This document provides an overview of pathology of the skin and appendages. It discusses the structure and functions of the epidermis, dermis and subcutis. It then covers various dermatohistopathological changes that can occur in the epidermis including hyperkeratosis, dyskeratosis, acanthosis and more. Congenital and hereditary diseases of the skin are also reviewed. The document further examines disorders of epidermal differentiation, physiochemical diseases, actinic diseases, nutritional diseases and more. Specific conditions discussed include seborrheic dermatitis, leukoderma, thermal and chemical injuries, photosensitization and contagious pustular dermatitis.

1. Pathology of Skin
and Appendages

2. I. Generl Considerations

3. Functions
Economic Importance

6. epidermis
 Stratum basale, spinosum, granulosum,
cornium
 Keratiocytes 85%
 Melanocytes (5-8%)
 Langerhan’s cells (5%)
 Merkel cells (tactile cells)
 Indeterminate dendritic cells

7. Dermis
 Collagens
 Glycosaminoglycans
 Cutaneous vasculature
 Hair follicles
 Simple – horse and cattle
 Compound – sheep, goat, dogs, and cats
 Sebaceous glands
 Sweat glands
 Arrector pilli muscle

8. Subcutis
 Adipose tissue supported by fibrous
tissue, containing blood vessels

9. II. Dermatohistopatholgy

10. A. Epidermal Changes
 Hyperkeratosis
 Orthokertosis – anuclear – hyperkeratosis
 Parakeratosis – nucleus
 Diffuse
 Ectoparasitism
 Zinc-responsive
 Vit. A responsive
 Thallotoxicosis
 Dermatophilosis-Dermatiphilis congolensis
 Dermatophytosis-Epidermophyton, Microsporum, and
Trichophyton
 Focal
 Idiopathic seborrheic dermatis of dogs and horses
Cont…..

11.  Hyperkeratosis
 decreased synthesis of epidermis –
 seborrheic and other exfoliative skin disorders
 Dyskaratosis
 Premature And Faulty Keratinization Of Individual
Cells
 Dyskaryotic cells are eosinophilic, swollen, with
dark-staining nuclei
 Hypergranulosis and hypogranulosis
 Increased or decreased thickness of stratum
granulosum
Cont…….

12.  Acanthosis (hyperplasia)
Stratum spinosum
 Irregular (uneven, elongated, pointed rete ridges)
 Regular
 Papillated
 Psuedo-carcinomatous or pseudoepitheliomatous
(extremely irregular hyperplasia)
Associated with Chronic inflammatory processes
Cont……

13. Congenital and
Hereditary Diseases of
Skin

14.  Epitheliogenesis Imperfecta
 Discontinuities of squamous epithelium
of skin and oral mucous membrane
 Ichthyosis
 Fish scale like lesions (hyperkeratosis)
mostly genetic skin disorders
 Hereditary zinc deficiency
 Less Absorption of zinc (parakeratosis)
 Congenital Hypotrichosis
 Partial or complete absence of hair
(alopecia)
 Genetic (more frequent in cattle)
 Non genetic
 Iodine deficiency
 Adenohypophyseal hypoplasia

15.  Hypertrichosis
calves and lambs
 Episodes of repeated maternal hyperthermia
 Congenital hypertrichosis of horse
 Pituitary tumors in old horses
 Epidermolysis bullosa
 Group of inherited disorders causing blisters
following minor injury in many species of
animals

16.  Familial Canine Dermatomyositis
 Autosomal dominant in Colie and
Shetland dogs
 Lesions (alopecia and crusting) start
at the age of few months
 Hereditary Collagen Dysplasia
 Complex disorders of CT, which
results in a decrease in tensile
strength of affected tissue (fragility
and hyperextensibility
 Many species are affected

17. III. Disorders of Epidermal
Differentiation
A. Seborrheic skin disease / ` Primary
idiopathic Seborrhea – altered
keratinization – dandruff, scaling, crusting
 Hormonal imbalances
 Hypothyroidism
 Hyperadenocorticism
 Sex hormonal imbalances
Cont…..
Filagrin + colesterol + other lipids + keratin = keratinization
Granulosa
Spinosum - Keratin

18.  Ectoparasitism
 Endoparasitism
 Dermatophilosis
 Hypersensitivities
 Abnormal lipid metabolism – malabsorption, pancreatic and liver
diseases, diabetes mallitus
 Dietary def. of fatty acids, protein, vitamin A, zinc
 Chronic catabolic states
 Environmental factors – hot and dry conditions
1. Seborrhoea sicca – focal or diffuse flaking (non-adherent)
2. Seborrhoea oleosa – flaking + liquid production
3. Seborrheic dermatitis – scaling, greasiness, and inflammation

