[Diagnostic approach in diffuse infiltrative lung diseases].

Infiltrative lung diseases (ILD) include more than 130 diseases. Chronic and acute forms of ILD must be differentiated. In each group, cases with a known cause or with an unknown cause have to be individualized. For the physician, the distinctive sign of ILD is the evidence of diffuse pulmonary opacities on chest X rays or a suggestive pattern on pulmonary function tests. The diagnosis of chronic ILD depends on epidemiologic data ("a priori" probabilities), anamnestic informations, clinical and radiological (radiography and tomodensitometry) findings which make possible to consider a diagnosis of high probability in at least 60% of cases and reduce the gamut of hypothesis in the others. Other investigations (blood, endoscopy, broncho-alveolar lavage and sometimes surgical lung biopsy) lead to the final diagnosis. Most frequent chronic ILD are sarcoidosis, idiopathic pulmonary fibrosis and connective disease associated ILD. In case of acute ILD, diagnostic procedures depend on the severity of the disease and symptomatic treatment is urgent. The main lung lesion is either oedema or alveolitis. Main acute ILD are respectively cardiogenic oedema, lesional oedema, intra-alveolar hemorrhage, infectious ILD and acute eosinophilic pneumonia. The diagnostic approach depends on the presence of an initial orientation. Sometimes, several causes are associated.