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Department of Pathology, Faculty of Veterinary Pathology, Zagazig University, Egypt.

Pathology of Skin BY Prof. Dr. Mohamed Hamed Mohamed +201224067373



I-Skin (cutis)

A. Epidermis 1. Horny layer (stratum corneum) 2. Clear layer (stratum lucidum) 3. Granular layer (stratum granulosum) 4. Prickle layer (stratum spinosum) 5. Basal layer (stratum basale)

B. Epidermal appendages (adnexa) 1. Glands of the skin

a. Sebaceous glands b. Apocrine sweat glands c. Exocrine sweat glands 2. Claw (ungues) 3. Hair (pili)

C. Dermis (corium) II-Hypodermis (subcutis)

GENERAL FUNCTIONS OF THE SKIN 1-Enclosing barrier: It is to make possible an internal environment for all other organs by maintaining an effective barrier to the loss of water, electrolytes and macromolecules.

2-Environmental protection: It provides protection from external injurious agents (chemical, physical and microbiological) from entrance into the internal environment.

3-Temperature regulation: Skin plays a role in the regulation of body temperature through its support of the hair coat and through regulation of the cutaneous blood supply.

4-Sensory perception: Skin is a prime sense organ for touch, temperature, pain and itch.

5-Motion and shape: The flexibility, elasticity and toughness of the skin allow motion and provide shape and form.

6-Antimicrobial action: The skin surface has antibacterial and antifungal properties.

7-Blood pressure control: Changes in the peripheral vascular bed affect blood pressure.

8-Secretion: Skin is a secretory organ by virtue of its apocrine and sebaceous glands.

9-Adnexa production: Skin produces keratinized structures such as hair, nails and the horny layer of the epidermis.

10-Storage: The skin is a reservoir of electrolytes, water, vitamins, fat, carbohydrates, protein and other materials.

11-Pigmentation: Processes in the skin (melanin formation, vascularity and keratinization) help determine the coat and skin color. Pigmentation of the skin prevents damage from solar radiation. 12-Excretion: The skin functions in some species in a limited way as an excretory organ. 13-Vitamin D production: Vitamin D is produced in or on the skin through stimulation by solar radiation. 14-Indicator The skin may be an important indicator of internal disease.

Epidermal Changes Hyperkeratosis: It is the increase of the thickening of the epidermis due to an increase in the thickening of the stratum corneum. It has 2 types: A-Orthokeratotic (anuclear) B-Parakeratotic (nucleated). NB: Hyperkeratosis may be caused either by 1-Excessive production of keratin or 2-Excessive retention of keratin (ichthyosis).

Ichthyosis: It is dryness, roughness and scaliness of the skin due to excessive retention of keratin.

Hypokeratosis: It is a decrease of the thickening of the epidermis due to decrease the thickening of the stratum corneum.

Dyskeratosis: It is lack or premature cornification (faulty keratinization). NB: Dyskeratotic cells are characterized by eosinophilic, swollen cytoplasm and condensed with dark-staining nuclei.

Acanthosis It is the increase of the thickening of the epidermis due to an increase in the thickening of the stratum spinosum.

It has 2 types A- True acanthosis: the increased thickness due to increase the number of stratum spinosum (hyperplasia). B-Pseudoacanthosis: due to hypertrophy of the cells of stratum spinosum.

NB: Epidermal hyperplasia is often accompanied by rete ridge formation (irregular hyperplasia resulting in "pegs" of epidermis that appear to project downward into the underlying dermis). Rete ridges are not found in normal haired skin of dogs and cats.

Epidermal Collarette: Refers to the formation of elongated hyperplastic rete ridges.

Pseudoepithelial Hyperplasia: It is severe acanthosis grow at the margins of burns, ulcers and inflammation.

Atrophy of the epidermis: It is a decrease of the thickening in the epidermis due to decrease in the size and/or the number of the cells (normal in dogs and cats).