19.  Leukoderma and leukotrichia
 Hereditary Hypopigmentation
 Piebaldism -- autosomal dominant disorder
(hypomelanosis)
 Albinism – inability to synthesize tyrosinase,
melanosome failure, autodegradation
 Chediac-Higashi syndrome – (autosomal recessive
disorder) melanin not passed to keratinocytes
 Acquired Hypopigmentation
 Damage to epidermal melanin unit by various insults
 Horses – harness
 Dogs – immune mediated diseases
 Copper deficiency

20. VI. Physiochemical Diseases of Skin
 Physical Injury to Skin
 Mechanical, Frictional, Traumatic, and Psychogenic
 Callosities - hyperkeratosis
 Hygroma – acquired bursa over bony prominences
 Decubitus ulcers – ischemic necrosis – prolonged recumbancy
 Psycogenic – cats – neurodermatitis (feline hyperesthesia)
 Injection-site reaction – nodules – ulcers or fistulae
 Acral lick dermatitis – hyperplastic disorder
 Udder and tail
 Cold injuries – vascular injury - anoxia
Pressure, Vibration, Electricity, High and low ambient temperature,
humidity, visible light, ultraviolet light, infra red, ionizing radiation, and chemicals

21. Thermal injuries
Dry heat - Desiccation and carbonization
Boiling or coagulation
 First degree – epidermis – erythemia, edema –
no vesicles – no injury to epithelium
 Second degree – coagulative effects on
epithelium, marked dermal edema, vescles and
bullae
 Third degree – full thickness is affected
 Forth degree – subcutaneous tissue is also
affected

22. Chemical injuries
 Primary contact irritant dermatitis – acids, alkalies, tar,
paints, kerosene, turpentine, antiseptics, insecticides,
feces, urine
 Thallotoxicosis – rodenticide – combining with
sulfdydral groups – thallium replaces potassium –
commissures or nasal cleft – erythemia, ulceration,
alopecia
 mercury
 Arsenic
 Iodine
 Selenium
 Chlorenated naphthalenes
 ergotism

23. VII. Actinic Diseases of Skin
 Direct effect of solar radiation
 Short wave ultravoilet radiation 290-320 nm (UV-B)
 < 290 (UV-A) absorbed by ozone layer
 > 320 (UV-C) long wave – photodynamic agents
 Short term effects - cytokines from keratinocytes
 Erythema (direct damage to endothelium),
 Hyperplasia
 Melanosis
 Depress immune reaction
 Long term effects
 Degeneration, mutagenesis
•Solar dermatitis – sun burn – cats and goats
•Solar elastosis – cancer - humans
•Solar kertosis – preneoplastic hyperplasia - dogs

24.  Enhanced susceptibility of skin to actinic
radiation - exacerbated form of sunburn,
caused by the activation of photodynamic
chemicals
 Action spectrum  reactive oxygen species
Photosensitization

25.  Primary Type I–exogenous pigments
 Hypericin, fagopyrin, furocoumarin (dianthrone
Derivatives-from plants- a laxative agent)
 Phenothiazine
 Secondary Type II – Aberrant endogenous
pigments act as photodynamic agent
 Bovine congenital erythropoietic porphyria – def.
of uroporphyrinogen III cosynthetase, a key
enzyme in heme synthesis –
osteohemochromatosis
 Bovine erythropoietic protoporphyria – def. of
ferrochelatase – protoporphyrin IX
 Type III - phylloerythrin degradation product
of chlorophyll – failure of liver to eliminate
phylloerythrin

26. Photosensitization

27. VIII. Nutritional Diseases
of Skin
 Protein-Calorie Deficiency
 Loss of adipose tissue, dull, dry, and brittle
hair coat, alopecia
 Fatty acid Deficiency
 General dietary def., malabsorption, liver
disease
 Diffuse scaling and alopecia

28.  Hypovitaminosis and Vitamin-Responsive
Dermatoses (Vit. A and E)
 Mineral deficiency – Iodine, cobalt,
copper, and zinc (wool and hair coat,
component of metalloenzymes, cofactor,
regulate DNA and RNA metabolism) -
hyperkeratosis

29. contagious pustular
dermatitis
Orf is an exanthemas
disease caused by a parapox
virus and occurring primarily
in sheep and goats
Papules and Pustules
lips and muzzle
Inter digital spaces, Udder --
--may result in Mastitis
Contagious Ecthyma