Dermatology Flashcards
the 3 layers of the skin
epidermis - keratinocytes
dermis - CT and vessels
subcutaneous fat also called hypodermis
the 5 layers of the epidermis
“Come Let’s Get Sun Burned”
straum corneum
stratum lucidum
stratum granulosum
stratum spinosum
stratum basale - contain stem cells
stratum basale contain which type of cells
stem cells - capable of regenerating the epithelial cells
stratum spinosum
contains desmosomes - forms the spines in cells
Stratum granulosum
keratohyalin granules (causes this layer to be dark) that form keratin filaments
stratum lucidum
clear layer of dead skin cells
stratum corneum
contain anucleated cells filled with keratin filaments (tough outer layer of the skin)
processes that tend to cause leaky vessels affect what layer of the skin?
the dermis - where CT and blood vessels are located
Hyperkeratosis
thickening of the stratum corneum due to an excess of keratin
Occurs in:
Psorisas - plaque build up
Calluses on palms and soles of feet
Hyperkeratosis - thickening of the stratum corneum due to an excess of keratin
Psorisas - Hyperkeratosis - thickening of the stratum corneum due to an excess of keratin
Parakeratosis - hyperkeratosis + RETAINED NUCLEI in the stratum corneum; indicates hyperproliferation
Occurs in:
psoriasis
malignancies
Parakeratosis
hyperkeratosis + RETAINED NUCLEI in the stratum corneum; indicates hyperproliferation
Occurs in:
psoriasis
malignancies
Hypergranulosis is a classic feature seen in which skin pathology?
lichen planus
Hypergranulosis
increased thickening of the stratum granulosum; classic finding in lichen planus
Spongiosis - fluid accumulation (edema) of the epidermis; seen in eczema and many other skin disorders
Spongiosis
fluid accumulation (edema) of the epidermis; seen in eczema and many other skin disorders
Acantholysis
loss of connections between keratinocytes - often loss of desmosomes; “rounded” keratinocytes that are detached, floating freely in the epidermis
key feature in - pemphigus vulgaris
Acantholysis is a ket feature in which skin pathology?
pemphigus vulgaris
Acantholysis - loss of connections between keratinocytes - often loss of desmosomes; “rounded” keratinocytes that are detached, floating freely in the epidermis - can lead to the formation of a blister
key feature in - pemphigus vulgaris
Acanthosis
diffuse epidermal hyperplasia - elongated rete ridges and **SPINOUS layer thickening
Which layer of the epidermis thickens to form elongated rete ridges in acanthosis?
stratum spinosum
Acanthosis Nigricans
darkened/hyperpigmented plaques on skin in skin folds (classically the neck and axillae); hyperkeratosis is present - associated with insulin resistance and very rarely associated with malignancy (gastric adenocarcinoma)
macula
flat lesion that is <1 cm (m=mini)
ex: freckles - increased amount of melanin
patch
flat lesion that is >1 cm
ex: stork bite birthmark
a mole/nevus - an example of a papule - raised lesion that is < 1 cm
papule
a raised lesion that is < 1 cm
ex: a mole/nevus
a plaque - a raised lesion that is > 1 cm (psoriasis)
plaque
a raise lesion that is > 1 cm
maculopapular rash
mixtures of flat (macules) and raised (papules) small lesions - “morbilliform” - looks like measles
Common in:
Drug rash, scarlet fever, syphillis and rubella
vesicle
fluid filled lesion that is < 1 cm
ex: chickenpox
bulla
fluid filled lesion that is > 1 cm
ex: bullous pemphigoid
pustule
fluid filled variant that is filled with purulent “pus-filled vesicle” - has white center
Ex: pustular psoriasis or acne
acne - an example of an pustule - fluid filled variant that is filled with purulent “pus-filled vesicle” - has white center
Wheal
**SMOOTH, elevated papule or plaque; surrounded by erythema (redness); **ITCHY - caused by dermal edema
component of urticaria (hives) - allergic reaction
Scale
secondary lesion that is caused by peeling/flaking of the stratum corneum
commonly seen in psoriasis
Wheal a **SMOOTH, elevated papule or plaque; surrounded by erythema (redness); **ITCHY - caused by dermal edema
component of urticaria (hives) - allergic reaction
Crust
secondary skin lesion caused by *dried exudate of a primary skin lesion
ex: Impetigo
Wheal a **SMOOTH, elevated papule or plaque; surrounded by erythema (redness); **ITCHY - caused by dermal edema
component of urticaria (hives) - allergic reaction
These itchy, erythematous, scaly plaques on the extensors of the knees will have which characteristic feature on histology?
