Melanocyte Biology and Disorders of Pigmentation

Question 1

Describe the distinction among melanocytes, melanosomes and melanin.

Answer 1

melanocytes are the cells that contain melanosomes (organelles) that produce the melanin (pigment)

Question 2

What are the two types of cutaneous pigment?

Answer 2

eumelanin and pheomelanin; normal skin color results from a combination of hemoglobin, carotenoid and melanin

Question 3

As melanocytes migrate from the neural crest, what causes them to proliferate and migrate?

Answer 3

steel factor (stem cell factor) binds the c-KIT receptor on melanocytes and melanoblasts as the migrate to the skin, hair follicles, eye, ear and brain (melanoma can affect any of these structures)

Question 4

In normal skin, approximately every ___ cell in the basal layer is a melanocyte, each melanocyte contacts ____ to____ kartinocytes.

Answer 4

10th, 30-40

Question 5

Contrast depigmentation and hypopigmentation.

Answer 5

depigmentation is complete loss of pigment while hypopigmentation is do to intermediate loss of pigment

Question 6

What is the major difference in a person skin tone compared to other people?

Answer 6

no sexual or racial difference in the relative number of melanocytes, the major determinant of skin is the activity of the melanocytes as well as the number and size of melanosomes

Question 7

What is the major enzyme involved in eumelanin production?

Answer 7

tyrosinase (tyrosine being the precursor)

Question 8

What is the the function of melanosomes?

Answer 8

intracytoplasmic organelle that is the site of melanin synthesis, mature melanosomes are continuously transferred to the adjacent karatinocytes by phagocytosis

Question 9

What factors are important in eumelanogenesis?

Answer 9

ACTH, TSH, estrogen, progesterone and sun damage to keratinocytes and primarily the binding of melanocyte stimulating factor to melanocortin-1 receptor on melanocytes

Question 10

How does sun exposure cause tanning?

Answer 10

UV damage to kartinocytes results in expression of cytokines (MSH, ETI= endothelin 1 and SCF- steel factor) which signal to the melanocyte to produce more melanin by and increase in melanocyte size and tyrosinase activity

Question 11

What causes vitiligo and in what areas is it common?

Answer 11

caused by inflammation causing melanocyte destruction and depigmentation, it is common around the mouth, hands, eyes and genitals, also may koebnerize (has an excess risk of sunburn)

NOTE is associated with alopecia areata, hypothyroidism and anemia and hypothyroidism

Question 12

What is pibaldism?

Answer 12

abnormal migration of melanocyte due to a c-kit mutation which results in midline depigmentation (often a white forelock) is inherited in a autosomal dominant fashion

Question 13

What is pityriasis alba?

Answer 13

melanocyte down regulation that results in hypopigmentation and a scant scale, it is common with other atopies (may improve with time, sunscreen and moisturizing creams may be helpful)

Question 14

What is causes oculocutaneous albinism and what are the associated findings?

Answer 14

altered melanin production due to a tyrosinase defect (AR) with is associate with skin that is white, yellow, red or red-brown (dyspigmented) and ocular findings (nystagmus, photophobia and decreased visual acuity)

Question 15

What is melasma?

Answer 15

increased melanin synthesis due to hormonal influences (estrogen and progesterone of pregnancy or HR) leaves light to medium brown patchy hyperpigmentation

Question 16

What are the treatments for melasma

Answer 16

diligent sunscreen application, stop OCPs and hydorauinone (bleaching agent works best at shallow depths)

Question 17

Describe a cafe-au-lait macule?

Answer 17

an area of increased epidermal melanin which is light brown with sharp borders, may serve as a marker for NF1 (AD)

Question 18

Describe the distinguishing distribution of pigment in the case of addison’s disease.

Answer 18

bronze hyperpigemntation is generalized to both photo exposed , palmar, areolae, axillae, umbilicus, frictional sites

Question 19

Why is the wood’s lamp examination important in diagnosing disorders of pigmentation.

Answer 19

can differentiate from hypo pigmented and depigmented skin (depigemented skin is accentuated)

Question 20

Despite being common, pigmentary disorders remain difficult to treat, those relating to inflammatory disorders are treated by ?

Answer 20

stimulating melanocyt proliferation and melanin production; topical corticosteriods and phototherapy can reduce inflammation and stimulate regimentation