Epidermal Edema 1-Intercellular Edema (Spongiosis): It is characterized by: i-a widening of the intercellular spaces with accentuation of the intercellular bridges, giving the involved epidermis a "spongy" appearance. ii-Severe intercellular edema may lead to rupture of the intercellular bridges and the formation of spongiotic vesicles within the epidermis or blow out the basement membrane and form subepidermal vesicles.

2-Intracellular Edema: It is hydropic and vacuolar degeneration and characterized by: i-Increased size, cytoplasmic pallor, and displacement of the nucleus to the periphery of affected cells. ii-Severe intracellular edema leads to reticular degeneration and intraepidermal vesicles.

Reticular Degeneration: -It is caused by severe intracellular edema of epidermal cells, in which the cells burst, resulting in multilocular intraepidermal vesicles whose septae are formed by resistant cells walls. -It may be seen with any acute or subacute inflammatory dermatosis.

Ballooning Degeneration: It is a specific type of degenerative change seen in epidermal cells with the viral infections and characterized by -Swollen eosinophilic cytoplasm without vacuolization. -Enlarged or condensed and occasionally multiple nuclei. -A loss of cohesion resulting in acantholysis.

Acantholysis (dyshesion, desmolysis, desmorrhexis): -It is a loss of cohesion between epidermal cells, resulting in intraepidermal clefts, vesicles and bullae. -Free epidermal cells in the vesicles are called acantholytic cells.

Clefts (Lacunae): They are slit-like spaces (not contain fluid) within the epidermis or at the dermoepidermal junction. Clefts may be caused by acantholysis.

Aphtha (Vesicle): A cavity containing fluid, embedded in the epidermis.

Bulla: It is a large vesicle (up to 25 Îź).

Vesicopustule: A vesicle containing large number of inflammatory cells (especially neutrophils).

Dells: Small depressions in the surface of the epidermis due to focal epidermal atrophy.

Koilocytosis: It is epidermal cells with perinuclear clear vacuolizations and condensed hyperchromatic nuclei

Erosion: Superficial loss of the epithelial covering with intact basement membrane.

Ulcer: Discontinuation of the epithelial covering, where the base lies in the dermis.

Excoriation: Erosion and ulceration produced by self trauma.

Scales: Separation of stratum corneum from the skin.

Eczema: Inflammatory condition in the epidermis characterized by redness, itching, papules, vesicles, crusts, scaling and lichenification.

Lichenification: It is thickening and hardening of the skin with exaggeration of its normal markings.

Wheal: Rounded or flat topped elevated lesions resulted from accumulation of fluid in the dermis.

Skin Rash: A temporary eruption on the skin.

Urticaria: It is Inflammatory condition characterized by edema in the dermis.

Hyperpigmentation of skin (Melanosis): It is excessive amounts of melanin in the epidermis and in the dermal melanophages. Hyperpigmentation may be focal or diffuse and confined to the basal cell layer or present throughout all epidermal layers.

Hypopigmentation: It is decreased amounts of melanin in the epidermis. It may be associated with congenital or acquired idiopathic defects in melaninization.

It is either: A-Leukoderma


Leukoderma: It is a condition in which some patches of the skin lose its melanin and appeared white in color.

Vitiligo: It is a condition in which destruction of melanocytes in small or large circumscribed area resulted in smooth and white patches of depigmentation and have hyperpigmented borders and enlarged slowly.

NB: Albinism: It is a hereditary condition associated with an autosomal recessive gene characterized by pathological absence of melanin with an individual.

Crust: It is a solid dry mass adhered with the skin surface and composed of combination of keratin, serum, cellular debris, inflammatory cells and M.O.

Types of Crusts: 1-Serous: (Mostly serum). 2-Hemorrhagic: (Mostly blood). 3-Cellular: (Mostly inflammatory cells). 4-Exudative (Serocellular): Mixture of infl. cells and Serum.

