74
Environmental and Sports-Related Skin Diseases
Cutaneous Injury Due to Heat Exposure
Thermal Burns
• Traumatic injury to the skin caused by an external heat source.
• The depth of the burn injury depends on the temperature of and the amount of contact time with the heat source as well as the thickness of the affected skin.
• The burn depth determines the severity and classification of the injury, its potential for healing and need for surgical intervention (Table 74.1).
Table 74.1
Classification and treatment of thermal burns.
Based on the 2009 American Burn Association revised classification system for burns. http://www.ameriburn.org/Chapter14.pdf
• In 2009, the American Burn Association replaced the traditional classification of burn wounds (i.e. first-, second-, third-degree) with a system that reflects the need for surgical intervention (see Table 74.1; Fig. 74.1).
Fig. 74.1 Thermal burn. This superficial partial-thickness burn is characterized by bullae that contain serous fluid. Courtesy, Kalman Watsky, MD.
• An exact classification of the burn injury may not be possible upon initial presentation and may take up to 3 weeks to determine; burns may be deeper than initially suspected when occurring on thinner skin (e.g. in pediatric and elderly patients; on ears, volar forearms, medial thighs, and perineum).
• The extent of burn injury is expressed as a percentage of the body surface area (BSA) involved and is essential for guiding therapy and determining a patient’s disposition (e.g. hospital admission for a partial-thickness burn involving >10% BSA in an individual 10–50 years of age).
• The most accurate method for estimating BSA involvement in adults and children is the Lund–Browder chart (http://www.tg.org.au/etg_demo/phone/etg-lund-and-browder.pdf); the ‘rule of nines’ method is perhaps more expeditious in adults, but it cannot be used for children (Fig. 74.2).
Fig. 74.2 Assessing the extent of body surface area involvement in burn injuries: Rule of nines. In adults, an estimate of burn extent is often based on this surface area distribution chart. Infants and children have a relatively increased head : trunk surface area ratio and this chart is ineffective for them. These estimates are also used for primary cutaneous disorders. The most accurate method of estimating the BSA involvement of burn injury in adults and children is with the Lund–Browder chart (http://www.tg.org.au/etg_demo/phone/etg-lund-and-browder.pdf).
• General principles of treatment are outlined in Table 74.1.
Erythema Ab Igne
• Localized areas of reticulated erythema and hyperpigmentation due to chronic exposure to heat that is below the threshold for a thermal burn.
• Multiple heat sources have been implicated (Table 74.2).
Table 74.2
Heat sources reported to cause erythema ab igne.
| • Heating pads | • Steam radiators |
| • Hot water bottles | • Heated car seats |
| • Electric stove/heater | • Heated reclining chairs |
| • Open fires | • Heating blanket |
| • Coal stoves | • Hot bricks |
| • Peat fires | • Infrared lamps |
| • Wood stoves | • Microwave popcorn |
| • Sauna belt | • Laptop computer* |
* Anterior thighs >> abdomen.
Courtesy, Mary Beth Cole, MD, and Michael Smith, MD.
• Most commonly seen in the lumbosacral region (due to heating pads applied to relieve pain from degenerative spinal disease); more recently seen on the anterior thighs from heated batteries in laptop computers.
• In long-standing erythema ab igne (latency period ≥30 years) there is an associated risk of malignant degeneration, resulting in thermal keratoses and SCC.
• Early lesions: asymptomatic, initially transient, blanchable macular erythema in a broad, reticulated pattern that corresponds to the venous plexus; size and shape approximates that of the heat source (Fig. 74.3A).
Fig. 74.3 Erythema ab igne. A Early phase with pink reticulated patches predominating over reticulated hyperpigmentation. B Later phase with large area of reticulated hyperpigmentation and superimposed pink keratotic plaques centrally. A, Courtesy, Jeffrey Callen, MD; B, Courtesy, Peter Klein, MD.
• Later lesions: dusky reticulated hyperpigmentation; lesions are fixed and no longer blanchable (Fig. 74.3B).
• End stage: may become keratotic and bullae may appear.
• DDx: livedo reticularis, cutis marmorata, poikiloderma (e.g. due to CTCL, dermatomyositis, several genodermatoses); the latter has a tighter net-like pattern.
• Rx: remove the heat source; if applicable, identify and treat the underlying source of pain.
Burns Associated with MRI and Fluoroscopy
MRI
• MRI may produce first-, second-, or third-degree burns due to metal or wire contact with skin, creating a closed-loop conduction system.
• The shape and size of the burns are determined by the conductor causing the injury (e.g. circular burns under ECG electrodes).
Fluoroscopy
• Fluoroscopy, especially when performed repeatedly in patients with cardiovascular disease, may result in radiation-induced injury (radiodermatitis).
• This radiodermatitis may be acute, but with time continued changes can develop, e.g. hair loss, desquamation, permanent erythema, and ulceration (Fig. 74.4).
Fig. 74.4 Fluoroscopy-induced radiation dermatitis. The left upper back is a characteristic location for patients who have undergone attempts at coronary artery revascularization (e.g. angioplasty, stent placement). Courtesy, Jeffrey Callen, MD.
Cutaneous Injury Due to Cold Exposure
Frostbite
• Can occur when the skin temperature drops below about –2°C (28°F).
• Tissue freezing, vasoconstriction, and inflammatory mediator release are key features of its pathophysiology.
• There are four categories of severity based on depth of tissue injury; these are only recognizable upon rewarming (Fig. 74.5).
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