Non-specific interstitial pneumonia

Non-specific interstitial pneumonia (NSIP) is the second most common morphological and pathological pattern of the interstitial lung disease. NSIP has two main subtypes, cellular type which is less common but carries much better prognosis due to very good response to the treatments and the more common fibrotic type which has more dismal outcome. 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 is present is considered very specific for NSIP. However, the diagnosis of NSIP still remains one of the biggest challenges for not only radiologists but also pulmonists and pathologists; studies showed correct diagnosis by chest radiologist varies between 65-85%. 

It 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.

Symptoms are non-specific and include insidious onset of dyspnoea and dry cough with restrictive pattern of decreased lung function and reduced gas exchange capacity. 

Temporal and spatial homogeneity in a specimen is a key feature. Historically NSIP is divided into three groups; however due to similar outcome groups II and III (mixed cellular and fibrotic and mostly fibrotic, respectively) are now both classified in fibrotic type:

Important negative histological findings are the absence of acute lung injury including hyaline membranes, granulomas, organisms or viral inclusions, dominant airways disease or organising pneumonia, eosinophils and coarse fibrosis.

Associations

Primarily idiopathic but the morphological pattern can be seen in association with a number of conditions:

If there is no underlying cause, it is termed idiopathic NSIP; which is now considered a specific entity.

Smoking is not associated and it is not a protective factor either.

Plain radiograph

Chest radiograph can be normal in 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 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 change of provisional diagnosis from NSIP to UIP.

Involvement tends to be sub-pleural and generally symmetrical with apico-basilar gradient. Solely or predominantly upper lobe involvement or purely unilateral disease makes the diagnosis of NSIP less likely. 

Common manifestations include:

The presence of following features, although they can be seen in NSIP, should make us think about other differentials:

In general NSIP carries a much more favourable prognosis than a UIP type pattern with 90% 5 years survival rate for cellular and 45-90% 5 years survival in fibrotic subtype. Cellular NSIP shows even better response to corticosteroids and carries a substantially better prognosis than the fibrotic type. Correct and early diagnosis has 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.

It is thought to have been initially described by Katzenstein and Fiorelli in 1994 14.

The key differential is a usual interstitial pneumonitis (UIP) pattern: where there can be some overlap in imaging features 3. The features which favour the diagnosis of NSIP over UIP are symmetrical bilateral ground glass opacities with fine reticulations and sparing of the immediate subpleural space. Presence of macroscopic honeycombing is almost diagnostic for UIP.

Also it is important to carefully scrutinise the images, looking for findings such as joint or bony changes, esophageal dilatation, pleural and pericardial effusion, etc. cause as it has been mentioned earlier NSIP pattern is also associated with many other conditions.


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Article Information

rID: 11007
System: Chest
Synonyms or Alternate Spellings:
  • NSIP
  • Non specific interstitial pneumonia (NSIP)
  • Non specific interstitial pneumonitis
  • Non specific interstitial pneumonitis (NSIP)
  • Non-specific interstitial pneumonias

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    Case 1: typical example of fibrotic type
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    NSIP - HRCT
    Case 2: with background SLE
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    NSIP
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    Case 4: NSIP - initial scan
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    Case 4: NSIP - post therapy
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    Case 8: with background systemic sclerosis
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