Lecture 67: Dermatopathology Response to Injury

What is thinning of skin due to decreased epidermal/dermal thickness caused by steroids, chronic ischemia, radiation, or autoimmune cytotoxicity?

atrophy

Smooth skin with loss of surface detail indicates what type of skin lesion?

atrophy

What type of skin lesion is common on pressure points?

callus

What is localized thickening (lichenification) from chronic pressure or friction?

callus

What is a dilated follicle filled with keratin and sebum that can rupture and cause inflammation?

comedone

What skin lesion is seen in chronic solar injury, endocrine disorders, or breed syndromes (Schnauzers)?

comedone

What is skin crusts?

dried serum, necrotic cells, or exudate on surface

What type of skin lesions are secondary lesions in infections such as dermatophilosis or pemphigus foliaceus?

crusts

What are fluid or keratin-filled sacs lined by epithelium?

cysts

What is a circular ring of exfoliating stratum corneum with erythematous margin?

collarette

What skin lesion is characteristic of staphylococcus pseudointermedius infection (superficial spreading pyoderma)?

collarette

What skin lesion is most, nonhemorrhagic, and involves partial-thickness epidermal loss?

erosions

What type of skin lesion common in self-trauma or mild injury heals without scarring?

erosions

What is full thickness epidermal loss exposing dermis, often hemorrhagic and granular?

ulcers

What is the fibrotic remodeling following injury? These can be atrophic (depressed) or hypertrophic (raised)?

scars

What type of skin lesion can cause permanent hair loss or pigmentation loss?

scars

What is the difference between vesicles and bullae?

vesicles < 1 cm and bullae > 1 cm

What type of fluid filled skin lesion is seen in viral, autoimmune, or hereditary blistering diseases?

vesicles/bullae

What are raised solid lesions caused by cellular infiltration or tissue deposition?

papules/nodules/plaques

What skin lesion commonly seen in pyoderma or pemphigus is elevated and filled with pus?

pustules

What is the dry or oily accumulation of keratin seen in seborrhea, ectoparasitism, lupus, or ichthyosis?

scale

What are the hard conical keratin projections associated with papillomas, SCC, or viral infections?

cutaneous horns

What is the thickened, folded skin from chronic trauma or inflammation common in chronic dermatitis?

lichenification

What skin lesion is characterized by white hair from melanocyte loss in follicles and commonly seen in vitiligo, alopecia areata, trauma, or aging?

leukotrichia

What is excess dermal hyaluronic acid deposition, causing thickened, pitted skin seen in Shar Pei dogs (genetic) or hypothyroidism?

mucinosis

What are the epidermal injury reaction patterns?

hyperplasia, hyperkeratosis, parakeratosis, dysplasia, necrosis, vesiculation

What are the skin inflammatory patterns:

perivascular/interstitial dermatitis, vasculitis, folliculitis, panniculitis

What are the two types of radiation injury?

1. ionizing radiation (x-rays): high-energy, causes DNA ionization and tissue necrosis

2. nonionizing radiation (UVR): damages DNA through chemical reactions, causing photoaging and neoplasia

What are the results of UVA and UVB solar injury?

sunburn, solar dermatitis, actinic keratosis, and squamous cell carcinoma affecting poorly pigmented or sparsely haired areas

What is the difference between UVA and UVB solar injury?

UVA: penetrates deeper, generates free radicals → DNA and membrane damage

UVB: directly damages DNA, forming pyrimidine dimers → apoptosis or mutation

What is chronic solar dermatitis?

result of prolonged UV exposure that leads to epidermal hyperplasia, hyperkeratosis, and comedone formation → ruptured actinic comedones can lead to pyogranulomatous dermatitis

What is moderate heat dermatitis?

dermatitis caused by chronic radiant head from pads, heaters, or surfaces → erythema, alopecia, hyperpigmentation

What are the four types of thermal burns?

1. first-degree: epidermal erythema, edema

2. second-degree: vesicle/blister formation

3. third-degree: full-thickness necrosis of dermis and adnexa

4. fourth-degree: extends to subcutis or muscle

What is acute solar injury (sunburn)?

acute UVB injury affecting nonpigmented, sparsely haired skin → keratinocyte necrosis, inflammation and pain → if chronic = hyperpigmentation, scaling, lichenification

What can chronic UV damage lead to?

actinic keratosis, squamous cell carcinoma, hemangiomas, and hemangiosarocmas

True or false: prognosis of UV-induced hemangiosarcomas is better than non-sun-induced types

true

What is the cold injury causing vascular ischemia and cellular dehydration, leading to pale necrotic skin on extremities and coagulative necrosis and thrombosis in microvasculature?

frostbite

What is type I - primary (phototoxic) photosensitivity?

ingestion of preformed photodynamic compounds in plants (ex. St. John’s wort, buckwheat) or drugs (tetracyclines, phenothiazine) causing lesions on white-haired, sun-exposed skin (commonly in herbivores)

What is type II - congenital (porphyric) photosensitivity?

defective porphyrin metabolism → accumulation of uroporphyrins and coproporphyrins (ex. bovine congenital porphyria) ; affects poorly pigmented areas, commonly seen in cattle, pigs, and cats

What is type III - secondary hepatogenic photosensitivity?

(most common type) liver unable to excrete phylloerythrin (chlorophyll breakdown product), triggered by lantana, tribulus, or mycotoxins and causes erythema, edema, blisters, and necrosis (facial eczema) in cattle and sheep

What is the pathophysiological pathway of photosensitivity?

Photodynamic compounds + sunlight (UVA/UVB) → reactive oxygen species → membrane and DNA damage → necrosis and inflammation in lightly pigmented skin

What can cause skin atrophy?

excess steroids (systemic or topical), chronic ischemia, and radiation injury

What is a morphologic characteristic and important clinical lesion of skin atrophy in dogs?

loss of cobblestone appearance of nasal planum (skin smoothing)

What skin lesion is present on this dog’s elbow?

callus

comedone

collarette

erosions

lichenification

cutaneous horn

This injury was a result of sustained pressure injury to the skin causing ischemic necrosis.

decubitus ulcer

What is affecting this sheep?

type III phototoxicity