Acute Hypersensitivity Pneumonitis Associated With a High Ki-67 Proliferative Index

Hypersensitivity pneumonitis (HSP) is an interstitial lung disease caused by exposure to a large range of environmental antigens. Inhaling aerosolized particles leads to a heightened immune response. HSP comes in acute, subacute, or chronic forms, all with their own potential clinical and radiographic findings. Mycobacterium avium complex (MAC) is the most common nontuberculous mycobacteria and is known to cause HSP with certain exposures. However, although certain histologic findings can be seen with HSP, a high ki-67 proliferation index is unusual and more commonly associated with malignancy. In this report, we discuss a case of MAC that had acute HSP associated with a high ki-67 proliferative index.