Patho E2: Derm

What are the functions of the skin?

• maintains normal body temp

• provides a protective barrier

• receives external sensory stimuli

• controls insensible water loss

Which layer of the skin is superficial, tough, stratified, has 5 layers, and contains melanocytes?

epidermis

Which layer of the skin is semi-fluid, binds the body together, and contains nerve endings, sweat/oil glands, hair follicles, and blood vessels?

Dermis

What are the 5 layers of the epidermis? (out→in)

corneum, lucidum, granulosum, spinosum, basal

Which layer of the epidermis scales?

corneum

What are melanocytes?

dendritic; synthesize melanin, provide protection from UV, basal layer

What are Langerhans cells?

dendritic; bone marrow derived antigen presenting cells

What are the three types of skin diseases?

inflammatory, infectious, neoplastic

Macule:

• area of increased/decreased pigmentation

• NO elevation or depression

• <1 cm

• not palpable

• superficial layers only

Patch:

• macular type lesion

• circumscribed

• > 1cm in diameter

Papule:

• superficial, solid lesion

• < 1cm

• often in clusters

• can accompany rashes

What causes papules?

inflammation, accumulated secretions, infection (disseminated histoplasmosis), acne, hypertrophy of skin cells

Plaque:

• plateau-like elevation

• SA > height

• can form by confluence of papules

• > 1cm in size

What causes plaque?

pruritic disorders (eczema, dermatitis) and Lichenification

What is Lichenification?

surface is rough and thickened; skin lines become accentuated → resembles tree bark

Vesicle:

• small fluid filled lesion on/below skin

• Circular lesions

• < 1cm in diameter

Bulla:

• circumscribed collection of free fluid

• > 1cm

Pustule:

• vesicle/bulla containing purulent fluid

• superficial skin cavity containing purulent exudate

  • can be different colors

Blister:

• defines both vesicles and bulla

• defense mechanism

  • epidermis separate from dermis

  • fluid collects between the layers

What can cause a blister?

chemical/allergic rx, physical injury (heat, frost, friction)

Nodule:

• solid, circular lesion

• > 1cm

• usually invades epidermis and lower dermis

Wheal:

• “urticarial exanthema urticaria”

• rounded, or flat topped, edematous plaque

• well demarcated

• no scaling

• no epidermal involvement

• Shape: round, oval, gyrate, annular or serpiginous

What causes wheals?

allergic response; can be reproduced by Darier’s sign

What is Darier’s sign?

gentle rubbing of the lesion → local itching, erythema and wheal formation within 5 minutes

What is dermatographism?

“writing on the skin”; common localized hive reaction

Cyst:

• encapsulated lesion filled with fluid or semisolid material

• elevated, circumscribed, palpable

• enclosed sac w/ distinct membrane lining

Abscess:

• collection of pus

Crusts:

• dried serum or exudates on skin surface

• present after blisters rupture

• Blood → brown

• Serum → honey colored

• Pus → green/ yellow

Scales (desquamation):

• abn areas of stratum corneum

• inc rate of epidermal cell proliferation

• may be adherent or loose

  • large sheets or tiny particles

Erosion:

• skin defect with loss of epidermis only

• heals w/o a scar

Ulcer:

• skin defect with loss of epidermis & upper layer of dermis

  • can extend to lower layers

• always heals w/ scar tissue

Telangiectasias:

• small, enlarged blood vessels near the skin surface

• usually mms in size

• nose, cheeks, chin

Petechiae:

• small red or purple spot on the body

• often multiple at once

• < 3 mm

What causes petechiae?

minor hemorrhage, broken capillary, thrombocytopenia, dec plt function

Purpura:

• larger red or purple discolorations on the skin

• 3 mm - 10 mm

• “bruise”

What causes purpura?

bleeding under the skin

Ecchymosis:

• capillary damage allows blood to extravasate into surrounding tissues

• > 1cm diameter

What causes ecchymosis?

usually blunt trauma

What can help dx petechiae, purpura, and ecchymosis?

they do NOT blanch w/ pressure

Tumor:

• solid lesion w/ elevation & depth

• usually involves epidermis & dermis

• > 2 cm in diameter

• ± pigmentation

What type of lesion would you see if a pt had hookworm?

serpiginous lesion

How many patterns of dermatitis are there?

9

Perivascular dermatitis

• perivascular inflammatory infiltrate w/o sig epidermal involvement

• Ex: hives

Spongiotic dermatitis:

• associated w/ intracellular epidermal edema (spongiosis)

• Ex: allergic contact dermatitis

Psoriasiform dermatitis:

• associated w/ epidermal thickening from elongated rete ridges

• Ex: psoriasis

Interface dermatitis:

• cytotoxic rxn that affects the dermis and epidermis

• characterized by vacuoles and lymphocyte infiltrates

• Ex: lichen planus, Erythema Multiforme

Vesiculobullous dermatitis:

• Intradermal or sub epidermal cleavage

• Ex: bullous pemphigoid

Vasculitis:

• damage to cutaneous vessel walls

• Ex: leukocytoclastic vasculitis

Folliculitits:

• Rxn directed against colliculo-sebacous units

• Ex: acne folliculitis

Nodular dermatitis:

• nodular or diffuse dermal infiltrate w/o significant epidermal changes

• Ex: cutaneous sarcoidosis

Panniculitis:

• Involves the SC fat

• Ex: erythema nodosum

• common, chronic, relapsing, scaling condition

• sharply marginated and erythematous and surmounted by silvery scales

• most common onset age is third decade

• multifactorial, infx, injury, inherited, FHx

• thicker, rete ridges, “squirting dermal papillae”, only epidermis, nail beds → dystrophic nails, mucosal surfaces spared

Psoriasis

• extracutaneous manifestation of psoriasis

• deforming, asymmetric, oligoarticular arthritis

• distal interphalangeal joints of fingers and toes typically affected

• seronegative spondyloarthropathy

Psoriatic Arthritis

What are the two types of interface dermatitis?

