NSIP refers to interstitial pneumonia that cannot be classified into the known patterns of UIP, AIP, DIP, or BOOP. Some have considered NSIP a wastebasket diagnosis. However, because these patients may have a better prognosis than patients with IPF and treatment strategies are different for NSIP than for causes of UIP, NSIP has been classified separately from other forms of interstitial pneumonia.34-37
Histologic features--Pathologically, NSIP is characterized by varying degrees of inflammation and fibrosis within the walls of alveoli.2, 34 Although the process may be patchy (with areas of normal lung interspersed), the histologic abnormalities are temporally uniform, unlike the temporal variegation characteristic of UIP histology.34 NSIP histology has been further subdivided into types I, II, and III depending on the degree of associated fibrosis. Type I NSIP consists of interstitial inflammation without fibrosis, type II NSIP by interstitial inflammation with roughly equal amounts of fibrosis, and type III NSIP by interstitial collagen deposition with minimal interstitial inflammation.37, 38
Like UIP, the histologic lesion of NSIP may be associated with certain clinical syndromes, such as connective tissue diseases, hypersensitivity pneumonitis, and organic dust or other exposures.2, 34, 36
Clinical findings--Clinically, the most common presenting complaint is dyspnea. A non-productive cough may occur. The mean duration of symptoms is usually shorter with NSIP (months) than IPF (years).34
Radiographic findings--Chest radiographs: Radiographically, NSIP may be difficult to distinguish from causes of UIP. Reticular and patchy areas ground glass opacities with a basilar, subpleural predominance are commonly encountered (figure 3 -- 46KB).10 Findings may closely resemble cases of UIP. Air space consolidation may also be seen. Lung volumes may be maintained if the lesion of NSIP is not associated with fibrosis.
HRCT: HRCT scan findings include basilar, subpleural reticular opacities consistent with intralobular interstitial thickening. Ground glass opacity is commonly seen and suggests active, treatable alveolitis when seen in the absence of discrete honeycombing (figure 4 -- 53KB). Bronchial dilation may be seen in areas of ground glass opacity; this finding generally correlates with greater amounts of fibrosis histologically (Type III NSIP).2, 10, 36, 38, 39 Honeycombing is rarely encountered, and generally suggests the diagnosis of UIP-related diseases as opposed to NSIP. It has been shown that the ground glass opacity seen with NSIP may improve markedly with treatment (figure 5 -- 27KB), unlike UIP-related illnesses.38 Although some investigators have shown that ground glass opacity may evolve into linear and reticular opacities with honeycombing on follow-up HRCT, it is unclear if untreated NSIP inexorably progresses to honeycomb lung. The extent of improvement of abnormalities on HRCT have been shown to correlate with functional improvement following treatment.40
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