A 14-year-old boy presents to dermatology for evaluation of an asymptomatic “rash” present on his arms since age 6. The condition has caught the attention of family members and teachers over the years, particularly in regard to possible contagion.
The patient is otherwise reasonably healthy, although he has asthma and seasonal allergies.
The "rash" consists of uniformly distributed and sized planar papules. Although they are tiny, averaging only 1 mm wide, they are prominent enough to be noticeable and palpable. They appear slightly lighter than the surrounding skin. Distribution is from the lower deltoid to mid-dorsal forearm, affecting both arms identically. The volar aspects and triceps of both arms are totally spared.
The patient has type IV skin.
What’s the diagnosis?