Acanthosis - diffuse epidermal hyperplasia with thickening of the stratum spinosum and elongated rete ridges as seen in this pt w/ plaque psoriasis
the type of collagen in the basement membrane?
type IV collagen - Goodpasture’s and Alport syndrome
Tight Junctions
seals two cell membranes together - functions as a barrier to paracellular movement - found near apical membrane - proteins occluding and claudin
Adherens Junctions
found below tight junctions - anchors cells to one another; form belt around cells - major protein **cadherins (link actin filaments)
E-caherins is lost in some forms of breast cancer
Desmosomes
“spots” of cell-cell attachments (not belts); common in skin - attach to intermediate filaments made upon keratin
Hemidesmosomes
similar to desmosomes - attach epithelial to basement membranes - linked by integrins
Gap Junctions
channel connections using connexions - allow small molecules to pass
Acne
inflammation of hair follicles and sebaceous glands (enlarge at puberty); exocrine glands in the dermis that secrete sebum (gives oily texture to skin); androgens increase sebum production (men w/ lots of acne at puberty)
Sebum = optimal growth medium for bacteria = **Propionibacterium acnes
*Comedones allow bacterial growth
Acne Treatment
benzoyl peroxide - breaks down keratin and is bactericidal to P. acnes
Antibiotics - clindamycin and erythromycin
Retinoids (Vitamin A derivatives)
Isotretinoin
Accutane (13 cis-retinoic acid) - a version of Vitamin A used in acne treatment - decreases keratin production; it is HIGHLY teratogenic (need to take OCP and take a pregnancy test prior)
Seborrheic dermatitis
red plaques with scale (flaky skin) occurs on the face and scalp; associated with fungal infection by Malassezia
tx: antifungals and corticosteroids
melanocytes nevus
moles - benign neoplasm of melanocytes - tan/brown lesions with a uniform color; usually round or oval and less than 6mm
Pseudofolliculitis barba
Razor bumps or shave bumps
inflammation of trapped hairs; associated w shaving; common in black men
Psoriasis
autoimmune chronic inflammatory skin disorder with well-demarcated plaques on extensor surfaces; usually described pink or salmon color; strongly associated w/ HLA-C allele
Findings:
Acanthosis
Parakeratotic scaling (retained nuclei)
Stratum granulosum - thinned or absent
Auspitz sign - scale breaks and causes bleeding (due to dermis being close to the surface of the skin)
Other findings:
nail pitting
1/3rd develop psoriatic arthritis
Auspitz sign
classic sign seen in psoriasis when a scale breaks and there is bleeding due to the dermis being close to the surface of the skin
nail pitting seen in psoriasis
Rosacea
inflammatory skin disorder that affects light-skinned pts (older/elderly); chronic redness of nose and cheeks; look similar to acne but no comedones
Other features:
facial flushing (triggered by alcohol) and phymatous rosacea (skin hypertrophy)
Rosacea - inflammatory skin disorder that affects light-skinned pts (older/elderly); chronic redness of nose and cheeks; look similar to acne but no comedones
phymatous rosacea - skin hypertrophy (thickened skin) commonly located on the nose - seen in pts with Rosacea
Seborrheic keratosis
common benign tumors due to the proliferation of **immature keratinocytes - occurs in older patients (trunk area) and arise spontaneously
appear “stuck on”
in biopsy you will see “horn cyst” cyst filled with keratin
“horn cyst” cyst filled with keratin as seen in Seborrheic keratosis
Leser-Trelat-Sign
“explosive onset” of multiple itchy Seborrheic keratosis (SK) lesions; probably caused by cytokines - associated w/ malignancy (gastric adenocarcinoma)
an explosive one of Seborrheic keratosis around the trunk area, what you do next in this pt?
