Non-specific interstitial pneumonia
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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 treatment
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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Non-specific interstitial pneumonia typically tends to present in middle-aged adults 40-50 years of age 1. It may be common in the White-European population 9. The overall prevalence is higher in women due to a high association with collagen vascular disease, but the prevalence of idiopathic NSIP is similar in both genders.
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
slowly healing diffuse alveolar damage (DAD)
relapsing organizing pneumonia
immunodeficiency (mainly HIV infection) 13
immunoglobulin G4 (IgG4)-related sclerosing disease, with or without overlapping features with Rosai-Dorfman disease 13
multicentric Castleman disease 13
If there is no underlying cause, it is termed idiopathic NSIP; which is now considered a distinct entity.
Smoking is neither protective nor a risk factor for NSIP.
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.
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
interstitial thickening is due to uniform dense or loose fibrosis and mild chronic inflammation
despite fibrotic changes, lung structures are still preserved
cellular non-specific interstitial pneumonia
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.
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.
Imaging features can overlap between the cellular and fibrotic types, as well as with usual interstitial pneumonia (UIP), in as high as 30% of patients. Also, temporal changes in the pattern of HRCT findings in subsequent studies are shown in as high as 28% of cases, resulting in the change from provisional diagnosis of NSIP to UIP.
Involvement tends to be subpleural and generally symmetrical with an apicobasal gradient. Solely or predominantly upper lobe involvement or purely unilateral disease makes the diagnosis of NSIP less likely.
Common manifestations include:
tends to be a dominant feature: can be symmetrically or diffusely distributed in all zones or display a basal predominance
immediate subpleural sparing 11 is a relatively specific sign
mostly bilateral and symmetrical (~86% 14) but can be bilateral and asymmetrical (10%) or, rarely, unilateral (3%)
mostly subpleural in distribution (~68%) but can be random (21%), diffuse (8%) or, rarely, central in distribution (3%) 14
reticular opacities and irregular linear opacities (sometimes, minor subpleural reticulation), mainly in fibrotic NSIP 6,7
thickening of bronchovascular bundles: in fibrotic NSIP 6
traction bronchiectasis: associated with fibrotic NSIP
lung volume loss: particularly lower lobes
in advanced disease:
microcystic honeycombing: a relatively less common feature
The presence of the following features, although they can be seen in NSIP, should make one think about other differentials:
Treatment and prognosis
In general, non-specific interstitial pneumonia (NSIP) carries a much more favorable prognosis than a usual interstitial pneumonia (UIP) pattern, with a 90% 5-year survival rate for the cellular subtype and a ~60% (range 45-90%) 5-year survival for the fibrotic subtype. Cellular NSIP shows a better response to corticosteroids and carries a substantially better prognosis than the fibrotic type. Correct and early diagnosis has a significant impact on patient outcomes because NSIP usually responds well to corticosteroid therapy or cessation of inciting causes, e.g. drugs or organic allergens 12. Mycophenolate mofetil has also been shown to improve lung function 15.
History and etymology
It is thought to have been initially described by Katzenstein and Fiorelli in 1994 14.
The key differential is the usual interstitial pneumonia (UIP) pattern, with which there can be some overlap in imaging features 3. The features that 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 macrocystic honeycombing is practically diagnostic for UIP.
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 early NSIP pattern is associated with many other conditions.
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