Melanocytes & Pigmentation Disorders

Question 1

What triggers melanocyte proliferation / migration?

Answer 1

Steel (stem cell) factor binds c-KIT receptor on melanocytes → proliferation / migration

Question 2

Which structures contain melanocytes?

Answer 2

Skin, hair, eye, ear, and brain

Question 3

Which enzyme is most active in melanin synthesis pathway?

Answer 3

Tyrosinase

Question 4

Describe the cascade of eumelanin production

Answer 4

Sun exposure damages cells → release of a-MSH (melanocyte stimulating hormone). MSH, ACTH, TSH, estrogen, and progesterone can all bind to melanocortin 1 receptor (MC1R) → release of tyrosine releasing protein 1 → eumelanin production

Question 5

Leukoderma

Answer 5

General term including depigmentation and hypopigmentation

Question 6

Ceruloderma

Answer 6

Gray, slate, or blue discoloration due to increase in melanocytes

Question 7

Vitiligo (cause, sxs, location, histology, associated diseases, tx)

Answer 7

Autoimmune inflammation → melanocyte destruction → depigmentation (milk-white; risk of sunburn).
Common around mouth, eyes, hands, and genitals. May Koebnerize.
Histology shows complete absence of melanocytes.
Associated w/ alopecia areata, hypothyroidism, and anemia (important to ask about fatigue).
Tx w/ topical steroids, narrow band UVB, grafting, and sunscreen.

Question 8

Piebaldism (cause, sxs, timing, tx)

Answer 8

Abnormal migration of melanocyte due to autosomal dominant mutation in cKIT → midline depigmentation (milk-white) and white forelock (poliosis).
Present at birth. Ask about family history.
Tx w/ sunscreen and cosmetic blends.

Question 9

Pityriasis Alba (cause, sxs, population, tx)

Answer 9

Inflammation → melanocyte downregulation → ill-defined hypopigmentation w/ scale. Common in children and people w/ atopic dermatitis.
Tx w/ sunscreen (decreases accentuation) and emollients

Question 10

Oculocutaneous Albinism (cause, sxs, associated disease, tx)

Answer 10

Autosomal recessive tyrosinase defect → decreased melanin production.
White, yellow, red, or red-brown skin pigmentation.
Occular findings include pink iris, nystagmus, photophobia, and decreased acuity.
High risk of SCC.
Tx w/ sunscreen and cosmetic blends

Question 11

Melasma (cause, sxs, location, tx, diagnostic)

Answer 11

Increased estrogen / progesterone (pregnancy or birth control) → increased melanin synthesis → ill-defined light / brown patchy hyperpigmentation.
Often affects forehead, cheeks, and chin. May be superficial or deep.
Tx w/ sunscreen, stopping OCPs, hydroquinone (topical bleaching agent for superficial skin), laser (superficial).
Diagnose w/ Wood’s Lamp (UV / blacklight)

Question 12

Cafe-au-lait Macules

Answer 12

Increased epidermal melanin (but normal numbers of melanocytes) → uniform light brown patches w/ sharp borders

Question 13

Neurofibromatosis Type 1 (cause and sxs)

Answer 13

Autosomal dominant

>6 CALMs, neurofibromas (rubbery skin nodules), axillary freckling and Lisch nodules (iris) are other markers for NF1.

Question 14

Addison’s Disease (cause and sxs)

Answer 14

Destruction of adrenal cortex → low cortisol → high ACTH / MSH → MC1R receptor on melanocytes → bronze hyperpigmentation. Malaise, fatigue, anorexia, nausea, abd pain, diarrhea, and low BP are other signs. May be generalized or localized.

Question 15

For which diseases is a Wood’s Lamp helpful for diagnosis?

Answer 15

Used to diagnose depigmentation or hyper pigmentation. Hypopigmentation does not show up.
Diseases include erythrasma, melasma, vitiligo, and piebaldism.
Depigmented skin is accentuated in epidermis, but not dermis, allowing physician to predict success of bleaching agents (melasma).