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sunteti aici: Home » Specialisti veterinari » Perfectionare continua » Dermatologie » Dermatologie veterinara Curs 1 - Introducere in dermatologie

Dermatologie veterinara Curs 1 - Introducere in dermatologie

Lecture 1 - Introduction to Dermatology: Structure, Function, and Terminology

I. The Dermatologic Exam

A. History

1.  Signalment
It is important to note age, breed, and sex as these factors may be important in recognizing the predilection towards specific dermatologic conditions.

2.  History concerning the skin lesion

a.  The lesion(s)
Obtain information concerning the location of initial lesion, initial appearance, rate of progression, pattern of progression, degree of pruritis, location of pruritis, and contagion to other animals or humans in household.

b.  Other influencing factors
Question the owner about ectoparasite control, travel history, seasonal influences, environmental influences (indoor, outdoor, bedding, etc.), and the effect of diet or medications on the lesions.

3.  Presence of other underlying disease: obtain a thorough history to rule-out disease in other organ systems.
Must be able to answer the question: "Is this dermatologic condition the primary problem, or does my patient have underlying systemic disease with a dermatologic manifestation?"
*Q: What types of systemic diseases may have cutaneous manifestations?

B. Physical exam

1.  General appearance
Does your patient appear to be a healthy animal with a dermatologic complaint or is there overt evidence of generalized poor general health?

2.  Dermatologic exam

a.  From a distance: determine the overall distribution of the skin lesions.

b.  Up close and personal
More closely examine the regionally affected areas. Evaluate body regions of the skin (face, ears, hair, ventrum, mucocutaneous junctions, nail beds, and digits) during your exam. *Q: Why is it important to evaluate these specific areas?

c.  Hair: note texture (dry, oily), ease of epilation, presence of alopecia, and degree of dryness. *Q: What might easily epilated hairs imply?

d.  Skin: note thickness, pigmentary characteristics, sebum production, elasticity, heat production, and configuration of skin lesions.

e.  Evaluate if the skin lesions are primary or secondary.

3.  Thorough physical exam: to evaluate for underlying disease.

C. Diagnostic Evaluation

1.  The "core" tests: tests routinely performed in the evaluation of the patient with a dermatologic complaint.

a.  Skin scrapings:

i.  Indications: primarily used to detect mites (Demodex, Sarcoptes, etc.).

ii.  Technique: moisten scalpel blade with small amount of oil, grasp skin between fingers, squeeze, and scrape. The process is not painful, but should be deep enough to cause capillary bleeding. *Q: Is it possible to have false negative results?

b.  Cytology

i.  Indications: used to assess characteristics of discharge or mass lesion (inflammatory, neoplastic, cystic, etc).

ii.  Technique: collect sample via aspiration (22G needle and 12 cc syringe) or via scraping of exudative skin lesion (mix with small amount of saline on slide, air dry, and stain with DiffQuik stain).

c.  Dermatophyte test media (DTM) culture

i.  Indications: diagnosis of dermatophytosis (see lecture 3).

ii.  Technique: see lecture 3

d.  Trichogram: microscopic examination of hairs

i.  Indications: may provide clues as to cause of alopecia. Normal animals exhibit hairs in various stages of the growth cycle (anagen, telogen). Patients with endocrine disease or systemic illness often have a predominance of hairs in telogen, while those with other causes of hair loss often have a mixture of hairs in telogen and anagen phase.
ii. Technique: use hemostat to grasp hair close to skin surface and pluck (note ease of epilation). Put hair on slide with mineral oil and coverslip. View under 40X. Telogen bulb (photo on right) is spear shaped, rough and non-pigmented. Anagen bulb (photo on left) is expanded and often pigmented.


e.  Skin biopsy

i.  Indications: to evaluate for disease of unknown etiology, suspected neoplasia, immune-mediated disease, or disease that is non-responsive to therapy.

ii.  Technique: gently clip or cut hairs, do NOT prep skin surface, infiltrate local lidocaine and use either 6 mm biopsy punch (press firmly and rotate punch in one direction - not back and forth), or elliptical skin incision technique. Gently remove sample without crushing.

2.  Additional tests
The following tests may be helpful in the diagnosis of specific dermatoses (as indicated by signalment, history, physical exam and dermatologic exam findings - see later lectures): minimum data base (CBC, profile, UA), endocrine testing, bacterial culture, biopsy, lymph node aspirates, immune testing, and serology.

