An immunohistochemical study in a fatal case of acute interstitial pneumonitis (Hamman-Rich syndrome) in a 15-year-old boy presenting as sudden death.

Acute interstitial pneumonitis (AIP), also known as Hamman–Rich syndrome, is a distinct type of idiopathic interstitial pneumonia affecting patients of both genders without pre-existing lung diseases. We describe the case of a fulminant form of AIP and discuss the pathophysiological mechanisms of AIP with reference to the histological pattern. A 15-year-previously-healthy male boy presented to the Hospital with a 6-day history of malaise, fever and cough. The clinical prodromes were followed by the acute onset of increasing shortness of breath rapidly progressing in acute respiratory failure. Chest X-ray demonstrated bilateral diffuse airspace opacification; the high resolution CT confirmed the presence of bilateral, symmetric diffuse ground-glass attenuation. The patient was admitted to the intensive care unit, but died after few hours. An autopsy was performed within 24 h. The histological examination of lung specimens showed a pattern of diffuse alveolar damage. immunohistochemical, microbiological and toxicological tests were also carried out. The clinical presentation, the histological findings and the exclusion of infective, traumatic, toxic and metabolic causes of acute respiratory distress syndrome (ARDS) allowed us to conclude that the boy was affected by AIP. In conclusion, AIP is a diagnosis of exclusion. It has a mortality rate ranging about 50%, despite mechanical ventilation. In fatal cases of AIP diagnosis can be based on clinical presentation, radiological, histological and microbiological findings and can be further confirmed by immunohistochemical analysis.