The mildest cold injury is frostnip. Affected areas are numb, swollen, and red. Treatment is rewarming, which causes pain and itching. Rarely, mild hypersensitivity to cold persists for months to years, but there is no permanent damage to underlying tissues.
Prolonged exposure to wet cold can cause immersion foot. Peripheral nerves and the vasculature are usually injured; muscle and skin tissue may be injured in severe cases.
Initially, the foot is pale, edematous, clammy, cold, and numb. Tissue maceration may occur if patients walk extensively. Rewarming causes hyperemia, pain, and often hypersensitivity to light touch, which can persist for 6 to 10 weeks. Skin may ulcerate, or a black eschar may develop. Autonomic dysfunction is common, with increased or decreased sweating, vasomotor changes, and local hypersensitivity to temperature change. Muscle atrophy and dysesthesia or anesthesia may occur and become chronic.
Immersion foot can be prevented by not wearing tight-fitting boots, keeping feet and boots dry, and changing socks frequently.
Immediate treatment is rewarming by immersing the affected area in warm (40 to 42° C) water, followed by sterile dressings. Nicotine should be avoided. Chronic neuropathic symptoms are difficult to treat; amitriptyline may be tried (see Neuropathic Pain: Treatment).
Localized areas of erythema, swelling, pain, and pruritus result from repeated exposure to damp nonfreezing cold; the mechanism is unclear. Blistering or ulceration may occur. Chilblains most commonly affects the fingers and pretibial area and is self-limited. Occasionally, symptoms recur. Younger women are most commonly affected, some of whom may have Raynaud's phenomenon or underlying autoimmune disorders (eg, systemic or cutaneous lupus erythematosus).
Endothelial and neuronal damage results in vasospasm and exaggerated sympathetic response when exposed to cold. Nifedipine 20 mg orally 3 times a day, limaprost 20 mcg orally 3 times a day (not available in the USA), or corticosteroids (oral, eg, prednisolone 0.25 mg/kg twice a day, plus topical corticosteroids) may be effective for refractory pernio. Sympatholytic drugs and avoidance of nicotine may also help.