Melanocytes and Pigmentation Disorders

Question 1

Melanocytes

Answer 1

• Produce pigment
• Dendritic cell
  
  • Extend to multiple keratinocytes to facilitate melanin transfer
• Epidermal-melanin unit:
  
  • Melanocyte and its surrounding keratinocytes

Question 2

From where are Melanocytes derived ?

Answer 2

Neural Crest

Question 3

Pigmentation Variance

Answer 3

• Melanocyte number and density does not vary by race
• Pigmentation dependent on the size, number, and density of melanosomes (pigment granules in keratinocytes)

Question 4

Melanosome formation

Answer 4

As follows:

Question 5

Classifications of pigment

Answer 5

1. Hyperpigmentation - Darker than surrounding or normal color; increased pigment
2. Hypopigmentation - Lighter than surrounding skin; decreased pigment
3. Depigmentation - White; no pigment

• Wood’s light exam - Help differentiate “white” areas from “light” areas

Question 6

Tuberous Sclerosis (Genetics,pathophysiology, incidence, findings)

Answer 6

• Autosomal dominant genetic disorders: TSC1 (hamartin), TSC2 (tuberin) mutations
• Pathophys: Non-malignant tumors of the brain, eyes, heart, kidney, skin and lungs
• Birth incidence: 1/5800 to 1/10,000
• Findings: 3 or more hypopigmented macules (early), adenoma sebaceum (angiofibromas and fibrous plaque), shagreen patch, periungual fibromas

Question 7

Vitiligo (Mechanism, typical course, findings)

Answer 7

• Mechanism - T-cell mediated autoimmune disorder, destruction of melanocytes with subsequent development of depigmented patches
• Course - Typically acquired, progressive course is typical
• Clinical findings - Hair in affected area often becomes white (poliosis): Hands, knees, feet, genitals depigmented (typically symmetric)

Question 8

Oculocutaneous Albinism (Genetics, Mechanism, Finding)

Answer 8

• Genetic disorders (Autosomal dominant or recessive)
• Defect in tyrosinase or related proteins resulting in impaired melanin production
• White to yellow/red hair with light to white skin

Question 9

Various brown spots

Answer 9

• Ephelides - Freckles
• Cafe au lait macules
• Solar lentigo/lentignes
• Dermal melanocytosis
• Melanocytic nevi (acquired vs congenital)

Question 10

Neurofibromatosis 1 (NF1): Genetics, incidence, findings

Answer 10

• Von Recklinghausen’s disease
• Autosomal dom. mut. in neurofibromin
• Up to 50% spontaneous mutations
• Birth Incidence: 1/3000
• Skin:
  
  • Cafe-au-lait pigmentation
  • axillary/inguinal freckling
  • neurofibromas

Question 11

Solar Lentigo

Answer 11

• “Age spots/liver spots”
• Sun exposed area, larger than ephelides
• Correlated with sunburn

Question 12

Dermal Melanocytosis

Answer 12

• “Mongolian spot”
• Deeper pigment (lower dermis) creates bluish colors
• Lumbrosacral location most common - Fading over time typical in this location

Question 13

Acquired Melanocytic Nevi

Answer 13

• Subtypes: More histologic significance than clinical
  
  1. Compound
  2. Junctional
  3. Intradermal

Question 14

ABCDE of Nevi

Answer 14

• Screening for risk to melanoma: (ABCDE)
  
  1. Asymmetry
  2. Border irregularity/blurred border
  3. Color heterogenity
  4. Diameter > 6 mm *
  5. Evolution or change

* Not applicable to congenital lesions

Question 15

Large (Giant) CMN

Answer 15

• Higher risk for melanoma than smaller CMN
• Risk for neurocutaneous melanosis
  
  • Menigeal melanosis or even melanoma >20 cm in adult
• Excision often not possible

Question 16

What is the typical ratio of kerotinocytes to melanocytes?

Answer 16

10:1

(kerotinocytes:melanocytes)