True. In severe cases of Rocky Mountain spotted fever (RMSF), the enlarged lesions of the rash can progress to being necrotic, which means that the tissue in the area dies due to lack of blood supply. This can also lead to a condition known as peripheral ischemia, where the blood vessels in the fingers and toes become narrowed or blocked, which can increase the risk of gangrene. Gangrene is a serious condition that occurs when the tissue dies due to lack of oxygen, and can lead to amputation or even death in severe cases. Therefore, it is important to seek prompt medical attention if you suspect you or someone you know has Rocky Mountain spotted fever.