonitis (UIP) in as high as 30% of patients. Also, temporal changes in the pattern of HRCT findings in subsequent studies shown in as high as 28% of cases resulted in the change of provisional diagnosis from NSIP to UIP.
Involvement tends to be subpleural and generally symmetrical with an apicobasilar gradient. Solely or predominantly upper lobe involvement or purely unilateral disease makes the diagnosis of NSIP less likely.
Common manifestations include:
- ground-glass opacities
- tends to be a dominant feature: can be symmetrically or diffusely distributed in all zones or display a basal predominance
- immediate subpleural sparing 11 - a relatively specific sign
- mostly bilateral and symmetrical (~86% 14) but can be bilateral and asymmetrical in (10%) and rarely unilateral (3%)
- mostly subpleural in distribution (~68%) but can be random (21%), diffuse (8%), and rarely central in distribution (3%) 14
- reticular opacities and irregular linear opacities (sometimes - minor subpleural reticulation) mainly with fibrotic NSIP 6-7
- thickening of bronchovascular bundles: with fibrotic NSIP 6
- traction bronchiectasis: associated with fibrotic NSIP
- lung volume loss: particularly lower lobes
- in advanced disease
- traction bronchiectasis
- consolidation
- microcystic honeycombing: a relatively less common feature
The presence of the following features, although they can be seen in NSIP, should make us think about other differentials:
Treatment and prognosis
In general, non-specific interstitial pneumonia (NSIP) carries a much more favorable prognosis than a UIP-type pattern with 90% 5-year survival rate for cellular and ~60% (range 45-90%) 5-year survival in the fibrotic subtype. Cellular NSIP shows an even better response to corticosteroids and carries a substantially better prognosis than the fibrotic type. Correct and early diagnosis has a significant impact on patients' outcome because NSIP usually responds well to the corticosteroid therapy or cessation of inciting causes like drugs or organic allergens 12. Mycophenolate mofetil (MMF) has also shown to improve lung function 15.
History and etymology
It is thought to have been initially described by Katzenstein and Fiorelli in 1994 14.
Differential diagnosis
The key differential is a usual interstitial pneumonitis (UIP) pattern, with which there can be some overlap in imaging features 3. The features which favor the diagnosis of NSIP over UIP are symmetrical bilateral ground-glass opacities with fine reticulations and sparing of the immediate subpleural space. The presence of macroscopic honeycombing is almost diagnostic for UIP.
Practical points
- it is important to carefully scrutinise the images, looking for findings such as joint or bony changes, esophageal dilatation, pleural and pericardial effusion, etc., as it has been mentioned earlier NSIP pattern is also associated with many other conditions
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- imaging techniques
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chest x-ray
-
approach
- adult
- pediatric
- neonatal
-
airspace opacification
- differential diagnoses of airspace opacification
- lobar consolidation
-
atelectasis
- mechanism-based
- morphology-based
- lobar lung collapse
- chest x-ray in the exam setting
- cardiomediastinal contour
- chest radiograph zones
- tracheal air column
- fissures
- normal chest x-ray appearance of the diaphragm
- nipple shadow
-
lines and stripes
- anterior junction line
- posterior junction line
- right paratracheal stripe
- left paratracheal stripe
- posterior tracheal stripe/tracheo-esophageal stripe
- posterior wall of bronchus intermedius
- right paraspinal line
- left paraspinal line
- aortic-pulmonary stripe
- aortopulmonary window
- azygo-esophageal recess
- spaces
- signs
- air bronchogram
- big rib sign
- Chang sign
- Chen sign
- coin lesion
- continuous diaphragm sign
- dense hilum sign
- double contour sign
- egg-on-a-string sign
- extrapleural sign
- finger in glove sign
- flat waist sign
- Fleischner sign
- ginkgo leaf sign
- Golden S sign
- Hampton hump
- haystack sign
- hilum convergence sign
- hilum overlay sign
- Hoffman-Rigler sign
- holly leaf sign
- incomplete border sign
- juxtaphrenic peak sign
- Kirklin sign
- medial stripe sign
- melting ice cube sign
- more black sign
- Naclerio V sign
- Palla sign
- pericardial fat tag sign
- Shmoo sign
- silhouette sign
- snowman sign
- spinnaker sign
- steeple sign
- straight left heart border sign
- third mogul sign
- tram-track sign
- walking man sign
- water bottle sign
- wave sign
- Westermark sign
-
approach
- HRCT
-
chest x-ray
- airways
- bronchitis
- small airways disease
-
bronchiectasis
- broncho-arterial ratio
- related conditions
- differentials by distribution
- narrowing
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tracheal stenosis
- diffuse tracheal narrowing (differential)
-
bronchial stenosis
- diffuse airway narrowing (differential)
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tracheal stenosis
- diverticula
- pulmonary edema
-
interstitial lung disease (ILD)
- drug-induced interstitial lung disease
-
hypersensitivity pneumonitis
- acute hypersensitivity pneumonitis
- subacute hypersensitivity pneumonitis
- chronic hypersensitivity pneumonitis
- etiology
- bird fancier's lung: pigeon fancier's lung
- farmer's lung
- cheese workers' lung
- bagassosis
- mushroom worker’s lung
- malt worker’s lung
- maple bark disease
- hot tub lung
- wine maker’s lung
- woodsman’s disease
- thatched roof lung
- tobacco grower’s lung
- potato riddler’s lung
- summer-type pneumonitis
- dry rot lung
- machine operator’s lung
- humidifier lung
- shower curtain disease
- furrier’s lung
- miller’s lung
- lycoperdonosis
- saxophone lung
-
idiopathic interstitial pneumonia (mnemonic)
- acute interstitial pneumonia (AIP)
- cryptogenic organizing pneumonia (COP)
- desquamative interstitial pneumonia (DIP)
- non-specific interstitial pneumonia (NSIP)
- idiopathic pleuroparenchymal fibroelastosis
- lymphoid interstitial pneumonia (LIP)
- respiratory bronchiolitis–associated interstitial lung disease (RB-ILD)
- usual interstitial pneumonia / idiopathic pulmonary fibrosis (UIP/IPF)
-
pneumoconioses
- fibrotic
- non-fibrotic
-
lung cancer
-
non-small-cell lung cancer
-
adenocarcinoma
- pre-invasive tumors
- minimally invasive tumors
- invasive tumors
- variants of invasive carcinoma
- described imaging features
- adenosquamous carcinoma
- large cell carcinoma
- primary sarcomatoid carcinoma of the lung
- squamous cell carcinoma
- salivary gland-type tumors
-
adenocarcinoma
- pulmonary neuroendocrine tumors
- preinvasive lesions
-
lung cancer invasion patterns
- tumor spread through air spaces (STAS)
- presence of non-lepidic patterns such as acinar, papillary, solid, or micropapillary
- myofibroblastic stroma associated with invasive tumor cells
- pleural invasion
- vascular invasion
- tumors by location
- benign neoplasms
- pulmonary metastases
- lung cancer screening
- lung cancer staging
-
non-small-cell lung cancer