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Environmental Exposures

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A 58-year-old man presents to the emergency department (ED) with blister formation on both feet that began 2 days ago. He denies past medical history, medication use, or drug allergies. His social history is significant for alcohol dependence and he recently became homeless. He denies any sick contacts or recent travel. Upon physical examination, the lesions are fluid-filled. His feet are grossly cyanotic and tender to the touch. His foot is shown in the figure. What is the most likely diagnosis?

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(Reproduced, with permission, from Knoop KJ, Stack LB, Storrow AB. Atlas of Emergency Medicine. New York, NY: McGraw-Hill; 2002:517.)

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a. Chilblains

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b. Frostbite

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c. Trench foot

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d. Thermal burn

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e. Herpes

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The answer is b. Frostbite usually occurs when temperatures fall below 0°C (32°F). There are three phases to the freezing injury cascade. Phase 1 (pre-freeze, without actual ice formation) includes initial skin cooling, increased blood viscosity, vasoconstriction, and microvascular leakage that causes localized edema formation. Phase 2 (freeze-thaw) occurs when extracellular crystal formation begins, thereby causing intracellular shrinkage, protein and lipid derangements, cell dehydration, and collapse of the cellular network. Finally, phase 3 (vascular stasis and progressive ischemia) involves further coagulation, interstitial leakage, cytokine release, and cell death, thus resulting in blister formation, cyanosis, and ultimately mummification of the tissue. The bullae formed may also have a hemorrhagic appearance. It is important to note that wind and moisture may increase the freezing rate. Management includes rapid rewarming in a circulating water bath with water temperatures of 37°C to 39°C. Friction massage, which furthers tissue loss, should be avoided. Rewarming is a painful procedure that requires parenteral analgesia. Patients may also have a degree of dehydration and benefit from crystalloid administration.

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Chilblains (a), also known as pernio, is an abnormal vascular response to cold resulting in erythema, itching, and inflammation of the skin. Pernio is commonly seen in the homeless population as a result of chronic dry-cold exposure and mostly affects the face, hands, and pretibial areas. Trench foot (c), also known as immersion injury, is also common in the homeless population; however does not require freezing temperatures to occur and usually presents as a loss of sensation with pallor and mottled skin that is sodden and friable. Thermal burns (d) may present with bullae formation but do not elicit cyanosis, nor is this history consistent with thermal injury. Herpes (e) is also unlikely given the distribution, history provided, and lack of contacts with similar lesions.

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