Acute interstitial pneumonitis  is a rare, and  fulminant disease  leading to acute respiratory failure and, or death.  Acute interstitial pneumonitis is an entity of a group of Idiopathic interstitial lung diseases first described by two pathologists<unk>  and<unk> . The etiology is unknown (idiopathic). Acute interstitial pneumonitis occurs typically previously healthy individuals in the age group of 50 to 55years with out pre eexisting lung disease. It affects men and women equally.  Acute interstitial pneumonitis shows the histopathologic appearance of diffuse alveolar damage. On gross examination, lungs appear firm, heavy and have a dark red or beefy appearance and show irregular areas of consolidation and fibrosis. On microscopic examination, acute interstitial pneumonitis shows bilateral, temporal uniformity of the diffuse alveolar damage, hyaline membrane deposition and extensive fibroblastic and myofibroblastic proliferation. Acute interstitial pneumonitis may be considered as an idiopathic cause of ARDS. Acute interstitial pneumonitis must be differentiated from other diseases that present with respiratory failure and show diffuse alveolar damage on histopathological examination. These include  ARDS, acute eosinophilic pneumonitis, Infections, hypersensitivity pneumonitis, connective tissue diseases, and drug-induced lung toxicity. Patients with acute interstitial pneumonitis usually present with flu-like viral illness or upper respiratory tract infection, which progresses very rapidly to acute respiratory failure. Common symptoms include fatigue, headache, myalgia, cough, fever, and dyspnea. The acute onset of symptoms is characteristic of acute interstitial pneumonitis. Physical examination shows tachypnea, tachycardia, crackles, wheezing and signs of hypoxemia. Chest radiograph of patients with Acute interstitial pneumonitis shows bilateral airspace opacifications. Most of the patients with acute interstitial pneumonitis on HRCT will show bilateral ground-glass attenuation, traction bronchiectasis, airspace consolidation, architectural distortion. Bronchioalveolar lavage and surgical lung biopsy can be helpful in diagnosing other diseases that causing diffuse alveolar damage that present same as acute interstitial pneumonitis There is no effective treatment for acute interstitial pneumonitis, Management in general includes supportive therapy and administration of glucocorticosteroids and Immunosuppressive agents. Lung transplantation may be considered as an alternative treatment for patients with acute interstitial pneumonitis if the conventional therapy fails. Prognosis is very poor.
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