Hypomelanotic macules, or hypopigmented macules, are not lesions, but simply patches of skin lighter than the surrounding area. They vary in size from several millimeters to several centimeters in diameter. They also vary in shape but are generally elliptical or lance shaped (commonly called "ash leaf" shaped). These harmless "white spots," as they are sometimes called, are seen in more than 90 percent of people with TSC, and unlike many other skin lesions associated with the disorder, they are common in infants with TSC. The presence of three or more hypomelanotic macules is considered a major feature in the TSC diagnostic criteria and serves as an important sign of the disorder. In some cases, especially in people with particularly light skin, physicians may use a type of ultraviolet light known as a Wood's lamp to see hypomelanotic macules that may not be visible otherwise.
Massachusetts general hospitals