Melanocytes/pigment disorders Flashcards
Melanocytes are derived from what embryonic layer?
Neural crest
What is the function of melanocytes?
Melanocytes produce pigment
**The melanocyte is a dendritic cell, whose dendrites extend long distances allowing it to make contact with multiple keratinocytes and transfer melanosomes (pigment)
What is a normal epidermal-melanin unit?
Melanocyte and its surrounding keratinocytes; roughly 1:10 ratio normally (varies by location and sun damage)
Where do melanocytes reside?
In the basal layer of the epidermis
What determines a person’s skin tone?
Pigmentation is dependent on the size, number, and density of melanosomes (pigment granules in keratinocytes)
**NOT dependent on the number/density of melanocytes
Describe tuberous sclerosis
- autosomal dominant genetic disorder (1/5800-1/10,000 births) but majority (2/3) are spontaneous mutations
- TSC1 (hamartin), TSC2 (tuberin) mutations
- causes non-malignant tumors of the brain, eyes, heart, kidney, skin and lungs
What are the common symptoms of tuberous sclerosis?
- facial angiofibromas (adenoma sebaceum); telangiectatic papules that develop on the central face
- periungual fibromas (Koenen’s tumors); similar lesions found along the nail folds
- shareen patch; excess growth of collagen
- hypomelanotic macules and patches (ash leaf macules); typically 3+ on the trunk in children
Describe vitiligo
- T cell mediated autoimmune disorder (destruction of melanocytes with subsequent development of depigmented patches)
- Typically acquired (NOT present at birth) and progressive
- Hair in affected area often becomes white (poliosis)
Describe oculocutaneous albinism
- genetic disorder leading to impiared melanin production
- defect in tyrosinase or related proteins
- white to yellow/red hair with light to white skin depending on type of albinism
What are ephelides?
- known as freckles (occur on sun-exposed areas of the body)
- typically small, 1-3mm in size
- darken with sun exposure (helps differentiate them from other pigmented lesions)
- a marker of UV-induced damage and are a risk factor for the development of melanoma
What are cafe aut lait macules?
- “CALM”
- well-circumscribed uniformly light to dark brown macules or patches
- typically appear in infancy or early childhood
- not uncommon to have a few (multiple CALM are rare and may be a sign of an associated syndrome e.g. neurofibromatosis)
Describe neurofibromatosis Type 1?
“Von Recklinghausen’s disease
- autosomal dominant; up to 50% spontaneous mutations (1/3000 births)
- mutations in neurofibromin
What are the symptoms of neurofibromatosis Type 1?
- multiple café-au-lait macules (CALMs) starting in childhood
- axillary and inguinal freckling
- neurofibromas; soft or rubbery papules (Plexiform neurofibromas are larger plaques that characteristically have a “bag of worms” feel when present in the skin)
Describe solar lentigo
aka age/liver spots
- tan to dark brown or black macule due to exposure to UV irradiation
- seen later in life and are often bigger, ranging in size from 5- 15 mm in size (contrast to ephelides)
- occur in sites of chronic sun exposure, and may darken with sun exposure
Describe dermal melanocytosis
aka “mongolian spot”
- blue-gray patches over the lumbosacral region of infants with darker skin types (common in Asians)
- pigment typically fades with age
- blue color secondary to melanocytes that are in the middle to lower dermis (deeper than brown lesions)
- patches tend to be larger (few cm or more), which can help distinguish them from blue nevi
What are the three types of acquired melanocytic nevi?
- compound
- junctional
- intradermal
**more histologic significance than clinical (refer to location of melanocytic nests)
How are acquired melanocytic nevi distinguished clinically?
- composed of benign proliferations of melanocytes
- distinctions are difficult to make clinically
- junctional nevi are typically flat (“young nevi”)
- intradermal nevi tend to be raised (“old nevi”)
- risk of malignant transformation to melanoma
