PNS & SKIN– ch. 21

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  • Schwannomas benign tumor, may occur in soft tissues, internal organs, or spinal nerve roots (e.g. CN8), related to hearing loss, Can be sporadic or familial
  • Morphology of Schwannomas most schwannomas appear as circumscribed masses abutting an adjacent nerve, has Dense Antoni A & Loose Antoni B areas
  • Dense Antoni A areas (Schwannoma) bland spindle cells w/ buckled nuclei arranged into intersecting fascicle. Cells often align to produce nuclear palisading ⇒ results in Verocay bodies (alternating bands of nuclear & anuclear areas)
  • Loose Antoni B (Schwannoma) Axons are largely excluded from the tumor & the tumor is encapsulated, Thick-walled hyalinized vessels often are present, Hemorrhage or cystic change are also seen sometimes
  • Mutation of schwannomas merlin gene – ch22, Schwannomatosis (no vestibuar scwannomas, loss of function mutation ch22)
  • NEUROFIBROMATOSIS 2 loss of function mutation Merlin gene on chromosome 22 – Familial condition where patients at risk of multiple (1) Schwannomas (2) meningiomas (3) ependymomas –
  • Neurofibromas are not a character of neurofibromatosis 2
  • Subtypes of Neurofibromas Localized cutaneous neurofibromas, Plexiform neurofibromas , Diffuse neurofibromas
  • Grow diffusely within the confines of a nerve, Surgical enucleation is difficult – often assoc. w/ lasting neurologic deficits, they are virtually pathognomonic for NF1. The plexiform neurofibromas Unlike other benign nerve sheath tumors, these tumors are associated with a small but real risk of malignant transformation.
  • Diffuse neurofibromas infiltrative proliferations that can take the form of large, disfiguring subcutaneous masses, also often associated with NF1, show an extensive infiltrative pattern of growth within the dermis and subcutis of the skin.
  • Verocay bodies Schwannoma
  • “Marble-like” appearance Malignant peripheral sheath tumors
  • Malignant peripheral sheath tumors Neoplasms seen in adults that typically show evidence of Schwann cell derivation & sometimes a clear origin from a peripheral nerve, assoc. w/ NF1, manifest as large, poorly defined soft tissue masses, anaplasia, necrosis, infiltrative growth pattern, pleomorphism & high proliferative activity
  • Neurofibromatosis type 1 Mutations in the tumor suppressor Neurofibromin ⇒ encoded on the long arm of chromosome 17 (17q), RAS – causes neurofibromas of all three main types, malignant peripheral nerve sheath tumors, optic gliomas & other glial tumors
  • Clinical features of NF1 patients with NF1 exhibit – learning disabilities, seizures, skeletal abnormalities, vascular abnormalities with arterial stenoses, pigmented nodules of the iris (Lisch nodules), & pigmented skin lesions (axillary freckling & café au lait spots) in various degrees
  • Traumatic Neuroma Non-neoplastic proliferation associated with previous injury of a peripheral nerve – Injuries that lead to the transection of axons, activate a regenerative program ⇒ characterized by sprouting & elongation of processes from the proximal axonal stump
  • Seborrheic Keratosis occurs in middle-aged or older persons found on the trunk (many) – but also in the extremities, head, neck.
  • Sign of Lesser-Trelat (Seborrheic Keratosis) Found in rare patients, hundreds of lesions may appear suddenly as a paraneoplastic syndrome OBS❗These patients may harbor internal malignancies – most commonly GI carcinomas (produce growth factors that stimulate epidermal proliferation)
  • Mutations in seborrheic Keratosis Many have activating mutations in fibroblast growth factor (FGF) receptor 3, ⇒ which has a tyrosine kinase activity that stimulates Ras & the PI3K/AKT pathways.
  • Seborrheic Keratosis “stuck-on” appearance, Horn cysts, Pseudo-horn cysts
  • Actinic Keratosis Overt malignancy of the epidermis (squamous cell carcinoma) may be preceded by a series of progressive dysplastic changes,
  • Pathogenesis of Actinic Keratosis Not sure if they all evolve to carcinoma- cause many regress or remain stable. A high fraction of them – are associated with TP53 mutations (caused by UV light–induced DNA damage)
  • Morphology of Actinic Keratosis sandpaper-like, Epidermis: lower portions show cytologic atypia (dysplasia) ⇒ often assoc. w/ hyperplasia of basal cells or with atrophy and diffuse thinning of the epidermal surface; parakeratosis, hyperkeratosis, Dermis: contains thickened, blue-gray elastic fibers (solar elastosis/asterisk) ⇒ The result of chronic sun damage. n some lesions full thickness epidermal atypia is seen – such lesions are considered forms of squamous cell carcinoma in situ (advanced lesions)
  • Squamous cell carcinoma in skin A common tumor arising on sun- exposed sites in older people, male predominance,
  • Pathogenesis of sq. cell carcinoma most common exogenous cause of cutaneous squamous cell carcinoma is UV light exposure which causes… (1) DNA damage (2) UV light (UVB in particular) may have a transient immunosuppressive effect on skin → by impairing antigen presentation by Langerhans cells. Mutation in TP53: caused by UV light-induced DNA damage (common) Activating mutation in HRAS Loss-of-function mutations in Notch receptors: transmit signals that regulate the orderly differentiation of normal squamous epithelia.
