Diffuse alveolar damage (DAD) is a histologic term used to describe specific changes that occur to the structure of the lungs during injury or disease.

Most often DAD is described in association with the early stages of acute respiratory distress syndrome (ARDS).

[5] Once the initial insult has damaged the alveoli and begun the process of DAD, the condition will typically progress in three phases: exudative, proliferative, and fibrotic.

That being said, the histologic finding of DAD is often associated with the clinical syndrome ARDS but it can also be seen in conditions such as acute interstitial pneumonia (essentially ARDS but without a known inciting cause), acute exacerbation of idiopathic pulmonary fibrosis, and primary graft dysfunction after lung transplant.

In order to make a diagnosis of DAD a biopsy of the lung must be obtained, processed, and examined microscopically.

[12] Of the patients who succumb to ARDS, the most common cause of death is septic shock with multi organ dysfunction syndrome.