Tuberous Sclerosis Complex (TSC) causes benign tumors to grow in a number of different regions of the body, including the skin. Experts estimate that more than 90 percent of individuals with TSC exhibit one or more of five types of these skin abnormalities, which are benign and generally harmless. However, in some cases, they may cause physical discomfort and may be psychologically distressing to people who have them.
The high frequency of skin abnormalities in people with TSC—and the relative ease of observing them—make these symptoms important in diagnosing the disorder. Physicians often base a TSC diagnosis, at least in part, on the presence of a combination of skin lesions and other abnormalities common or unique to the disorder. The five main types of skin abnormalities (in order of frequency) include:
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.
Facial angiofibromas are small reddish spots or bumps that consist of fibrous tissue and blood vessels. They are most commonly found around the nose, cheeks, and chin, often combining to form a distinctive butterfly-shaped pattern. Angiofibromas typically appear in people with TSC between age two and age five, but may arise earlier or later in life. Early on, angiofibromas tend to be relatively bright red and level with the skin surface, but over time become thicker, more fibrous, and more numerous. Although angiofibromas are unique to TSC and considered a major feature in the TSC diagnostic criteria, they are sometimes mistaken for other skin disorders, including acne. Also, because angiofibromas seldom appear in children younger than two years of age, they are of little use in diagnosing TSC in infants and very young children.
Shagreen patches are firm yellowish-red or pink nodules slightly elevated above the surrounding skin. The surface of a shagreen patch is often described as having the texture of an orange peel. Shagreen patches vary in size from a few millimeters to more than 10 cm in diameter. If present, they are nearly always found on or around the lumbar region of the back. They typically first appear before or around puberty, but are sometimes seen in children as young as six months old. The patches may increase in number over time and typically grow in proportion to body size until adulthood. Because shagreen patches are characteristic of TSC, they are considered a major feature in the TSC diagnostic criteria.
Similar to shagreen patches, forehead plaques are fibrous, flesh-colored patches raised above the surface of the surrounding skin. They arise on the forehead or scalp and vary in size from a few millimeters to several centimeters in diameter. They may be smooth or rough in texture. In some children, forehead plaques may be obvious at birth or may appear shortly after birth. In some cases, they represent the first external symptoms of TSC. Experts classify forehead plaques as angiofibromas, and like facial angiofibromas, they are considered a major feature in the TSC diagnostic criteria. Although these lesions resemble shagreen patches, they are more closely related to facial angiofibromas. As a result, the two are grouped together for the purpose of clinical diagnosis.
Periungual fibromas are flesh-colored or reddish lesions that grow around and under fingernails and toenails. These tumors generally arise from the nail bed or from the skin around the perimeter of the nail. Periungual fibromas vary in size from a few millimeters to about 1 cm in diameter. They are more common on the toes than on the fingers, where their growth may be stimulated by the rubbing of shoes. Periungual fibromas are characteristic of TSC and are considered a major feature in the diagnostic criteria, with multiple lesions being a more reliable diagnostic sign than a single lesion. However, because periungual lesions typically do not appear until puberty, their usefulness in diagnosing very young children is limited.
There are other skin lesions associated with TSC, but because none are specific to the disorder, or because they are relatively uncommon, their usefulness in diagnosing TSC is limited. These include:
- confetti-like lesions—small, lightly pigmented spots 1-2 mm in diameter
- skin tags—multiple small soft growths that protrude from the skin, especially in the neck and groin regions
- café-au-lait spots—flat, darkly pigmented spots that are more commonly associated with the genetic disorder neurofibromatosis 1, or NF1, but may be more prevalent in people with TSC than in the general public
People with TSC, or those whose physicians suspect they have the disorder, generally undergo a thorough examination by a dermatologist or physician trained to recognize the skin abnormalities described above. In some cases, a TSC diagnosis is made on the basis of skin lesions alone. However, a positive TSC diagnosis typically combines features in the skin with those found in other organs. (For more information, see Diagnosis.)
Because many TSC-related skin lesions appear after infancy—in some cases not until puberty or later—individuals with TSC, or those suspected of having it, typically undergo periodic skin examinations to identify and track the development of new lesions.