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J84.114 Acute interstitial pneumonia
(Hamman-Rich syndrome)
Acute interstitial pneumonia (AIP) is an idiopathic interstitial lung disease that is clinically characterized by sudden onset of dyspnea and rapid development of respiratory failure. AIP is histologically characterized by diffuse alveolar damage with subsequent fibrosis. The definition of AIP excludes patients with acute respiratory distress syndrome (ARDS) attributable to an identifiable cause, as well as patients with underlying fibrotic lung disease or systemic disorders known to be associated with lung involvement such as connective tissue disease. Four cases of acute interstitial pneumonia (AIP) are described with special emphasis on clinical background, lung imaging and bronchoalveolar lavage findings.
A retrospective chart review of four patients with histologically-proven AIP, diagnosed between 1998 and 2000, was carried out. Clinical data, bronchoalveolar lavage (BAL) findings, high-resolution computed tomography (HRCT) and histological features were analysed.Three patients died and only one is in follow-up. HRCT showed areas of ground glass attenuation and alveolar consolidation in all patients. Histology, documented by open lung biopsy or autopsy specimens, was consistent with the organising form of diffuse alveolar damage pattern.BAL findings were characteristic, with a huge neutrophilia associated with scattered atypical type II pneumocytes collected in clusters with extracellular amorphous material (fragments of hyaline membranes) observed in two out of three cases.In this paper, four cases of acute interstitial pneumonia are reported in detail. The poor prognosis associated with this entity has been confirmed and the possible diagnostic role of the bronchoalveolar lavage is emphasised.
Acute interstitial pneumonia (AIP) is an idiopathic lung disease characterised by rapidly progressive dyspnoea developing over days to weeks . AIP is synonymous with Hamman Rich syndrome. It is defined as rapidly progressive respiratory failure occurring in patients without pre-existing lung disease or extrathoracic disorders known to be associated with lung involvement . The outcome is often fatal . The chest radiographic and high-resolution computed tomography (HRCT) scan manifestations of AIP are bilateral and sometimes patchy, and there are alveolar densities associated to areas of ground glass attenuation .
AIP radiologically and physiologically resembles acute respiratory distress syndrome (ARDS) and the term idiopathic AIP appears to be quite appropriate. AIP is frequently confused with acute multilobar infectious pneumonia, with other forms of interstitial pneumonia, such as acute exacerbation of idiopathic pulmonary fibrosis, rapidly progressive bronchiolitis obliterans-organising pneumonia or idiopathic acute eosinophilic pneumonia , with collagen-vascular diseases involving the lungs and with primary or secondary pulmonary capillaritis . Lung biopsy is confirmatory for AIP and it shows the organising form of diffuse alveolar damage (DAD) pattern . Due to the rarity of this entity, the clinical profile, laboratory data and treatment are not well defined. High-dose corticosteroids and cyclophosphamide are the drugs usually used and recently it has been reported that survivors can experience either recurrences or progressive interstitial lung disease .
To widen the knowledge in this field, a series of four cases of AIP is presented in detail here. The possible diagnostic role of bronchoalveolar lavage (BAL) is also emphasised.Acute interstitial pneumonia (AIP) is a rare and fulminant form of diffuse lung injury originally described by Hamman and Rich in 1935 . AIP is classified as an idiopathic interstitial pneumonia (IIP), and among the IIPs, it has the most acute onset and rapidly progressive course .AIP is similar in presentation to the acute respiratory distress syndrome (ARDS) and probably represents a subset of cases of idiopathic ARDS . (See "Acute respiratory distress syndrome: Clinical features, diagnosis, and complications in adults".)
The clinical presentation, diagnosis, treatment, and prognosis of AIP will be reviewed here. The other idiopathic interstitial pneumonias and the approach to patients with interstitial lung disease are discussed separately. (See "Idiopathic interstitial pneumonias: Classification and pathology" and "Approach to the adult with interstitial lung disease: Clinical evaluation" and "Approach to the adult with interstitial lung disease: Diagnostic testing".)
EPIDEMIOLOGY
AIP generally affects previously healthy individuals without a prior history of lung disease and occurs with roughly equal frequency in male and female individuals . It is not associated with cigarette smoking. Most patients are over the age of 40 years, with a mean age of 50 to 55 years .
PATHOLOGY
AIP has the histopathologic appearance of diffuse alveolar damage (DAD) . DAD is a reaction pattern that occurs in response to a number of known causes of lung injury, but in the case of AIP, it is idiopathic . DAD has characteristic temporal phases in its evolution — acute exudative, organizing proliferative, and healed (or fibrotic) phases . (See "Idiopathic interstitial pneumonias: Classification and pathology".
AIP is a fulminant form of IIP. Although it was previously thought to represent an acute phase of UIP, some studies have suggested that it is a distinct entity.18 However, patients with documented UIP/IPF experiencing acute exacerbations can have the pathology of AIP superimposed on UIP.27
AIP presents with the abrupt onset of dyspnea followed by rapid progression to respiratory failure. The clinical, radiographic, physiological, and histological features are identical to those of the acute respiratory distress syndrome (ARDS) but without any identifiable cause. Most patients are previously healthy individuals over 40 years of age. Men and women are equally affected. A viral prodrome is common, with symptoms that include fever, nonproductive cough, and dyspnea. Laboratory studies are nonspecific. Chest radiography and HRCT show diffuse airspace opacities and ground-glass attenuation, respectively. A similar presentation may occur as the initial manifestation of a CT
AIP is characterized by diffuse interstitial fibrosis that is temporally uniform (Fig. 72.5).28 The changes are identical to the organizing phases of diffuse alveolar damage, as seen in ARDS. Within the thickened interstitial space, there is active, diffuse fibroblast proliferation similar to the focal fibroblast foci seen in UIP. If this is progressive, honeycomb change occurs. Other features of acute lung injury, which are frequently seen in AIP, are intraalveolar hyaline membranes.
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