Acute Dermatoses Flashcards
What are the projections between the dermis and epidermis called?
Dermal papillae
- interact with the epidermal ridges to strengthen adhesion of the dermis and epidermis to each other
What are the epidermal derivatives
Nails
Hairs
Sebaceous and sweat glands
Cells of the epidermis
Stratified keratinized epithelium
Keratinocytes (most abundant)
Melanocytes
Langerhans cells
Tactile Merkel cells
Thick vs thin skin
Based on the density of epidermis
Thick = 400-1400 um
Thin = 75-150 um
Layers of the epidermis
Stratum basale
- single layer of basophilic cuboidal or columnar cells at the dermal-epidermal junction
Stratum spinousum
- thickest layer in thin skin with polyhedral cells that also has active synthesizing keratins
Stratum granulosum
- 3-5 layers of flattened cells that undergoes terminal differentiation of keratinization
- cytoplasm is filled with basophilic masses called “keratohyaline granules”
Stratum lucidium
- ONLY found in thick skin
- consists of a thin, translucent layer of flattened eosinophilic keratinocytes held together by desmosomes
Stratum corneum
- consists of 15-20 layers of squamous keratinized cells with Briefringent filamentous keratins
- is the thickest layer in thick skin
Eumelanins
Brown/black pigments that are produced by melanocytes
What is the primary step in melanin synthesis?
Tyrosine -> (3,4) dihydroxyphenylalanine (DOPA)
- done via tyrosinase activity
DOPA is then further transformed into melanin**
What are melanosomes?
Matrix structural proteins that accumulate in vesicles and form elliptical granules
- are about 1um long
The melanosomes get phagocytosed into keratinocytes and accumulate within.
ultimately protect DNA of the living keratinocytes from UV damage and ionizing radiation
Langerhan cells
Antigen presenting cells that are derived form monocytes.
- usually seen in the spinous layer and derived from monocytes
They are the professional antigen presenting cells of the skin
Lichenification
Thickened rough skin that is usually a result of repeated rubbing
Macules
Circumscribed flat lesions distinguished from surrounding skin by color
- are less than 5mm in diameter (if larger = nodules)
Plaques
Elevated flat-topped lesions that are usually >5mm in diameter
Wheal
Itchy transient and elevated lesions with variable blanching and erythema formed as a result of dermal edema
Acanthosis, hyperkeratosis and papillomatosis
Acanthosis = diffuse epidermal hyperplasia
Hyperkeratosis = thickening of the stratum corneum. Usually shows qualitative hyperplasia of keratin also
Papillomatosis = surface elevation caused by hyperplasia and enlargement of contiguous dermal papillae
Parakeratosis
Retension of nuclei in the striations corneum of the squamous epithelium
- this is normal on mucous membranes, but pathological on non-mucous membranes
Spongiosis
Intercellular edema of the epidermis
Acute inflammatory dermatoses
Are acute lesions (days-3 weeks) in duration and are characterized by inflammation, edema and epidermal vascular/subcutaneous injuries
**Are often marked by infiltrates consisting of mononuclear cells rather than neutrophils
Urticaria (hives)
Common disorder that leads to dermal microvascular hyperpermeability due to localized mast cell degranulation
Produces wheal plaques that are edamatous and pruritic
Stems from an immediate type 1 hypersensitivity reaction. Mast cells bind to IgE antibodies which are bound to viruses, pollens, foods, drugs, insect venom, etc.
- can also induce IgE-independent urticaria which is caused by opiates an antibiotics
Treatment of urticaria
Most respond to antihistamines
- refractory cases = immunosuprrants and MABs
Acute eczematous dermatitis
Eczema
Pruritic lesions that are often erythematous and ooze/become crusted
- chronically = raised, scaling plaques
Multiple subtypes
1) allergic contact dermatitis = topical exposure and delayed hypersensitivity
2) atopic dermatitis = defects in the keratinocytes Barrier function defined as skin with increased permeability to substances
* *highly genetic based**
3) drug-related eczematous dermatitis = hypersensitivity to a drug
4) photoeczematous dermatitis = abnormal reaction IV or visible light
5) primary irritant dermatitis = results from exposure to substances that chemically, physically or mechanically damage the skin
Allergic contact dermatitis
Triggered by exposure to environmental contact-sensitizing agents
- poison ivy is the classic example
1st exposure = reacts with self-proteins and creates neoantigens that can be recognized by T-cell adaptive immune system
- these neoantigens are processed by epidermal langerhan cells and migrate to draining lymph nodes to present to naive T-cells
2nd exposure = Re-exposure causes activation of memory CD4+ T-lymphocytes and migrates to affected skin sites during course of normal circulation, where they release cytokines and recruits additional inflammatory cells
type-4 delayed Hypersensitivity reaction
What other dermatological condition is always present in acute eczematous dermatitis?
Spongiosis (epidermal edema)
- shows superfical perivascular lymphocytic infiltrate
hence why it is sometimes synonymously called spongiotic dermatitis
Genetic component to atopic dermatitis
Concordant in 80% of identical twins and 20% in fraternal twins
**often is worse in childhood and gets better in adulthood
What is the atopic triad
Asthma, allergic rhinitis and atopic dermatitis
- these three often show up altogether
Erythema multiforme
Epithelial injury that is mediated by CD8+-Tcells
Uncommon and is often self-limiting
- is a hypersensitivity response to infections and drugs
Infections associated with erythema multiforme
Herpes simplex
Mycoplasma
Fungi species
**Less dangerous
Drugs associated with erythema multiforme
Sulfonamides, penicillin, salicylates, anti-malaria drugs
**More dangerous and high risk of SJS and TEN
Stevens-Johnson syndrome
Is a systemic, febrile form of erythema multiforme
- by itself not overly dangerous but makes patients prone to secondary infections which can lead to life-threatening sepsis
Toxic epidermis necrolysis (TEN)
Variant of erythema multiforme that is characterized by diffuse necrosis and sloughing of the cutaneous and mucosal epithelial surfaces
Looks very similar to extensive burn victims