look for evidence of gastric adenocarcinoma - this the Leser-Trelat-Sign
Verrucae
warts - cellular proliferation triggered by HPV
Koilocytosis
cytoplasmic clearing “halos” around the nucleus - characteristic feature of infection with HPV
Koilocytosis - cytoplasmic clearing “halos” around the nucleus - characteristic feature of infection with HPV
Verruca Vulgaris
verruca = warts and vulgaris = common
Cutaneous warts - most common manifestation of HPV infection, transmitted by contact with virus (hands) - will see epidermal hyperplasia and koilocytosis on histology
Erythema Nodosum
painful red nodules on the skin (shin); type IV hypersensitivity rxn; a form of panniculitis (inflammation of subcutaneous fat)
Findings:
Septal panniculitis
Triggers:
Infection (Strep)
Crohn’s
Sarcoidoisis
Septal panniculitis - inflammation of the septa of fat between dermis and fascia - a finding in erythema nodosum
Lichen Planus
chronic inflammatory skin disorder that occurs in adults and resolves spontaneously; associated w/ Hep C
Purple papules and plaques that are ITCHY - common in the wrists and ankles b/l
Clues:
mucosal involvement - mouth, tongue, glans penis “wicked striae” - white dots/lines hypergranulosis of oral lesions
Histology: “sawtooth” pattern of rete ridges
Sawtooth pattern of the rete ridges
lichen planus
Pityriasis Rosea
acute, self-limited skin rash that occurs as an eruption of lesions that resolves within 2-3 months, no tx req - cause is unknown
Skin finding “Herald patch” w/ a “Christmas tree distribution”
pt who has a herald patch that is followed by rashes on the back in a Christmas tree pattern, what should you suspect and how should you tx?
Pityriasis Rosea - self-limited skin rash that resolves within 2-3 months, no tx req
Superficial Burn
1sr degree burn - epidermis only; painful, red and blanch w/ pressure (looks like sunburn); no blistering - heals w/i 7 days; there is minimal tx required
Superficial partial thickness burn
2nd degree burn - epidermis and some dermis - often forms blisters; red and painful - blanch w/ pressure; heals 7-21 days
Deep Partial Thickness Burn
2nd degree burn - epidermis and most of dermis - erythematous and often yellow/white; almost ALWAYS blister - easily unroofed (tissues moves) - painful to pressure ONLY and do NOT blanch; long time to heal >21days - forms a scar
Full thickness burn
4th degree burn - entire epidermis and dermis and some underlying tissue (fat, fascia or muscle); it is PAINLESS; scarring w/ wound contracture
Sunburn
DELAYED inflammatory response to skin in respite to UVR **UVB range is the most damaging to our skin
UV radiation - DNA damage - apoptosis
“sunburn cells” - keratinocytes undergoing apoptosis
Melanin
black/brown pigment that gives color to skin and hair; synthesized by melanocytes (derived from neural crest cells - same as neural ganglia and adrenal medulla); found in basal layer of epidermis;
Albinism
AR disorder where there is absent/reduced melanin synthesize due to decreased tyrosinase activity (converts tyrosine to DOPA quinone then gets converted to melanin): NOTE - the # of melanocytes are NORMAL
Increased risk for sunburns and skin cancer due to lack of UV light protection
Melasma
ACQUIRED hyperpigmentation (think opposite of albinism) - irregular areas of tan/dark macules on face - most common in women w/ dark complexions in sun-exposed areas of the face
Triggers:
UV light w/ an onset of pregnancy and OCP - commonly called the “mask of pregnancy” and resolves after pregnancy
Vitiligo
acquired localized pigment disorder (pts are asymptomatic) - autoimmune destruction of melanocytes - tx w/ steroids and immunosuppressants
pt goes to the beach and comes back and notices that they are suntanned over their entire body except in a couple of localized regions, what skin disorder should you suspect?
