Integumentary System

Derma

related to the skin

Dermatitis

Inflammation affecting the skin

• derma = skin

• itis = inflammation

Dermatology

The branch of medicine concerned with the diagnosis and treatment of skin disorders

Dermatopathology

Branch of pathology concerned with the study of skin disorders; pathology of the skin

What is the integument?

The skin, and the largest organ of the body. It has several functions including:

• physical barrier against external environment

• immunity and wound healing

• body temp regulation

• barrier to fluid loss

• synthesis of Vitamin D

• detection of stimuli

• pigmentation

What are the layers of the integument?

• epidermis

• dermis

• subcutis

Which layer of the integument supports and houses the majority of the structures?

the dermis

Describe the epidermis.

• outermost layer of skin

• composed of layers of epithelial cells

• cells produce keratin

Describe the dermis.

• middle layer of the skin

• supports the epidermis as well as structures like blood vessels

• composed of an extracellular matrix made of collagen

Describe the subcutis.

• deepest layer of skin

• insulates and cushions

• composed primarily of adipose tissue

What are adnexa?

Secondary structures of the integument.

• hair follicles

• sweat glands

What are some unique aspects of skin pathology?

• large surface area that contacts irritants, pollutants, trauma, and pathogens

• lesions are readily apparent

• large range of severity going from aesthetic to life threatening

• limited range of responses

What are exogenous factors in terms of the integument?

• factors from outside the skin

  • allergens, parasites, chemicals, physical injuries

What are endogenous factors in terms of the integument?

• factors from inside the body

  • immunologic, congenital, hereditary, hormonal

Since the skin can only respond in so many ways and many skin diseases have a similar appearance, how can we differentiate between conditions?

• histology

• ancillary testing (bacterial cultures)

• clinical history

Describe the epidermal thickening response to injury

• epidermal hyperplasia

• increased number of epithelial cells causes thickening

• can also result in increased keratin

Describe the dermal thickening response to injury.

• dermal fibrosis

• increased fibrous tissue (collagen)

• part of the normal healing process, but can sometimes be excessive

Describe hyperpigmentation

• a response to injury

• increased melanin pigment

• indicative of a chronic change

  • inflammation or trauma

Describe depigmentation

• a response to injury

• decreased melanin pigment

• injury to melanocytes

  • often autoimmune

  • ex. vitiligo

What causes cell death in the integument?

• solar injury

• thermal or chemical burns

• autoimmune disorders

• ischemia (loss of blood supply to an area)

Describe inflammation as a response to injury.

• infiltration of inflammatory cells into the skin

• location of inflammation:

  • dermatitis: skin

  • folliculitis: hair follicles

  • adenitis: glands

  • panniculitis: subcutis

  • vasculitis: blood vessels

• causes include infectious organisms, immune responses, or they can be idiopathic

What are primary lesions?

• direct result of the disease process

• the first lesion seen

What are secondary lesions?

• evolution of change to a primary lesion or the result of outside forces

  • scratching, chewing, etc.

• primary lesions can evolve into secondary lesions

• primary lesions can occur along secondary lesions

• sometimes only secondary lesions are present

Papule

• small raised firm area

• less than 1 cm

• can coalesce to form a plaque

Plaque

• elevated flat-topped lesion

• greater than 1 cm

Wheal

• smooth raised area

• aka: hives

• often seen with insect bites and allergies

Macule

• flat area of color change

• less than 1 cm

Crust

• dried fluid or exudates on skin surface

• “crusty”

• can be mixed with keratin, serum, blood, cellular debris, and inflammatory cells

Scale

• fragments of keratin on the skin surface

• flaky

• can be dry or oily

Lichenification

• thickened skin

  • accentuated with lines and folds

• often accompanied by hyperpigmentation and hair loss

Collarette

• flat ring of scale

  • expands peripherally

  • central areas can become hyperpigmented

• the ring in ringworm

Excoriation

• superficial scratch in the epidermis

• due to physical trauma such as itching and scratching

Fissure

• deep, vertical oriented cleft/crack

• extends from epidermis into dermis

Comedo

• plugged hair follicle (plugged with keratin or sebum)

• aka: blackheads

Cyst

• cavity lined by epithelium and filled with material

  • liquid or semisolid material

• can rupture and cause inflammation

Pustule

• raised superficial accumulation of pus

• caused by bacterial infection (pyoderma) or autoimmune disorders (pemphigus foliaceus)

