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Am Fam Physician. 2015;92(6):424-430

Original article: Red Rash on the Back (Photo Quiz)

Issue date: April 15, 2015

to the editor: We believe that the rash depicted in this Photo Quiz is more consistent with a diagnosis of radiation dermatitis than with irritant contact dermatitis as suggested by the authors.

A five-hour coronary stent procedure is usually associated with a significant dose of radiation. A typical threshold for radiation burns is more than 5 Gy (total body absorbed dose), although skin changes may occur with a dose of more than 2 Gy.1 Complex interventional procedures sometimes involve up to 10 Gy of radiation.

Exposure to a radiation dose exceeding the recommended threshold can lead to radiation dermatitis, diarrhea, and headache. Cutaneous radiation syndrome begins within hours of exposure and is associated with pruritus and erythema. A latent phase may then begin, which can last days to weeks. Symptoms may progress to include blistering, ulceration, and possible necrosis. In severe cases, involvement of subcutaneous tissue and fat requires skin grafts to maintain adequate tissue coverage.2

Radiation dermatitis is often misdiagnosed as contact dermatitis. The well-circumscribed rash described in this Photo Quiz is not caused by a grounding pad (which is not used in cardiac catheterization procedures); rather it is due to the source of radiation—the image intensifier in this case.

When a prolonged cardiac catheterization procedure is performed and the image intensifier is maintained in a constant radiographic projection, radiation dermatitis can occur.

Mild radiation dermatitis may be treated with topical emollients when desquamation is present, or with moderate-potency topical corticosteroids for pruritus. More severe radiation dermatitis may require protective dressings to control symptoms such as blisters and weeping, and to prevent secondary infection. High-grade radiation dermatitis warrants consultation with a radiation oncologist or dermatologist for possible tissue debridement.3 It is the responsibility of the interventional cardiologist to notify the primary care physician of any prolonged procedure involving significant radiation (more than 5 Gy) so that the condition can be recognized and treated in a timely manner.

in reply: We appreciate the interesting alternative diagnosis presented by the authors of this letter. The key element of this Photo Quiz was identifying the best diagnosis from a preselected list; therefore, even if the authors are correct, the best answer to the question remains irritant contact dermatitis.

Clinical clues strongly support irritant contact dermatitis. The rash lacks two hallmarks of significant radiation dermatitis: pain and ulceration.1 In simple catheterization procedures, a Bovie with grounding pad might not be used. However, with pathology like this one, for which a percutaneous approach is expected to fail, patients are routinely prepped for an open bypass procedure (including placement of a grounding pad) at onset to avoid a delay during conversion. The dimensions of the rash offer further evidence. The grounding pad used measures 8.9 cm × 15.2 cm, whereas the half-value layer attenuator is 10 cm × 10 cm. The patient's rectangular rash is consistent with the shape of the grounding pad.

For refractory cases with an unclear diagnosis, biopsy can help differentiate radiation and irritant contact dermatitis. The former may be distinguished by characteristic atypical keratinocytes early on, and by atypical radiation fibroblasts with higher radiation doses.2 In this case, the clinical diagnosis did not warrant biopsy, and the patient responded to therapy for irritant contact dermatitis.

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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