by Katherina Baranova MD and Matthew J. Cecchini MD PhD FRCPC
March 9, 2023
Diffuse alveolar damage (DAD) is a serious and life-threatening type of acute lung injury. DAD is seen in acute respiratory distress syndrome (ARDS), which is a clinical term used to describe people with severe shortness of breath, low levels of oxygen in the blood, and fluid in the air spaces of the lungs.
DAD is a pattern of acute lung injury that has many causes. The most common causes of DAD include infections that lead to pneumonia; severe bloodstream infection (sepsis); near-drowning; inhalation injuries, such as inhaling toxic gas, vaping-induced lung injury, or smoke; drug reactions; aspiration of stomach contents or other foreign material; other forms of shock, such as severe burns; and trauma to the chest or lungs.
Your doctor will consider your symptoms, medical history, recent travel, and medications taken to determine the cause of the DAD. If no cause can be found, a diagnosis of “acute interstitial pneumonia” is made. The prognosis for patients with acute interstitial pneumonia is poor and there are no specific treatments available currently.
When a sample of lung tissue is examined under the microscope the changes associated with DAD include hyaline membrane formation, replacement of type 1 pneumocytes with type 2 pneumocytes, and thickened alveolar walls. These changes stop the lungs from functioning normally by preventing the efficient exchange of oxygen and carbon dioxide in the alveoli. This can result in severe shortness of breath and respiratory failure.
If your doctor suspects that you have DAD, they may perform a procedure called a biopsy which removes a small tissue sample for examination by a pathologist. Your pathologist will look at the tissue sample under the microscope and may order additional tests to help determine the cause.
These additional tests may include a special stain called Grocott’s methenamine silver stain (also called GMS) to look for fungal micro-organisms and immunohistochemistry to look for specific types of viruses. If no specific cause can be found, your pathologist will describe the changes seen in your biopsy and will suggest that your doctor consider these changes along with other information about you in order to make a final diagnosis. This combination of information is called clinical correlation.