Acute interstitial pneumonitis

This code identifies an acute inflammatory condition affecting the interstitium of the lungs, characterized by rapid onset and progression. It involves inflammation of the tissue and spaces around the air sacs, rather than the air sacs themselves, leading to impaired gas exchange.

Apply this code when documentation specifies an acute interstitial pneumonitis, often presenting with sudden dyspnea, cough, and hypoxemia. Supporting clinical evidence typically includes imaging findings (e.g., ground-glass opacities, reticular patterns on CT) and lung biopsy results confirming acute interstitial inflammation.

• Differentiate from other forms of interstitial lung disease based on the acute nature and specific pathological findings.
• Ensure documentation clearly distinguishes acute interstitial pneumonitis from chronic interstitial lung diseases.
• Remember the Excludes1 note for Pneumocystis pneumonia (B59); these conditions are mutually exclusive and should never be coded together.