Introduction: An alveolar haemorrhage occurs in 12 to 29% during microscopic polyangeitis and can reveal this disease.
Exegesis: We report the case of a fifteen years old female patient with a microscopic polyangeitis which was diagnosed during the investigation of a chronic anemia with chronic asymptomatic alveolar haemorrhage and extracapillary glomerulonephritis with antineutrophil cytoplasmic antibodies positive (anti-myeloperoxydase antibodies). The good tolerance of alveolar haemorrhage is usual for children, particularly in idiopathic pulmonary haemorrhage but is exeptionnal for adults. According to some studies, thirty percent of idiopathic pulmonary haemorrhage goes to auto-immune disease.
Conclusion: This observation shows that complementary pulmonary investigations are necessary in chronic anemia when gynaecologic and digestive investigations are negative and that auto-immune investigations are judicious in the survey of idiopathic pulmonary haemorrhage.