Vitiligo - in light skinned individuals there is failure to tan in localized regions
in dark-skinned pts there are obvious areas of depigmentation
Vitiligo - autoimmune destruction of melanocytes - tx w/ steroids and immunosuppressants - associated w/ autoimmune thyroid disease
Blood Blister
traumatic bleeding in dermis - the epidermis is intact
Angiosarcomas
rare tumor of blood or lymph vessels
sarcoma = mesenchyme origin
angio = blood vessel
usually in the head and neck and arise from the dermis layer
occur in the liver after exposure to vinyl chloride and in the breast after radiation therapy
Bacillary Angiomatosis
Zoonotic infection by Bartonella (lice or cats) - usually in end stage HIV and AIDs pt - eruption of red/purple nodules
would see neutrophils/lymphocytes on biopsy
Kaposi Sarcoma
Caused by the (Human Herpesvirus-8) HHV-8; common in AID/HIV pts - key difference from Bacillary Angiomatosis is you will only see lymphocytes on biopsy (no neutrophils)
Pyogenic Granuloma
benign vascular tumor - blood vessel hyperplasia due to *growth stimuli (classically pregnancy and trauma); often bleed profusely - surgically removed
Cherry Hemangioma
benign capillary proliferations common in middle-ages or elderly; classically on trunk - develop w/ aging; may bleed from trauma
Cystic Hygroma
congenital malformation in newborns; large cyst containing *lymph (obstruction of lymph drainage) - classically develops on the neck
often identified on prenatal ultrasound
increased risk of Trisomy 21 and Turner syndrome
Glomus Tumor
structure in the dermis of the skin (fingers and toes) - modified smooth muscle cells that function to regulate skin temperature (shunts blood awareness from surface in cold)
pink/purple papule or nodule that are PAINFUL esp when exposed to cold
Strawberry Hemangioma
benign hemangioma - excess proliferation of blood vessels - appear in newborns - typically a single lesions involute within a few years
Nevus Simplex
Stroke bite/ Salmon Patch “birthmark”
capillary malformation (not a tumor)
pink-red macule - fades in first few years of life
Nevus Flammeus
Port Wine Stain
malformation of dermal capillaries and venules - there is slow blood flow; causes pink/red patches often unilateral - blanch when press - do NOT regress (grows as child grows)
can have Sturge-Weber syndrome
Impetigo
superficial skin infection - neutrophils collect beneath the stratum corneum - leads to “honey-colored” crust lesion
HIGHLY CONTAGIOUS!
Strep aureus or Strep pyogenes
Bullous Impetigo
form of impetigo that forms a bulbous - seen in children and commonly involves the trunk - ALWAYS caused by Strep aureus (never Strep pyogenes)
Strep aureus Exfoliative Toxin cleaves *desmoglein 1 complex - affects the stratum granulosum - leads to bullous impetigo
Pathology of Bullous Impetigo formation
Caused by Strep aureus Exfoliative Toxin (exfolatin) cleaves *desmoglein 1 complex (desmosomes) - affects the stratum granulosum - leads to bullous impetigo
Scalded Skin Syndrome
newborn disease caused by the colonization of S. aureus - diffuse exfoliative toxin - sloughing off skin “Nikolsky’s sign” - skin slips off with gentle tug
heals completely with no scar
tx: antibiotics
Erysipelas
infection of the superficial dermis - occurs in young children and older adults - caused by Strep pyogenes
Acute onset - fever, chills, rash (clear demarcation of rash and normal skin)
Cellulitis
infection of deep dermis and subcutaneous fat; elderly - caused by Strep pyogenes and Strep aureus
Slow onset - focal pain, rash with warmth over days - spreading border
Skin abscess
collection of pus - walled off in dermis or subcutaneous space - complication of cellulitis or erysipelas
Necrotizing fasciitis
infection of fascia - involves muscle fascia and subcutaneous fat; skin goes through many color changes (red/purple/blue/gray/black); pain and tenderness may be “out of proportion to exam” minor rash with extreme tenderness - pt often mistake for muscle injury
often fulminant and deadly (uncontrolled spread) - requires urgent surgical debridement
crepitus can occur (crackling sound when skin is pressed)
Necrotizing Fasciitis type I
polymicrobial - often anaerobes (Bacteroides, Clostridium etc) and Strep or Staph - occurs in pts who have poor blood flow to skin such as diabetics, immunocompromised, vascular disease
Usually occurs following surgery
Necrotizing Fasciitis type I
occurs in healthy ppl after skin injury (fall) and caused by Strep pyogenes
watch for pain out of proportion (may also have fever and hypotension)
Pemphigus
Blisters
hallmark = acantholysis (loss of connection between keratinocytes); involves mucus membranes (mouth) and skin
pemphigus vulgaris
most common form of blistering
autoantibodies against desmoglein (component of desmosomes); disrupts connections in the stratum spinosum
large *flaccid bull that easily burst (not tense) - most rupture and scabbed; often presents first w/ oral bull and ulcerations (may present w/ painful chewing or swallowing)
(+) immunofluorescence for IgG in a “reticular” pattern like a net is a classic finding in which skin pathology?
