What are the precursor tissues for epidermis and dermis?
Epidermis derived from ectoderm, dermis from mesoderm.
Describe the initial layers seen in developing epidermis.
A basal line of surface ectoderm is present from the start. A layer of periderm forms above these cells, and gradually sloughs off as it is replaced with intermediate layers.
What is the vernix caseosa?
A white, sticky collection of periderm (and later sebum) that coats the fetal skin and separates it from the amniotic fluid.
How do melanocytes, merkel cells, and langerhans cells develop?
They migrate from basally and differentiate in the epidermis (eg neural crest cells migrate, form melanoblasts > melanocytes)
Describe its etiology & pathophysiology.
How can you distinguish it from vitiligo?
An autosomal dominant mutation of KIT proto-oncogene. This impairs migration of melanocytes resulting in nonprogressive depigmented patches.
Look at history and progression. Vitiligo is progressive, and piebaldism generally has a familial component.
Describe its etiology.
Its symptoms include deafness, heterochromia irides, and dystopia canthorum. Why would these be true?
Multiple possible genes that contribute to abnormal melanocyte development.
Heterochromia irides since melanocytes provide pigment there. It is plausible that deafness & dystopia result from abnormal neural crest cell migration--not just of melanocytes.
How does immature dermis look on histology compared to mature dermis?
Mature dermis will have papillae.
What is a port-wine stain?
What is the signifiance of port-wine stain in the area of V1?
A port-wine stain is a collection of malformed and ectatic blood vessels which occurs in <1% of newborns.
V1 port-wine stain is a sign of Sturge-weber syndrome.
Describe the neurological and ocular findings of Sturge-Weber syndrome.
Neurological: Seizures, developmental delay, migraines and cortical calcifications.
Ocular: Congenital glaucoma (threatens vision) & increased choroidal vascularity ("tomato ketchup spot").
What is the most common vascular tumor at birth?
Describe its progression.
Infantile hemangioma (4-5% incidence).
Initially a flat white patch, which grows for up to 9 months and then (incompletely) involutes.
Recall the constellations of symptoms in PHACES syndrome.
Posterior Fossa (anomalies)
Sternal clefting / Subraumbilical Raphe
How are hair follicles formed?
The epidermis extends growths down into the dermis (hair buds), which form hair bulbs. Shafts/sheaths develop from there.
Describe the two forms of sweat glands found in skin. What type of secretion do they use, and where to they secrete to?
Eccrine glands dump directly to the surface and use merocrine secretion.
Apocrine glands dump into the hair follicle and use apocrine.
Summarize the development of nails.
A nail field forms at the tip of each feature, which migrates to form the nail plate. The nail grows from the proximal nail fold to fill the plate.
*Note: Fingernails precede toenails by ~4wks.
Hypohidriotic Ectodermal Dysplasia
What is its etiology?
What are its clinical signs?
How is it treated?
Hypohidrioitic Ectodermal Dysplasia
X-linked recessive mutation in the Ectodysplasin signaling pathway.
Inability to sweat, square forehead, flat nasum, low ears, thin/dry skin & hair, hypo-anodontia/"Peg Teeth".
Avoid overheating and keep and eye on those chompers.
From what precursor are merkel cells and langerhans cells derived?
What condition discussed here causes deafness?
What condition discussed here causes seizures?
What conditions discussed here are essentially harmless?
Piebaldism, infantile hemangiomas.