Vesicle/Bulla

• elevated, fluid filled cavity

• aka: blisters

• vesicles < 1 cm

• bulla > 1 cm

Erosion

• partial thickness loss of epithelium, moist and glistening

• can be due to rupture of vesicles

• does not extend into dermis

Ulcer

• full thickness loss of epithelium

• extends into dermis through the epidermis

• deeper version of erosion

Nodule

• elevated, firm, distinct growth

• needs histology

Neoplasm

• abnormal mass of tissue, uncoordinated in growth

• cancer

• need histology

What is one way we differentiate between lesion?

biopsy: removal of a piece of tissue to be examined in a lab

What is an incisional biopsy?

removal of part of the lesion

What is an excisional biopsy?

removal of the entire lesion

What does a biopsy allow a pathologist to do?

• allows examination of structural changes in all of the layers of the skin and associated structures

• detect present of neoplasia, inflammatory cells, and infectious agenets

Ectoparasites

• external parasites

• most are of the phylum Arthropoda (arthropods)

• live in the superficial layers of the skin or hair follicles

Describe fleas

• an ectoparasite insect

• ctenocephalides felis

• laterally compressed

• no wings

• feed on blood

• only adult fleas are on the host

• can persist in the environment for months due to hardy pupae

Describe the effects of a flea infestation

• due to a high number of fleas

• can affect any animal

• can be life threatening

  • anemia in young, old, or malnourished animals

• can spread other diseases like plague, tapeworms, or cat scratch disease

• must treat the environment and fleas on the animal

Describe flea allergies

• hypersensitivity to salivary antigens of the flea

• only takes a low number of fleas to cause issues due to the hypersensitivity

• lesions that can occur are:

  • papules

  • lichenification

  • alopecia

• lesions often occur on the back and at the base of the tail

• very itchy for the animal (pruritus), often resulting in self-trauma lesions

Describe biting lice

• an ectoparasite

• biting lice - mallophaga

• feed on cellular debris

• have a wide head

Describe sucking lice

• an ectoparasite

• sucking lice - anoplura

• feed on blood

• narrow head

Describe lice

• there are biting and sucking varities

• dorsoventrally compressed

• entire life cycle is on the host

• eggs are attached to hair, and are called nits

Describe the effects of lice infestations

• associated with:

  • colder months

  • poor husbandry

• few primary lesions, but there are secondary lesions due to scratching

• can spread diseases like swine pox

Describe scabies

• endoparasite arachnid mites

• sarcoptes scabei can affect most mammals, including humans

• tunnel through the epidermis

• transmitted by direct contact

  • highly contagious

  • can spread quickly through a herd

What is sarcoptic mange?

• an infestation with the ectoparasite sarcoptes scabei

• starts in areas with less hair like around the eyes and nose

• lesions include alopecia, lichenification, hyperpigmentation, crusts, and scales

• VERY ITCHY

Describe demodex

• ectoparasite arachnids

• different species in dogs and cats

• cigar shaped

• live in hair follicles

• noncontagious

• part of the normal fauna of the skin

  • lesions occur with disruptions of host-parasite equilibrium, leading to over-proliferation of the parasite

    • allergies, systemic disease, immune suppresion

Describe demodicosis/demodectic mange

• localized demodicosis

  • often juvenile onset that self-cures within 12-18 months

  • lesions around eyes, face, and front legs

• generalized demodicosis

  • juvenile or adult onset

  • genetic predisposition

  • more severe

  • whole body lesions

Describe bacteria as an agent of skin infection

• primary infection: when the bacteria causes the clinical disease

• secondary infection: when the bacteria causes infection after damage is already done to the skin

• common cause of many infections is the Staphylococcus bacteria

Describe superficial pustular pyoderma

• aka impetigo

• caused by S. pseudintermedius

• in cows, ewes, does, puppy pyoderma

• lesions are pustules in the epidermis

Describe porcine exudative dermatitis

• aka greasy pig disease

• caused by S. hyicus

• affects neonatal pigs and is often fatal

• clincial signs:

  • greasy appearance

  • brownish exudate around eyes, ears, snout

• bacterial toxins disrupt cell-cell adhesion, causing exudation of fluids and impaired defense barrier

Describe diamond skin disease

• skin infection in pigs caused by E. rhusiopathie

• bacteria enter the bloodstream, causing localized vasculitis, resulting in the formation of blood clots and infarction

