**4. Pernio (frostbite or chilblains)**

Pernio (frostbite or chilblains) is a vascular disease affecting small vessels of the peripheral skin. Persistent low temperature (cooling) or freezing of the skin causes pernio. Persistent hypoxia of the tissue eventually results in necrosis and ulceration. In a chronic stage, scleroderma-like change may follow. Histopathological features of pernio include mild inflammation around small vessels, peri-eccrine inflammation, and necrosis of the subcutaneous fat tissue with formation of multinucleated giant cells. The epidermis may reveal spongiosis, basal vacuolation, and

#### **Figure 2.**

*Wet gangrene (gross appearance of two cases and H&E). Infected deep irregular ulcers are formed in the back of the foot (left) and the base of the second toe after autoamputation (right). Histologically, Gram-positive cocci in the necrotic upper dermis are observed in the debridement specimen (the courtesy of Dr. Yasuhito Kaneko at Department of Dermatology, Shimada Municipal Hospital, Shimada, Japan).*

keratinocyte necrosis [12–14]. Representative features are displayed in **Figure 3**. These histopathologic pictures are seen in other vascular disorders, provoking a chronic irritative process of the skin.
