The FP recognized this to be a Becker's nevus, also known as a Becker nevus.
This nevus, which tends to occur in adolescent males, presents as a brown patch (often with hair) that is located on the shoulder, back, or submammary area. The lesion may enlarge to cover an entire shoulder or upper arm. While the nevus in this case did not have hair, it did have increased acne within the area—another feature of Becker nevus.
Although it is called a nevus, it does not actually have nevus cells and has no malignant potential. It is a type of hamartoma—an abnormal mixture of cells and tissues normally found in the area of the body where the growth occurs. Becker nevi do not become melanoma because they lack melanocytes. Therefore, there is no reason to excise them. Generally, these lesions are large and the risks of excision for cosmetic reasons outweigh the benefits.
In this case, the patient and his mother were reassured that no treatment was needed and they opted to leave it alone.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Smith M, Usatine R. Benign nevi. In: Usatine R, Smith M, Mayeaux EJ, et al. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013:945-952.
To learn more about the Color Atlas of Family Medicine, see: www.amazon.com/Color-Family-Medicine-Richard-Usatine/dp/0071769641/.
You can now get the second edition of the Color Atlas of Family Medicine as an app by clicking on this link: usatinemedia.com.