  • In situ lesion of sq. cell carcinoma (gross + micro) appear as sharply defined, red, scaling plaques; many arise from prior actinic keratoses, characterized by highly atypical cells at all levels of the epidermis, with nuclear crowding and disorganization.
  • Advanced lesions in sq. cell carcinoma nodular invasive lesions, variable scale, may ulcerate, defined by penetration of the basement membrane, show variable degrees of differentiation... – Fr. tumors with cells arranged in orderly lobules that exhibit extensive keratinization – To neoplasms consisting of highly anaplastic cells with foci of necrosis & only abortive, single-cell keratinization (dyskeratosis)
  • Actinic keratosis & Seborrheic Keratosis may evolve to squamous cell carcinoma of the skin.
  • mutation in sq. cell carcinoma of skin TP53, HRAS, Notch receptors
  • Mutations in basal cell carcinoma Hedgehog pathway – PTCH gene (gorlin), TP53 mutation
  • Gorlin syndrome Inherited defects in the PTCH gene a tumor suppressor that regulates Hedgehog pathway signalin, cause familial basal cell carcinomas
  • Palisading pattern basal cell carcinoma & scwannoma
  • Sequence of morphology that differ melanocytic nevus from melanomas Superficial & deeper nevus cells
  • Superficial nevus cells larger and tend to produce melanin pigment and grow in nests (found in Melanocytic Nevi)
  • Deeper nevus cells smaller, produce little or no pigment, and grow in cords or single cells (in Melanocytic Nevi)
  • Deepest nevus cells have fusiform contours & grow in fascicles
  • Mutations in Melanocytic Nevi BRAF (Activating mutation), RAS, NRAS
  • Morphology of Melanocytic Nevi Early lesions: “junctional nevi “ ⇒ composed of round-to-oval cells that grow in “nests” along the dermoepidermal junction, less elevated Nuclei: uniform, round, contain nucleoli with little or no mitotic activity. Later lesion: “compound nevi” ⇒ most junctional nevi grow into the underlying dermis as nests or cords of cells, more elevated Older lesions: “ intradermal nevi” ⇒ epidermal nests lost entirely,
  • Dysplastic Nevus occur on places exposed & not exposed to sun – e.g skin, oral & anogenital mucosal surfaces, esophagus, meninges, eye, can be sporadic & familial
  • Mutations in Dysplastic Nevus NRAS & BRAF
  • Morphology of Dysplastic Nevus “pebbly” surface, Bridging, Lentiginous hyperplasia, Cytologic atypia, Alterations occurring in the superficial dermis
  • superficial dermis (1) Sparse lymphocytic infiltrate (2) Melanin incontinence = release of melanin pigment that is phagocytosed by dermal macrophages (3) Linear fibrosis surrounding epidermal nests of melanocytes
  • Radial & vertical growth Key phases of tumor development
  • Radial growth of melanoma the initial tendency of a melanoma to grow horizontally within the epidermis (in situ) – for a prolonged period. Melanomas can’t metastize & don’t induce angiogenesis
  • Vertical growth of Melanoma With time, the tumor grows downward into the deeper dermal layers as an expansile mass lacking cellular maturation Announced by the dev. of a nodule in a previously flat lesion Linked to the emergence of a clone of cells w/ metastatic potential
  • mutations in Melanoma Germline mutations in the CDKN2A gene, Somatic activating mutations in the proto-oncogenes BRAF & NRAS, Loss-of-function of the tumor suppressor PTEN, Activating mutations in the c-KIT receptor tyrosine kinase
  • Morphology of Melanoma Variations in pigmentation, irregular & notched, pagetoid spread, lymphocytic infiltrate, “Cherry red” eosinophilic nucleoli,
  • ABC's of melanoma asymmetry, border, color, diameter, evolution (of a an existing nevus)
  • Excoriation Traumatic lesion breaking the epidermis and causing a red linear mark (i.e., a deep scratch); often self-inflicted.
  • Lichenification Thickened and rough skin characterized by prominent skin markings; usually the result of repeated rubbing (“Lichen Simplex Chronicus”).
  • Macule Flat, circumscribed area, 5 mm or less in diameter, distinguished from surrounding skin by coloration. If greater than 5 mm, referred to as a patch.
  • Papule Elevated dome- or flat-topped lesion 5 mm or less in diameter. If greater than 5 mm in diameter, referred to as a nodule.
  • Plaque Elevated flat-topped lesion, usually greater than 5 mm in diameter.
  • Pustule Discrete, pus-filled raised lesion.
  • Scale Dry, horny, platelike excrescence; the result of imperfect cornification.