Crusts may contain important diagnostic clues: (1) dermatophyte spores and hyphae. (2) the filaments and coccoid elements of Dermatophilus

congolensis (3) large numbers of acantholytic keratinocytes. (4)Bacteria and bacterial colonies are common on the surface debris

Hydropic Interface Dermatitis: Microscopic Pictures: 1-Hydropic degeneration in the basal cell layer of the epidermis. 2-Inflammation (dilated blood vessels and leukocytes) in the dermis.

DERMAL CHANGES Collagen Changes: Dermal collagen is subject to a number of pathologic changes:

(1)Hyalinization: Increased eosinophilic, glassy, refractile appearance (seen in chronic inflammation).

(2)Fibrinoid degeneration: Focal deposition or replacement of the collagen with a brightly eosinophilic fibrillar or granular substance resembling fibrin (seen in connective tissue diseases).

(3)Lysis: Complete loss of structural detail of collagen (seen in microbial infections and ischemia).

(4)Degeneration: It is a structural and tinctorial changes characterized by slight basophilia, granular appearance, and frayed edges of collagen fibrils (seen in feline and canine eosinophilic granuloma).

(5) Dystrophic mineralization: Deposition of calcium salts as basophilic, amorphous, granular material on degenerated collagen.

(6) Atrophy: Thin collagen fibrils and decreased fibroblasts, with decreased dermal thickness.

Pigmentary Incontinence: It is the presence of melanin granules free within the subepidermal dermis and within dermal melanophages.

Dermal Edema: There are 2 types of dermal edema: 1-Perivascular edema: It is characterized by widened spaces between blood vessels and perivascular collagen.

2-Interstitial edema: It is characterized by widened spaces between the dermal collagen fibrils.

Microscopic Pictures: 1- In both types, the lymphatics are dilated (not visible in normal skin). 2- The dilated spaces and lymphatics may or may not contain pale eosinophilic homogenous material with or without fibrin.

Mucoid Degeneration: It is characterized by increased amounts of an amorphous, stringy, granular, basophilic material that separates, thins, or replaces dermal collagen fibrils and surrounds blood vessels and appendages.

Follicular Changes Poral (follicular) Keratosis: It is plugging and dilation of hair follicles with keratin. The severe condition may lead to follicular cysts.

Folliculitis: It is inflammation of hair follicles.

Perifolliculitis: It is inflammation of the surrounding tissue of hair follicles.

Furunculosis: It is penetrating or perforating folliculitis.

Alopecia: It is hairless area.

GLANDULAR CHANGES Sebaceous and apocrine sweat glands may be involved in various dermatoses.

Sebaceous Adenitis: It is inflammation of sebaceous glands (usually suppurative in acute). In chronic: it becomes: 1-Atrophic Sebaceous Adenitis: Reduce in number and size of the cells, with pyknotic nuclei. 2-Cystic Sebaceous Adenitis: The glands are dilated and lined by flattened epithelium (Senile). 3-Hyperplastic Sebaceous Adenitis: The glands showed nodular hyperplasia with epithelial infolding in the lumens.

Hidradenitis: It is inflammation of sweat glands. They became dilated or cystic.

INFLAMMATION OF THE SKIN DERMATITIS Macroscopic Pictures: dermatitis is generally characterized by the classical inflammatory manifestation, i.e., redness, heat, pain, swelling, and loss of function. Dermatitis is not diagnostic unless analyzed closely as to pattern.

Microscopic Pictures:

according to the type of


Types of Dermatitis: 1-Perivascular 5-Pustular (suppurative)

2-Diffuse 3-nodular 4-Vascular 6-Eosinophilic 7-Neutrophilic 8-Vesicular 9-Granulomatous (chronic).