• infarction: necrosis from blocked blood supply

• rhomboidal areas of necrosis are the main distinguishing lesions

Describe dermatophilosis

• aka rain rot

• caused by D. congolensis

• in cattle, horses, and sheep

• caused by wet weather conditions that favor the bacteria

• lesions include papules and thick crusts

• the bacteria are filamentous

Describe fungal infections

• mycotic infections are those caused by fungal organisms

• types

  • superficial: surface of epidermis

  • cutaneous: within layers of epidermis

  • subcutaneous: involve layers of the dermis and subcutis

  • systemic: spread throughout the body

Describe dermatophytosis

• aka ringworm

• in cats, dogs, horses, etc

• cutaneous mycosis

• very contagious

• colonies in keratinized structures like the hair, outer epidermis, and claws

• lesions are circular scaly or crusty patches of alopecia with a peripheral red ring

Describe pythiosis

• aka swamp cancer

• caused by Pythium insidisum, a fungus like water mold

• in horses, cattle, and dogs

• subcutaneous mycosis

• predisposing factors include contamination of skin wounds and interaction with warm, standing water

• lesions include deep dermal and subcutaneous nodules

  • kunkers are seen in horses - yellow friable fragments of necrotic tissue

• rapidly progressive and often fatal in dogs

What are the main viruses we focus on?

Many of the viruses affecting skin are DNA viruses

the big ones are poxviruses, papillomaviruses, and herpesviruses

Describe poxvirus

• variety of poxviruses affecting many different species

• lesions include macules → papules

• most serious conditions:

  • sheeppox: a systemic disease with hemorrhagic macules and lesions in the lungs, kidneys, and GI tract

  • orf (contagious ecthyma): primarily affects young sheep and goats, causing papules, plaques, and crusts on the lips; it is also zoonotic

Describe papillomavirus

• species and tissue specific

• viral papilloma

  • warts

  • benign neoplasms

  • epidermal proliferation

  • frondlink extensions of epithelium extending from the epidermis

  • often seen on the face or muzzle

  • may spontaneously regress

Describe equine sarcoid

• a disease of horses caused by Bovine papillomavirus

• most common skin tumor in horses

• lesions:

  • benign dermal tumors

  • proliferation of fibroblasts

  • abundant collagen

• behavior: locally invasive and does not metastasize

What is neoplasia?

• “new growth”

• abnormal or excessive growth of tissue

• can be benign or malignant

• can affect all layers of the skin

Describe carcinoma

• a type of neoplasia affecting epithelial cells like the skin and glands

Describe sarcoma

• spindle cells, a neoplasia affecting bone, cartilage, and endothelium

Describe round cell tumors

• neoplasia of round cells (inflammatory cells)

Describe squamous cell carcinoma

• malignant neoplasm of epidermal cells in cats, dogs, and horses

• predisposing factors:

  • solar damage

  • lack of pigment (white cats)

  • sparse haircoats (tips of ears)

• proliferating lesions extending from the epidermis are often ulcerated

• very locally aggressive

Describe soft tissue sarcoma

• malignant neoplasm of spindle cells

• in dogs and cats

• group of closely related tumors

• lesions include tumors in the subcutis that are fibrous

Describe mast cell tumors

• malignant neoplasm of round cells

• in dogs, cats, horses, cattle, pigs (most common diagnosed skin cancer in dogs)

• can be cutaneous or subcutaneous

• lesions are variable in appearance, but are often solitary, raised, and hairless

• mast cells: prominent granules often accompanied by eosinophils

What are other causes of skin disease besides infectious agents and neoplasia?

• immune mediated issues like allergies or autoimmune disorders

• nutritional deficiencies

• endocrine disorders: hypothyroidism, hyperadrenocorticism (Cushing’s), hyperestrogenism

Describe allergies

• causes:

  • atopy - environmental agents

  • flea bites

  • contact dermatitis

  • food allergies

• can have similar appearances to other skin issues

• lesions:

  • reddened

  • pruritic (itchy)

  • secondary lesions from self trauma

  • chronic - hyperpigmentation and lichenification

• secondary bacterial or yeast infections

Describe autoimmune disorders

• ex. lupus, pemphigus, bullous pemphigoid

• immune system improperly targets normal cells or molecules

• often occur at dermal-epidermal interface

  • can result in the separation of layers

Describe endocrine disorders of the skin

• common in dogs

• lesions

  • bilaterally symmetrical alopecia

  • non-pruritic

Describe hypothyroidism in terms of skin disorder

• most common endocrine disorder in dogs

• decreased thyroid hormone

Describe hyperadrenocorticism in terms of skin disorder

• aka Cushing’s disease

• excessive glucocorticoids

• thinned epidermis

• calcinosis cutis - mineralization of dermal collagen