Dermatology 1 Flashcards
skin layers, thickness in different areas
Complex structure made up of the epidermis, dermis and subcutaneous layers
Thickness:
o haired skin: 0.1-0.5 mm thick
o footpad and nasal planum: up to 1.5 mm
what proportion of cells in the epidermis are keratinocytes? what other cells are presnt?
Keratinocytes comprise 85% of the cells of the
epidermis
The balance is primarily composed of melanocytes.
Langerhans cells and Merkel cells
layers of the epidermis
Multiple cell layers that vary in shape, size, function, contents and polarity based on their location in the epidermis
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Cell layers:
o Stratum corneum – horny cell layer
o Stratum lucidum; footpad and nasal planum only
o Stratum granulosum – granular layer
o Stratum spinosum – prickle cell layer
o Stratum basale – basal cell layer
how are the cells of the epidermis held together?
The cells of the epidermis need to be held together for stability
> The major cell adhesion molecules of the cells of the epithelial tissues are known as desmosome
Desmosomes are made of 3 major families:
o Desmosomal cadherins
> E.g. desmogleins and desmocollins, important in pathogenesis of pemphigus, for example
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o Plakins
> E.g. desmoplakin
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o Armadillo proteins
> E.g. plakoglobin and plakophilin
what are hemidesmosomes? what can defects in hemidesmosomes result in?
Hemidesmosomes are important for epidermal – dermal adhesion; keeping the epidermis attached to the dermis. Defects in hemidesmosomes can result in subepidermal blistering diseases
stratum corneum
- what are the cells suspended in? where is this material made?
- structure and function? important in what disease process?
- The cells of the stratum corneum are suspended in lipids comprised of non-polar lipids, ceramides (the largest and most important group), free fatty acids and cholesterol
- Lamellar bodies are synthesized in the stratum spinosum. They contain precursors of the aforementioned lipids that fuse with the plasma membrane and secrete their contents into the intercellular space.
- The lipids undergo hydrolysis and enzymatic conversion. The structure appearance is often referred to as bricks and mortar.
- The “mortar serves very important functions and is critical in epidermal barrier function (of significant importance in allergic dermatitis pathophysiology.
dogs and cats have what type of hair follicles?
- structure?
Dogs and cats have a compound hair follicle arrangement
Usually, a cluster consists of 2-5 large primary (guard) hairs surrounded by groups of smaller secondary hairs (SHF, wool or down hairs, undercoat)
One of the primary hairs is the largest (cPHF) and it is flanked by several smaller lateral primary hairs (lPHF)
Each primary hair has an arrector pili muscle and is associated with sebaceous and sweat glands
The primary hairs emerge independently through a separate pore and may be surrounded by 5 - 20 secondary hairs
The secondary hairs emerge through a common pore
sebaceous glands - where are they found? purpose of secretion?
Distributed in the haired skin
Not found in the footpad or the nasal planum
Empty their oily secretion (sebum) into the hair canal which helps keep the skin pliable, provides skin and hair protection, is part of a chemical barrier against pathogens
Epitrichial sweat glands - where are they?
Distributed throughout the haired skin
Not in footpads or nasal planum
Also open into the hair canal
Atrichial Sweat Glands - where are they?
Found only in the footpads
important aspects of history to evaluate when seeking to make a dermatological diagnosis
- Hereditary predispositions
- Age of Onset
- How has the disease progressed with time?
- Severity and Duration
- Contagion
- Response to Therapy
- Affected areas
- Environment/housing/management
- Other, non-dermatological clinical signs?
Early age of onset diseases
- puppy bacterial infections (impetigo)
- parasites (Sarcoptes, Cheyletiella, Fleas,
Otodectes, Demodicosis) - fungal (dermatophytosis)
- juvenile cellulitis in dogs
- hereditary disease (ichthyosis and idiopathic seborrhea - genetically inherited scaling skin conditions)
- colour mutant alopecia and follicular dysplasia (associated with hairs that are easily fractured, leading to a scaling skin problem and hair loss over time)
- and even severe blistering diseases (rare) such as junctional epidermolysis bullosa
middle aged to older pet diseases
Most pets with environmental allergies start to exhibit clinical signs between 6 months and 3 to 5 years of life (May be later if the patient has moved to different geological regions later in life)
Immune mediated diseases
Endocrine diseases
what types of diseases should we consider for older pets?
o Neoplasia needs to be considered
o Adverse food reactions can occur at any age
o Parasites have no age predisposition and adult onset demodicosis may be an indicator of a more
serious underlying condition leading to immunosuppression
For itchy pets: what should we consider if the itchiness started at:
- less than 6 months of age
- more than 6 months of age but less than 3 to 5 years
- more than 5 years
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- what age for food reactions?
o less than 6 months of age, one should consider food intolerance and parasitic hypersensitivity as likely offenders
o more than 6 months of age but less than 3 to 5 years, one may want to add environmental hypersensitivity to the list as well as the above
o more than 5 years, environmental allergies would be less common (as long the patient has lived in the same region all their life).One may wish to consider pruritus secondary to infection, infestation, tumors (some forms of epitheliotropic lymphoma are pruritic) or immune mediated diseases as the more likely candidates in the older dog
o Food reactions are less time sensitive and can occur at any age.
itchiness usually preceeds lesions for what type of skin disease?
allergic skin disease
what things are less likely to cause seasonal pruritis?
- Adverse food reactions and parasitic hypersensitivities (other than fleas) are unlikely causes of seasonal pruritus unless a particular diet is fed seasonally.
- However, the greatest percentage of
environmental allergies are non-seasonal
Chronic non-lesional pruritus would be more commonly associated with:
allergic skin disease
Chronic deep oozing wounds is more suspicious for
infectious causes (although some deep sterile
diseases do occur – diagnosed by ruling out infectious causes)
how long should pyodermas be treated for? why?
usually 1-2 weeks past complete resolution as the surface of the skin heals faster than the deeper tissues
Patients with environmental sensitivities are more commonly itchy where?
- front end
parasites generally make an animal itchy at what end?
Parasites often prefer the hind end
Where do food allergies often cause itch?
- Food allergies can present anywhere but ears, paws and abdomen are frequently affected in dogs
- and head/face and neck are often affected in the cat in addition to the abdomen and ears.
- In one paper, 26% of patients with food allergies presented with otitis as the principal presenting sign.
Atopic animals most often present with involvement in what areas
pinnal, facial and pedal involvement
where do fleas like to live on the body?
Fleas like to be in the “Florida” or “Texas” triangle (named according to where you live) - the triangle
formed by the centre of the back at the thoracolumbar junction, moving laterally and distally towards the tail
Bilaterally symmetrical hair loss is more commonly associated with:
endocrine disease. But don’t be fooled, itchy pets can pull their hair out in a bilaterally symmetrical pattern
A “rat-tail” appearance is typical of:
hormonal disease
Concave pinnal erythema with normal ear canals is suggestive (but not diagnostic) of:
an allergy
Palmoplantar dermatitis and caudal metacarpal alopecia is a classical finding in:
allergic pets
Typical sites for scabies infestation include:
- the pinnal margins, elbows, hocks and the ventrum. - But don’t be fooled. I have diagnosed scabies in patients presenting with only ventral abdominal pruritus.
