October 10, 2017
2 min read

A 3-year-old female with pruritic rash on legs, torso

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Aditi Murthy
Marissa J. Perman

Patient presented with linear erythematous papules coalescing into plaques on face, neck and legs with areas of excoriation.

Source: Aditi Murthy, MD

A 3-year-old female presented to urgent care with a 1-week history of a pruritic rash on the legs and torso. On the day of her presentation, she additionally developed two new dark brown marks on her right cheek. Her family denied any trauma to the site or exposure to possible new contactants. She was constitutionally well.

Both at home and in the emergency department, multiple efforts were made to remove the dark marks with cleansers and alcohol scrubs without effect. The patient was otherwise growing and developing normally. She was not on any prescription medications.

On exam, the patient was generally well-appearing with linear erythematous papules coalescing into plaques on her face, neck and legs with areas of excoriation. Notably on the right cheek were two angulated linear brown-black macules overlying an erythematous plaque.

Can you spot the rash?

A. Atypical nevi

B. Zygomycosis

C. Rhus dermatitis

D. Non-accidental trauma

E. Ink marker


Case Discussion

“Black spot” poison ivy is an unusual and distinctive presentation of Rhus dermatitis (C), the most common form of allergic contact dermatitis in children. Rhus dermatitis is caused by exposure to poison ivy, oak or sumac, all of which are flowering plants in the genus Toxicodendron. The black spots themselves are from the oxidation of urushiol, the primary contact sensitizer in the sap of Toxicodendron plants.

As in our case, patients with Rhus dermatitis typically present with erythematous papules and plaques arranged in linear and geometric shapes at sites of exposure. The eruption can be edematous and vesicular, and is often accompanied by significant pruritus. Treatment for this condition is aimed at the underlying dermatitis with potent topical steroids and, if warranted, a course of oral prednisone. The black spots themselves cannot be removed with water, soaps or alcohols and tend to resolve over weeks. Patients are advised to wash clothing with warm soapy water to remove ongoing exposure to allergen.

Melanocytic nevi can be congenital or acquired throughout childhood. A new brown-black macule on the face of a child could certainly bring up the possibility of a melanocytic nevus. However, these lesions tend to be round, uniformly pigmented macules and papules. The rectangular shape of these lesions in our patient, along with a history of sudden appearance overnight, would make this diagnosis highly unlikely.

In an immunocompetent child, infection from opportunistic zygomycetes such as Mucor or Rhizopus would be unlikely in the differential diagnosis. These infections can acutely present with enlarging necrotic or hemorrhagic plaques in the head and neck area. Zygomycosis should be considered in the setting of immunosuppression or uncontrolled diabetes. Treatment for the zygomycoses involves surgical debridement and systemic antifungals emergently.

In a young child, new skin lesions in geometric patterns could suggest nonaccidental trauma. However, this patient’s background, pruritic, erythematous rash indicates a primary inflammatory dermatosis. Skin lesions from nonaccidental trauma can have many morphologies depending on the mechanism of the injury.

Finally, self-induced spots from ink marker could be considered in this case. However, this is less likely given the difficulty of removal and background dermatitis.

Disclosures: Murthy and Perman report no relevant financial disclosures.