AIP or ARDS? Not just semantics

Abstract

I read with interest the article by Kao and colleagues [1] in which the authors investigated the role of open lung biopsy in patients with early-stage acute respiratory distress syndrome (ARDS) of suspected non-infectious origin. A point that merits attention is the need to differentiate between ARDS and acute interstitial pneumonia (AIP). AIP is a rapidly progressive idiopathic interstitial pneumonia characterized by the presence of an organizing form of diffuse alveolar damage on histopathological examination of lung specimens. Although the histological pattern is indistinguishable from that found in ARDS, the term AIP is reserved for cases of unknown cause [2]. In fact, exclusion of a precipitating or etiological agent (which is usually identifiable in patients with ARDS) is one of the diagnostic criteria for AIP. The mortality from AIP is about 70% and is higher than that from ARDS [3]. Although there are no established therapies for AIP, parenteral corticosteroids, often at high doses, are used frequently. Recently Suh and colleagues [4] reported survival rates of 80% in a small series of ten patients with AIP, all of whom required mechanical ventilation (with a median positive end-expiratory pressure of 11 cmH2O) and underwent open lung biopsy (on median hospital day 4). In these patients, high-dose corticosteroid pulse therapy had been initiated (on median hospital day 3.5) after respiratory infection had been ruled out by means of an aggressive diagnostic workup (including bronchoalveolar lavage performed on median hospital day 2). The authors had postulated that the approach of aggressive diagnostics, mechanical ventilation with lung-protective strategy, and early institution of high-dose immunosuppressive therapy could have led to the improved clinical outcome [4]. In the present study, diffuse alveolar damage was seen in most of the patients who had a non-specific pathological diagnosis. Moreover, this group, in comparison with the group with a specific diagnosis, had a higher rate of treatment alteration (87% versus 56%) as well as a higher rate of hospital survival (61% versus 33%). It is possible that the trend toward improved survival that was seen in this group was a reflection of the possibility that some of these patients had AIP (rather than ARDS) and benefited from the early administration of high-dose corticosteroids.