pemphigus vulgaris - autoantibodies against desmoglein (component of desmosomes); disrupts connections in the stratum spinosum
with this finding there is increased mortality - infections and side effects to Rx
Bullous pemphigoid
looks like pemphigus
autoantibodies against *hemidesmosomes (epithelial cells to basement membranes); bull are subepidermal and nonacantholytic - biopsy will show eosinophils and lymphocytes - immunofluorescence shows a line at base of epidermis
elderly (80 yrs)
Dermatitis Herpetiformis
“herpes-like” skin condition associated w/ celiac disease; pruritic and classically on extensors: elbows and knees
IgA deposition in the dermal papillae
Celiacs: small bowel intraepithelial lymphocytosis, crypt hyperplasia and progressive villous atrophy
urticaria
“hives” type 1 hypersensitivity reaction caused by IgE-dependent mast cell degranulation leading to histamine release - there are no changes in the epidermis but dermal edema is present.
Atopic Dermatitis
Eczema - chronic disorder with flares and remission - a hypersensitivity; usually occurs in children and presents as red itchy rash on the skin
Increased serum IgE, family hx; occurs w/ allergic rhinitis and asthma
**Filaggrin -protein in stratum corneum (pts w/ this deficieny air at increased risk to develop eczema)
Contact Dermatitis
type IV hypersensitivity - localized area skin w/ contact to allergen
Common causes: poison ivy, Nickel (jewelry) and laundry detergents
Drug Rash
“non-immediate” reaction to drug days to weeks after starting drug - type IV hypersensitivity; often w/ some penicillin antibiotics
Steven-Johnson Syndrome
severe skin reaction; type IV hypersensitivity - usually triggered by drugs
Hallmark = necrosis of the epidermis
Nikolsky sign = skin slips off w/ simple tug
Typical presentation: prodrome 1-3 days before skin findings w/ fever and flu-like symptoms then lesions start on face/chest and spread symmetrically- red and tender skin, progresses to vesicles/bullae and then skin starts to slough off
pt presents w/ prodrome 1-3 days before skin findings w/ fever and flu-like symptoms then lesions start on face/chest and spread symmetrically- red and tender skin, progresses to vesicles/bullae and then skin starts to slough off
Steven-Johnson Syndrome; severe skin reaction; type IV hypersensitivity - usually triggered by drugs
Erythema multiform
skin disorder that is associated w/ infections; most common is Herpes simplex virus (children - mycoplasma pneumoniae); thought to be cell-mediated type IV autoimmune reactions
hallmark = “target lesion”
Actinic Keratosis
premalignant skin lesions caused by sun exposure - can lead to squamous cell carcinoma; round red/brown papules or plaques in sun exposed areas; biopsy - hyperkeratosis and epidermal cell dysplasia and parakeratosis (retained nuclei)
Squamous Cell Carcinoma
2nd most common skin cancer; occurs in sun exposed areas (damage by UV light); rarely metastasize to regional nodes (usually benign); occurs in older pts
red and scaling plaques with sharp border and more advances lesions can crust and bleed
hallmark = keratin pearls
Risk factors for Squamous Cell Carcinoma
Sun exposure
Chronic immunosuppression
Chronic skin inflammation
Arsenic exposure (contaminated water)
Keratoacanthoma
variant of SCC that is usually benign and self-resolving “dome-shaped” nodule with central hyperkeratosis
Classic feature = rapid growth (weeks) and then regression
Bowen’s Disease
squamous cell carcinoma in situ
well-demarcated scaly patch or plaque
Basal cell carcinoma
most common skin cancer; slow growing and has the LOWEST potential for recurrence or metastases; grows in sun-exposed areas “pearly” papules or nodules and may have telangiectasia
hallmark = nests of “basaloid” dark cells in dermis and also will see palisading nuclei
nests of “basaloid” dark cells in dermis
hallmark in Basal cell carcinoma
Superficial basal cell carcinoma
special variant of BCC; lesions are red to pink plaques with a slight scale; mostly occurs on trunk
Superficial basal cell carcinoma
special variant of BCC; lesions are red to pink plaques with a slight scale; mostly occurs on trunk
Melanoma
