The Hair Erector Muscle: Order and Disorder of This Often Forgotten Structure

The document discussed the hair erector muscle (HEM), highlighting its often-overlooked role in dermatopathology. It described both passive and active disorders associated with HEM. Passive disorders included its involvement as a bystander in conditions like nevus cell permeation, keratoacanthoma infiltration, and hemangioma encroachment. Active participation of HEM was noted in conditions such as follicular processes, insect bites, and collagen-vascular diseases. Rarely, HEM was involved in myositis, myopathies, and deposit diseases. Additionally, the document mentioned HEM tumors and hamartomatous conditions, such as disorganized muscle in blue nevi and muscle mass increase in smooth muscle hamartoma. The presentation aimed to compile various disorders of HEM, which, while not diseases on their own, contributed to a range of dermatological conditions.