Supernumerary nipples–uropathies–Becker's nevus syndrome (also known as "SNUB syndrome") is a skin condition that may be associated with genitourinary tract abnormalities. Supernumerary nipples, also referred to as polythelia or accessory nipples, is a pigmented lesion of the skin that is present at birth. This pigmentation usually occurs along the milk lines, which are the precursors to breast and nipple development. Clinically, this congenital condition is generally considered benign, but some studies have suggested there may be an association with kidney diseases and cancers of the urogenital system. Becker's nevus typically presents as a unilateral, non-cancerous patch of skin that is hyperpigmented and has excessive hair, often occurring on the chest, shoulder, and back. The term "Becker's nevus syndrome" is used to describe Becker's nevus occurring along with other skin, musculoskeletal, or other tissue abnormalities such as supernumerary nipples. There are some reports documenting an association between supernumerary nipples, Becker's nevus syndrome, and urinary tract abnormalities, although with conflicting results. This association has been dubbed "SNUB syndrome".
Classification One factor that distinguishes supernumerary nipples from other skin lesions is that it has the histology of breast tissue, so it falls under the umbrella term of accessory breast tissue (ABT). Accessory breast tissue has a classification system depending on how the condition presents in the individual. Separate terms are used for different combinations of the presence of nipple, areola, or glandular tissue. The most common presentation, termed polythelia, is where only the nipple is present without the areola and glandular tissue. Conversely, the presence of all three components is known as polymastia, or supernumerary breasts. SNUB syndrome may be considered part of the broader category of epidermal nevus syndromes, which is described as the presence of any type of epidermal nevus together with other developmental abnormalities in the skin, eyes, brain, heart, skeletal system, or urinary or genital systems.
Signs and symptoms Individuals with SNUB syndrome will have the characteristic symptoms of Becker's Nevus, supernumerary nipples, and some type of uropathy. Becker's nevus presents as a tan or brown patch of skin that most often occurs on chest, shoulder blade, or back, although it can occur on other parts of the body. This patch of skin can develop excess growth of coarse, dark hair years after the discoloration is first discovered. The term Becker's nevus syndrome is used when an individual has a Becker's Nevus along with other developmental abnormalities. The most common abnormality is ipsilateral breast hypoplasia, where the breasts are asymmetrical in size, shape, or placement. Other abnormalities can include scoliosis, fused ribs, asymmetry in other muscles, and supernumerary nipples. When Becker's nevus syndrome presents specifically with supernumerary nipples and urogenital abnormalities, it may be referred to as SNUB syndrome. Supernumerary nipples are presented in any shape and size along the milk line at birth, and it affects more males than females. They commonly present as 2-3 mm hyper-pigmented spots below the breast, chest, or abdomen at birth. However, they can also occur on the face, neck and back. Supernumerary nipples can start growing by responding to hormone changes during adolescence, and can produce milk during pregnancy. Supernumerary nipples may be associated with kidney and vertebral malformation. There is a wide range of kidney and urinary tract abnormalities reported to be associated with Becker's nevus or supernumerary nipples. However, whether there is a true association between uropathies, Becker's nevus, and supernumerary nipples is debated in the literature.
Causes Supernumerary nipples is a rare congenital disease that may happen in both females and males. During human embryologic development, groups of cells known as ectodermal clusters grow along the milk lines to form breasts. In normal development, two ectodermal clusters will form breasts; the rest of the ectodermal clusters will regress. If the rest of the ectodermal clusters continue growing, they will form accessory nipples. The cause of Becker's nevus is not well known yet. It is thought to be a congenital condition, but the appearance of the nevus can also be influenced by intense sun exposure or an individual's androgen levels. The Becker's nevus will often become more obvious during puberty, especially in male individuals. Other studies suggest it may relate to a genetic mutation of beta-actin. Although some studies describe the association between supernumerary nipples, Becker's nevus, and urinary tract abnormalities as "SNUB syndrome", there is no clear causal relationship between the three conditions.
Diagnosis Because of the rarity of SNUB syndrome, diagnostic methods for this particular syndrome have not been thoroughly described in the literature. Therefore, this section will describe diagnostic methods used for epidermal nevus syndromes, and Becker's nevus syndrome in particular.
Skin biopsy Becker's nevus and supernumerary nipples can usually be diagnosed by visually observing the skin. However, if visual observation alone is insufficient to make a conclusive diagnosis, a skin biopsy can be performed. A small sample of skin can be removed from the nevus and examined under a microscope to analyze the cellular components. Epidermal nevi will typically contain an abnormal overgrowth of keratin-producing cells, sweat glands, and hair follicles. There is also typically increased levels of melanin in the innermost layer of the skin, causing the darker discoloration.
Urinary system evaluation Ultrasound, CT scans, and other imaging technology can be used to evaluate for kidney or bladder cancers. Urinalysis can also be performed on urine samples to evaluate for other urinary tract problems, such as hematuria.
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