Does this brown patch on a boy’s buttock signal underlying illness?

Case: A 12-year-old boy has had this brown patch on his left buttock since birth. His mother is concerned that the patch has grown over the years, and she wants to be sure that it will not be a health concern for her son. The mother has not noticed lesions elsewhere on the child. There is no family history of skin disease.

Does this patch indicate an underlying illness? Should it be excised to avoid cancerous change?

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Clinical examination reveals an isolated, evenly pigmented, light brown patch (not  elevated) measuring 60 × 30 mm. The lesion is oval, and the margins are well-defined and regular. It has follicular prominence with apparent hypopigmentation—the hairs in the lesion are vellus (soft, white).

I believe that this lesion is a café au lait macule. However, it could be a congenital nevocellular nevus. Although café au lait macules may be present at birth, most develop in early childhood. They are flat lesions in contrast to congenital nevocellular nevi, which are usually raised, albeit there is a flat-variant in which the elevation is visible only by side lighting. Both lesions can occur anywhere on the body.

This lesion is relatively large for a café au lait macule; most are between 10 and 50 mm in diameter; however, both small (1 to 2 mm) and large (greater than 200 mm) café au lait macules have been described. They do not have any malignant potential, unlike large congenital nevocellular nevi. For children with multiple café au lait macules of varying size, investigation for associated illnesses, particularly neurofibromatosis, is warranted.

Complete surgical removal is the only effective way to remove café au lait macules and would not be appropriate for this child’s lesion. The pigmentation, which is caused by an increase of melanin in the keratinocyte, would appear to be accessible to chemical and laser destruction. Unfortunately, “bleaching agents,” such as hydroquinone, have not been effective, and the response to a variety of lasers has been poor and unpredictable.■