The interstitium in the lung is the tissue that lies between the surface of the alveoli and the capillaries that surround the alveoli. In normal lungs, this tissue is very thin to allow oxygen and carbon dioxide to cross between the surface of the alveoli (air sacs) and the capillaries that carry blood. During gas exchange, oxygen is absorbed into the blood and carried throughout the body within red blood cells and carbon dioxide leaves the blood and crosses into the alveoli so it can be released when the person exhales.
If the interstitial tissue becomes thickened due to infection, inflammation or scarring, it makes it harder for oxygen and carbon dioxide to cross the interstitium, which can make the patient quite sick. Interstitial pneumonia is inflammation of the interstitial tissue (not the alveoli themselves).
In the beginning, these patients can have a dry, unproductive cough, shortness of breath, and/or a low-grade fever. Unfortunately, this form of interstitial lung disease is rapidly progressing and is often fatal.
The common diagnostic tests are chest x-ray, chest CT scan, and lung biopsy. High-resolution CT scans show patchy or geographic ground glass opacity initially, followed by architectural distortion (honeycomb appearance with small cystic spaces surrounded by fibrosis), and traction bronchiectasis (dilated airways surrounded by fibrosis). If biopsied, the histology shows diffuse alveolar damage.
Corticosteroids and other treatments are often ineffective and many patients require mechanical ventilation and intensive care support. Even with medical intervention, this is a serious form of chILD and can be fatal.