The Clinical Picture

Whiplash-shaped acute rash

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A previously healthy 32-year-old man presented to the emergency room with a persistent, nonpruritic rash on his trunk, which had suddenly appeared 2 days after he ate Chinese food.

Figure 1. A widespread streaked rash with a scratch-like appearance over the patient's back.

Physical examination revealed multiple crosslinked linear plaques that appeared like scratches over his chest, back, and shoulders (Figures 1 and 2). He had no dermatographism, and his scalp, nails, palms, and soles were not affected. He had no signs of lymphadenopathy or systemic involvement.

Figure 2. Closer inspection of the lesions showed intensely erythematous linear plaques with a pseudo­vesicular surface.

Basic blood and urinary laboratory testing, blood cultures, and serologic studies showed normal or negative results.

Given the presentation and results of initial testing, his rash was diagnosed as flagellate erythema, likely due to shiitake mushroom intake. The diagnosis does not require histopathologic confirmation.

The rash resolved spontaneously over the next 2 weeks with use of a topical emollient and without scarring or residual hyperpigmentation.

FLAGELLATE ERYTHEMA

Flagellate erythema is a peculiar cutaneous eruption characterized by the progressive or sudden onset of parallel linear or curvilinear plaques, most commonly on the trunk. The plaques are typically arranged in a scratch pattern resembling marks left by the lashes of a whip.1 In contrast to other itchy dermatoses and neurotic excoriations that may present with self-induced linear marks, flagellate erythema appears spontaneously.

Drug-related causes, disease associations

Originally described in association with bleomycin treatment, flagellate erythema is currently considered a distinct feature of several dermatologic and systemic disorders, and therefore the ability to recognize it is valuable in daily practice.2 In addition to bleomycin analogues and anticancer agents such as peplomycin,1 bendamustine,3 and docetaxel,4 physicians should consider shiitake dermatitis5 and other less commonly reported associations such as dermatomyositis,6 lupus,7 Still disease,8 and parvovirus infection.9

Diagnostic features

The diagnosis of flagellate erythema is mainly based on the morphologic features of the clinical lesions.1 Shiitake dermatitis and flagellate erythema related to rheumatologic disease usually present with more inflammatory and erythematous plaques. Chemotherapy-induced flagellate rash typically has a violaceous or purpuric coloration, which tends to leave noticeable hyperpigmentation for several months.2

Skin biopsy may be necessary to distinguish it from similar-looking dermatoses with different histologic findings, such as dermatographism, phytophotodermatitis, erythema gyratum repens, and factitious dermatoses, which may require specific treatments or be related to important underlying pathology.1,2

Treatment

Treatment includes both specific treatment of the underlying cause and symptomatic care of the skin with topical emollients and, in cases of associated pruritus, oral antihistamines. The patient should also be reassured about the self-healing nature of shiitake dermatitis rash.5

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