  • Vesicle Fluid-filled raised area 5 mm or less in diameter.
  • Bullae vesicle greater than 5 mm
  • patch macule greater than 5 mm in diameter
  • Nodule papule larger than 5 mm in diamater
  • Acantholysis Loss of intercellular adhesion of keratinocytes.
  • Acanthosis (e.g. psoriasis) Diffuse epidermal hyperplasia
  • Dyskeratosis Abnormal keratinization occurring prematurely within individual cells or groups of cells below the stratum granulosum.
  • Hyperkeratosis Hyperplasia of the stratum corneum, often associated with a qualitative abnormality of keratin.
  • Lentiginous Linear melanocyte proliferation along the epidermal basal cell layer; can occur as a reactive change or as part of a melanocytic neoplasm.
  • Papillomatosis Surface elevation caused by hyperplasia and enlargement of dermal papillae.
  • Parakeratosis Keratinization characterized by retention of the nuclei in the stratum corneum. On squamous mucosal membranes, such as buccal mucosa, parakeratosis is normal.
  • Spongiosis Intercellular edema of the epidermis.
  • Quincke syndrome severe form of urticaria
  • Pressure urticaria a specific type of urticaria where lesions are found only in areas exposed to pressure (e.g. the feet or the buttocks).
  • Hereditary angioedema inherited deficiency of C1 esterase inhibitor, which results in uncontrolled activation of complement
  • Cause of urticaria Type 1 hypersensitivity (immediate)
  • Cause of erythema multiforme drugs or infections causing epithelial damage
  • Targetoid appearance Erythema multiforme
  • cause of acute eczematous dermatitis An agent e.g. poison ivy reacts with self protein that are presented to the Langerhans cells which presents it to the CD4+ t-cells (in lymph nodes) which forms cytokines, recruit more cells & cause damage of epidemis
  • The atopic triad Atopic dermatitis, allergic rhinitis, asthma
  • Cause of atopic dermatitis It's an acute eczematous caused by defects in keratinocyte barrier function, many with a genetic basis (previously thought to be caused by allergen exposure)
  • Cause of psoriasis TH17 (IL17 recruiting neutrophils), TH1 (IL1, IFgamma recruiting macrophages) & CD8+ T cells accumulate in the epidermis and start secreting cytokines & GF that induce keratinocyte proliferation
  • Auszpitz sign Psoriasis
  • psoriasis "test tubes in a rack" look caused by acanthosis
  • Koebner phenomenon psoriatic lesions can be induced in susceptible persons by local trauma – which may induce a local inflammatory response that promotes lesion development.
  • The tongue twisiting P's pruitic, purple, polygonal, planar papule & plaques in Lichen planus
  • Wickham striae the papules highlighted by white dots (often seen in lichen planus)
  • interface dermatitis” in lichen planus lesions are concentrated at the interface of the squamous epithelium & papillary dermis.
  • squamatization seen in lichen planus, The basal cells take on the appearance of the more mature cells of the stratum spinosum – as a response to damage
  • changes of chronicity in Lichen Planus (1) epidermal hyperplasia, (2) hypergranulosis (3) hyperkeratosis.
  • “prurigo nodularis “ Nodular form om lichen simplex chronicus
  • fishnet-like pattern by acantholysis pemphigus vulgaris & foliaceus
  • subcorneal blisters include pemphigus foliaceus
  • suprabasal blisters include pemphigus vulgaris
  • subepidermal blisters include bullous pemphigoid & dermatitis herpetiformis
  • cause of both pemphigus (V+F) autoimmune; IgG attacks desmolgein (1&) and causes detachement between this intercellular adhesive proteins
  • difference between pemphigus vulgaris & Foliaceus vulgaris involves both mucosal and skin surfaces – foliaceus only involves skin surfaces
  • Fogo selvagem An unusual endemic form of pemphigus foliaceus in South America associated with the bite of a black fly.
  • Cause of bullous pemphigoid Autoimmune: complement proteins & IgG deposits linearly on Epidermal basement membrane & reacts with the hemidesmosomes and the pemphigoid antigen (type 17 collagen) – recruit other cells
  • bullous pemphigoid vs. pemphigus vulgaris Bullous pemphigoid doesn't rupture easily – since it has the full layer of epidermis intact above it (subepidermal)
  • dermatitis herpetiformis Another type of autoimmune blistering disorder characterized by: (1) extremely pruritic urticaria (2) grouped vesicles
  • pemphigus vulgaris vs. dermatitis herpetiformis PV has a female predominance, is located in suprabasal layer, invoves IgG against desmoglein – dermatitis herpetiformis has male predominance, is located in the subepidermal layer & involves IgA against gluten (gliadin)
  • Melanoma is confided to the epidermis (previously know as "in situ) Clark level 1
  • Melanoma invades the papillary dermis clark level 2
  • Melanoma filling the papillary dermis but not extending to the reticular dermis clark level 3
  • Melanoma invades reticular layer clark level 4
  • Melanoma invades the deep subcutaneous layer clark scale 5

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