SKIN AFFECTIONS 1-Environemental Skin Diseases. 2-Bacterial Skin Diseases. 3-Mycotic Skin Diseases. 4-Parasitic Skin Diseases. 5-Viral Skin Diseases. 6-Nutritional Skin Diseases. 7-Autoimmune Diseases 8-Neoplasms

1-Environemental Skin Diseases A-Sun Burns: It is characterized by 1-Severe redness of the skin. 2-Vesicles formation. 3-Water or fluid discharge. 4-Micro: Necrosis of epidermis Vesicles (cavity contain fluid). Few lymphocytic infiltration. Dilation of blood vessels.

B-Photosensitization (Photosensitizational Dermatitis):

2-Bacterial Skin Diseases Pyoderma: Any purulent skin diseases. It is either A-Primary Pyoderma: caused by single M.O. B-Secondary Pyoderma: Caused by bacterial infection secondary to skin injuries.

Causes: 1-Staph. aureus (Impetigo). 2-Strept. species.

NB: Impetigo: It is Subcorneal staphylococcal skin infection, characterized by vesicles and pustules (pyoderma), which is covered by yellow crusts. Common in puppies, kittens and piglets.

Classification of pyoderma: A-Superficial Pyoderma: It is characterized by i-Only involved the epidermis ii-Usually heal without scaring iii-Have short duration iv-Don’t involve the regional Lns. v-Not associated with systemic illness.

Macro: It is characterized by the formation of -Papules -Transient pustules -Crusts -Sometimes, localized in the ostial of the hair follicles.

Micro: They take the form either of 1-An intraepidermal pustular dermatitis or 2-Superficial folliculitis -Both with neutrophils infiltration.

B-Deep Pyoderma: i-Involves the dermis with or without subcutis. ii-Often heal with scarring. iii-Have a chronic course (long time). iv-Usually involve the regional Lns. v-Produce signs of systemic illness.

Macro: take a variety of forms including -Papules or pustules. -Subcutaneous nodules (abscesses). -Ulcers or fistulous tracts.

Micro: -Deep folliculitis and furunculosis. -Nodular to diffuse suppurative dermatitis.

Dermatophilosis: It is an acute or chronic, superficial pyoderma caused by the actinomycete, Dermatophilus congolensis. The disease affected a wide range of species in all age groups (cattle, horses, and sheep). NB:

Dermatophilus congolensis -It is a pleomorphic, Gram positive bacterium that grows as filamentous, branching septate mycelium. -It cannot penetrate healthy skin. The two most important predisposing factors in the pathogenesis of dermatophilosis are prolonged wetting and mechanical damage to the skin.

Macro: 1-Raised, roughly circular, thick, laminated, gray-brown scaly crusts on dorsal midline, flank, thoracic wall and shoulders.

2-In very severe lesions, pustules with pus discharge are seen and the hairs may be buried in thick plaques of scale crust (Paint brush or matting hair). So, it is called Lumpy wool disease in sheep. 3-When individual crusts are forcibly detached, the hair is also epilated (Alopecia). 4-The underlying epidermis is moist and erythematous.

Micro: 1-Folliculitis and furunculosis. 2-Epidermal multiplication (palisading crusts). It consists of layer of keratin with layer of leukocytes and necrotic debris. 3-Hyperkeratosis (ortho- and parakeratotic types). 4-Intense aggregation of neutrophils.

3-Mycotic Skin Diseases Fungal diseases are divided into three categories: 1-Superficial mycosis: invade the skin and its appendages eg. Dermatophytosis. 2-Subcutaneous mycosis: mostly saprophytic (not produce disease). 3-Systemic mycosis: saprophytic fungi. Induced severe disease in immunosuppressed animals.

Dermatophytosis (Dermatomycosis or Ringworm): It is a superficial infection of the keratinized layers of the skin and its appendages by a group of dermatophytes. Causes: Dermatophytes are 3 genera:

1-Microsporum 2-Trichophyton 3-Epidermophyton

NB: Dermatophytes do not invade living tissue but remain confined to the keratinized layer, which they attack with proteolytic enzymes having keratinolytic activity.

Macro: 1-Circular areas of alopecia. 2-Scales, crusts and pustules or ulceration.