highly malignant skin cancer ABCDE
Lentigo maligna
type of melanoma that is confined to the epidermis (growing dark spot confined to the epidermis) - it is slow growing (takes years to develop); occurs in elderly
Neurofibromatosis
AD neurocutaneous disorder of nerve tumors with skin and eye findings; mut in NF1/von Recklinghausen disease (most common) - tumor suppressor gene on chr 17 - leads to RAS overactivity - uncontrolled growth
NF1/von Recklinghausen disease
the most common subtype of Neurofibromatosis; mut in NF1 (tumor suppressor gene) leads to RAS overactivity and uncontrolled growth; it is a nerve tumors with skin and eye (Lisch nodules) findings
Other features:
optic gliomas (by the age of 3yrs)
bone abnormalities
intellectual impairment
AD w/ 100% penetrance w/ *variable expressivity (variability in features)
Brown spots on the iris
Lisch nodules - as seen in NF1/von Recklinghausen disease - will also see skin lesions
Cafe-au-lait-spots “coffee with milk”
classic skin finding in NF1/von Recklinghausen disease - will also see eye involvement (Lisch nodules)
3 yr old to w/ an optic glioma
one of the potential manifestations of NF1/von Recklinghausen disease - will also see eye involvement (Lisch nodules) and skin lesions - Cafe-au-lait-spots “coffee with milk”
Neurofobromatosis 2
less common than NF1
AD NF2 mut - CNS tumors - *Bilateral schwannomas (acoustic neuromas - CN VIII); occurs in almost all pts
Tuberous Sclerosis
familial cancer syndrome
hallmark = (TSC1) hamartomas and (TCS2) seizures
mut in mTOR - overactivity - unregulated cell growth
look for “ash leaf spots” pale hypopigmented lesions or “shagreen patches” and CNS tumors
CNS tumors in Tuberous Sclerosis
cortical tubers (distorted cortex)
subependymal nodules (ependyma = lining of ventricles)
Subependymal giant cell astrocytomas - low grade astrocytomas that can obstruct ventricles and lead to hydrocephalus
Rhabdomyomas in Tuberous Sclerosis
benign tumors of muscle cells; classic feature in Tuberous Sclerosis (90%) - they are embedded in the ventricular wall and can cause obstruction or arrhythmias
Renal manifestations of Tuberous Sclerosis
Renal Angiomyolipomas is the most common; multiple or b/l growths of epithelioid cells around vessels that can cause *hemorrhage and pain; can lead to renin-dependent hypertension - risk of chronic kidney disease
Classic case: young child/infant who develops seizures. On PE you find “ash-leaf spots” and angiofibromas, what should you suspect and what is associated with this disorder?
Tuberous Sclerosis - hamartomas
Sturge-Weber Syndrome
vascular disorder of capillaries (not inherited) w/ 3 classic features:
1. port-wine stain on face (birthmark)
2. leptomeningeal angioma (brain tumor) *SAME SIDE as port-wine stain!
3. increased ocular pressure (glaucoma)
3 classic features:
1. port-wine stain on face (birthmark)
2. leptomeningeal angioma (brain tumor) - seizures
3. increased ocular pressure (glaucoma)
Sturge-Weber Syndrome
Sturge-Weber Syndrome Genetics
spontaneous GNAQ gene that occurs after fertilization (somatic mutation) and has features of mosaicism (some cells are normal/some mutated)
von Hippel-Lindau Disease
genetic cancer syndrome (benign and malignant tumors) requires “two hits”
VHL gene mut on chr 3 (tumor suppressor) causes *ubiquitination of hypoxia-inducible factor (HIF) - cells response as though they are hypoxic and leads to blood vessel growth
MULTIPLE hemangioblastomas (benign and well-circumscribed but can compress structures and hemorrhage) in CNS
phase of wound healing
keratinocytes are responsible for wound re-epithelization; they migrate into the wound from its edges and are repopulated by replication with the stratum basal; keratinocytes continue to migrate and proliferate until they contact other similar cells, a regulatory mechanism known as contact inhibition
ecthyma gangrenosum
ecthyma gangrenosum is a cutaneous necrotic disease w a strong association w Pseudomonas aeruginosa bacterimia; it occurs from perivascular invasion and release of tissue-destructive exotoxins, causing vascular destruction and insufficient blood flow to patches of skin that become edematous and subsequently necrose
