Photo Rounds

Rash on forearm

A 7-year-old boy was brought to his family physician (FP) because his mother noticed a new linear rash on his right forearm. She said that she noticed it about 2 months earlier, after they went camping in a state park. The boy and the mother denied any itching. The mother asked if poison ivy could last that long. The boy was otherwise in good health.

What’s your diagnosis?


Rash on forearm

The FP did not recognize the rash, so she decided to do a Google search. She typed the following terms into the search box: linear hypopigmented papules on the arm of a child. Almost every result described lichen striatus.

The photographs were very similar, and the description was a great fit for the patient’s condition. Clearly, this was not poison ivy and was unrelated to the camping trip. The physician learned that lichen striatus is a benign idiopathic condition that often affects children on a single extremity. The flat-topped papules tend to run parallel to the long axis of the extremity following Blaschko lines (lines related to embryogenesis). In darker-skinned patients, the papules are often hypopigmented. The papules are usually asymptomatic and resolve on their own, over time.

The mother was reassured and happy to hear that this would go away without any treatment. The physician was delighted to have been able to make a diagnosis by using her ability to describe the rash and the “intelligence” of the search engine.

Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Smith M. Epidermal nevus and nevus sebaceous. In: Usatine R, Smith M, Mayeaux EJ, et al. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013:958-962.

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