Lichen Planus (chronic)

Erythema Multiforme (acute)

What is the pathophysiology of interface dermatitis?

• junction between papillary dermis and epidermis is obscured (basement membrane zone)

• T cells attack the basal keratinocytes producing vacuoles → necrosis of keratinocytes

• vacuolization, vacuolopathy, liquefaction degeneration

• develops in adulthood

• women > men

• lesions composed of CD8 cells, colloid bodies

• Etio: unk, drugs

• PE: pruritic polygonal purple papules, flat topped, bilateral/symmetric lesions, Wickham’s striae

• Common sites: genital skin, mucous membranes, flexor surfaces of the extremities

Lichen Planus

• uncommon

• men = women (2nd-4th decade)

• infiltrate composed of CD4 & CD8

• Etio: HSV infx, Rxn to meds, idiopathic

• PE: brief, self limited, crops on aural surfaces (distal portions of limb), can be life threatening, monomorphous pattern, expands from the center, target-like

Erythema Multiforme

scattered lesions or with limited mucosal involvement

EM minor

• prominent involvement in at least 2 or 3 mucosal site (oral, anogenital, conjunctival)

• severe, widespread cutaneous involvement

• includes Stevens-Johnson & toxic epidermal necrolysis (necrotic w/ 2^o vesiculation)

• tx like severe burn

EM major

• large tense blisters, inflammation, erythematous, pruritus, mucous membrane lesions

• extremities and lower trunk

• detachment of epidermis (lamina lucida) from dermis due to inflammation

• elderly, men = female

• Ig & complement deposited in basement membrane

• form of autoimmune disease

Bullous Pemphigoid

more severe form of pemphigoid

Pemphigus

• inflammatory disorder affecting small blood vesicles → palpable purpura (can also be vesicopustules, necrotic papules, ulcers)

• lesions appear in crops

• mainly lower extremities

• any age, M = F

• often following Strep/Staph infx, Drug rxn (PCN, thiazide diuretics, NSAIDS)

• systemic vasculitis s/ athralgias, malaise, myalgia

Leukocytoclastic Vasculitis

• eruption, pruritic rash due to Type 4 (delayed) immune rxn

• 24-48 hrs to develop

• 1st exposure may not yield rxn → sensitized pt

• Acute: erythematous papules, vesicles, bullae

  • blisters break → weeping & yellow crust

• variable perivascular inflammation

• infiltrate composed of lymphocytes and eosinophils

• causes: rhus dermatitis (poison ivy/oak), nickel, soaps, detergents

Allergic Contact Dermatitis

• most common form of panniculitis

• present in anterior lower extremities

• SC fat inflammation and necrosis: septal vs lobular

• numerous tender, deep red/brown lesions, demarcation difficult due to depth of origin

• infiltrate: lymphocytes, histiocytes, foamy macrophages

• women > men

• End result of inflammation (infxn, meds, hormones, IBD) persist as long as stimulus is present; sign of sarcoidosis

Erythema Nodosum

• hugely varied Sx: mild, asymptomatic → life treating lung disease

• often present on face

• young adults & AA >

• Mycobacterium (M. Tuberculosis), Histoplasma, virus

• Granulomas are present in dermis: non-caseating, w/o central coagulation necrosis

• CD4 direct immune response, CD8 limit extent of response

• Dx of exclusion, r/o everything else first

• lupus pernio (nasal rim), Lofgren’s syndrome (hilar LAD, uveitis, fever, arthralgia)

Cutaneous Sarcoidosis

• teenagers, some neonates and adults

• follicle-based comedones, inflammatory papules/pustules

• nodulocystic scarring acne caused by weak androgens = doesn’t occur before puberty

• open comedones: blackhead, orifice is open

• closed comedones: normal orific, follicle plugged below surface

• can be component of a syndrome: Stein-Leventhal (PCOS) or SAPHO syndrome

Acne

What are the 4 components to develop acne lesions?

• folliculosebaceous unit is plugged by keratin

• sebum production

• overgrowth of cutibacterium

• secondary inflammatory process

What do comedones transform into?

• inflamed papule

• pustule

• nodule of acne

What acne classification is characterized by few to several papules/ pustules (<10) and no nodules?

mild acne

What acne classification is characterized by several to many papules/ pustules (10-40) along w/ comedones (10-40) and few to several nodules?

moderate acne

What acne classification is characterized by numerous or extensive papules/pustules and many nodules?

severe acne

What causes follicular plugging?

keratinocytes become sticky and fail to slough

What causes bacterial overgrowth? (acne)

inc sebum within the follicle acts as a food source for C. acnes

What causes expansion of follicular canal?

sebum degrades to lipids and free fatty acids

What causes pustule formation?

C. acnes recruits neutrophils

What causes inflammation in acne?

neutrophilic enzymes weaken the follicle wall → rupture → release large amounts of inflammatory reactants into skin