Micro: 1-Branched, septated hyphae on the surface or in the hair follicles. 2-Round or oval arthospores either within the hair (endothrix) or on the external surface (ectothrix). Microsporum is ectothrix Tichophyton is endo and ectothrix 3-Ortho- and parakeratotic hyperkeratosis

4-Parasitic Skin Diseases Mange (Cutaneous Acariasis): Sarcoptic Mange: Causes: Sarcoptes scabei is responsible for scabies in humans and sarcoptic mange in domestic animals.

Macro: 1-In the early stages: they include erythematous papules, excoriations, hemorrhagic crusts, traumatic erosions (induced by pruritus) and patchy alopecia. 2-In chronic lesions: they include marked alopecia, scaling and lichenification.

Micro: 1-Thick scale crust composed of ortho and parakeratotic hyperkeratosis, serum lakes, neutrophilic debris, and numerous refractile Sarcoptes ova.

2-Acanthosis and rete-ridge formation. 3- Adults, nymph and eggs are seen on the epidermal surface or within tunnels of keratin. 4-Dermal lesions include variable vasodilation, endothelial swelling, edema, fibrosis, perivascular mononuclear-cell and neutrophils infiltrations.

Demodectic Mange: Causes: Demodex mites are normal inhabitants of the hair follicles or sebaceous glands. D. folliculorum and D. canis (dogs) and D. bovis (cattle).

Lesions: 1-Mites (cigar-shaped) in the hair follicles or sebaceous glands. 2-Alopecia, scaly and eroded skin (epidermis). 3-Suppurative and granulomatous reaction. 4-Deep folliculitis and furunculosis.

Psoroptic Mange: Psoroptes ovis and P. cuniculi are infect sheep, cattle and rabbits, where it lives in the external meatus and produce severe lesions that may lead to middle or inner ear infection, and death. Psoroptes species do not burrow into the epidermis, but remain on the surface.

Chorioptic mange: This type is caused by Chorioptes and localize on the legs of the horse, cattle and sheep inducing “Foot-Mange or Leg itching�.

Notoedric Mange: It occurs around ears, face and neck of cats and rats.

Otodectic Mange: It occurs in ear canal of dogs and cats, producing hematoma of the pinna due to head shaking and scratching. Otitis media or interna and encephalitis (non-suppurative) are present beside the mites.

Psorergatic Mange: This type localizes on the skin surface of sheep, causing pruritis and dermatitis.

5-Viral Skin Diseases Poxivirus Infection Contagious ecthyma ("Orf")

Pseudocowpox Sheeppox Lumpy Skin Disease


6-Nutritional Skin Diseases Vitamin A deficiency: It induces squamous metaplasia, a marked scaling and crusting dermatitis beside follicular hyperkeratosis .

Zinc Deficiency (Parakeratosis): Initial gross lesions consist of erythema, and excessive sebaceous secretion. Later, there is excessive growth and keratinization of skin epithelium with the formation of horny crust and fissures.

Microscopically, there is acanthosis, parakeratosis, and keratinization.

8-Neoplasms Epithelial tumors:

(sq. c. papilloma, sq. c. carcinoma, Basal c. carcinoma, adenoma, adenocarcinoma and melanoma).

Connective Tissue tumors: (Fibroma, lipoma, lymphoma, histiocytoma, myloma, fibrosarcoma, liposarcoma and mast cell tumor). Dermoid cysts are also recorded.

Please Answer the following questions: Define the following: Hyperkeratosis Dyskeratosis Acanthosis Epidermal Collarette Reticular degeneration Ballooning degeneration Spongiosis Koilocytosis Excoriation Lichenification

Write Short Notes on: Epidermal and Dermal Edema Pathological changes of dermal collagen. Pyoderma (types and lesions). Dermatophilosis Dermatophytosis

The pathology of skin  
The pathology of skin  

pathology diagnosis of skin affections