D. Morphology of skin lesions

1.  Primary lesion
Primary skin lesions develop as a direct reflection of underlying disease and may suggest a specific dermatosis.

2.  Secondary lesion
Secondary skin lesions evolve from primary lesions (through degeneration, trauma, etc.) or result from artifacts induced by the patient or the client (licking, scratching, secondary infection, medications, etc.).

II. Terminology

A. Primary lesions

1.  Macule: a flat circumscribed spot up to 1 cm in diameter characterized by a change in color.

2.  Patch: a macule > 1 cm in size.

3.  Purpura: a type of macule caused by bleeding into the skin.

4.  Papule: a small, solid elevation of the skin up to 1 cm in diameter. Many are pink or red in color.

5.  Plaque: a larger flat-shaped elevation formed by the coalition of papules.

6.  Nodule: a circumscribed solid elevation > 1 cm in diameter that usually extends into the dermis or subcutis.

7.  Tumor: neoplastic enlargement.

8.  Cyst: an epithelial-lined cavity containing fluid or solid material.

9.  Pustule: a small, circumscribed elevation of the epidermis filled with pus.

10. Abscess: a demarcated fluctuant lesion resulting from the dermal or subcutaneous accumulation of pus.

11. Wheal: a sharply circumscribed raised lesion consisting of edema that tends to resolve quickly.

12. Vesicle: a sharply circumscribed elevation of the epidermis filled with clear fluid.

13. Bulla: a vesicle > 1 cm in diameter.

B. Secondary lesions

1.  Scale: an accumulation of loose fragments of the horny layer of the skin.

2.  Epidermal collarette: a type of scale arranged in a circular rim of loose keratin flakes - represents the remnants of a vesicle, bullae, or pustule.

3.  Crust: occurs when dried exudate, serum, pus, blood, etc. adheres to the surface of the skin and hairs.

4.  Scar: an area of fibrous tissue that has replaced normal tissue after injury.

5.  Excoriation: linear erosion (abrasion) of the skin induced by scratching or self-trauma.

6.  Erosion: a shallow ulcer (loss of the superficial part of epidermis, does not penetrate dermis).

7.  Ulcer: loss of the epidermis with exposure of the underlying dermis.

8.  Lichenification: a thickening and hardening of the skin which follows chronic skin inflammation - note exaggerated skin markings.

9.  Hyperpigmentation: increased melanin in epidermis and sometimes dermis. Often occurs with chronic inflammation, post-trauma or in association with endocrine disorders.

10. Comedo: a dilated hair follicle filled with cornified cells and sebaceous debris.

11. Fissure: linear cleavage (cracks) in the epidermis or dermis caused by disease or injury.

12. Erythema: reddening of the skin.

13. Follicular cast: an accumulation of keratin and sebaceous material adherent to a hair shaft. May be a primary (vitamin-A responsive dermatoses, primary seborrhea) or secondary (demodex, dermatophytes) skin lesion.

Goals of Lecture 1 - Dermatology introduction

References (for all dermatology lectures): Muller & Kirk's Small Animal Dermatology 5th edition 1995. Kirk's Current Veterinary Therapy XII. Bonagura. W.B. Saunders Co. 1996. WB Saunders Co. Selected excerpts from ACVIM 1995 and 1996 proceedings, and JAVMA, JIVM, and Compendium 1992-2006. Small Animal Dermatology Secrets: Karen L. Campbell 2004. Skin Diseases of the Dog and Cat Richard Harvey, Patrick McKeever 2003. Small Animal Dermatology A Color Atlas and Therapeutic Guide Linda Medleau, Keith Hnilica 2001. Supplemental information also provided courtesy of Dr. Danny Scott and Dr. Miller, Cornell University.

1.  What 3 areas should your history taking of the dermatologic patient cover? (A .1. 2. 3.) - generalities only. Be able to recognize the components of a complete dermatologic exam. (B.2. all).

2.  What are the 5 basic "core" tests utilized in the evaluation of a patient with a dermatologic complaint? Be able to describe indications and technique for these tests (C.1.a. through e.)

3.  How does the root of a hair plucked in telogen differ from the root of a hair plucked in anagen? How is this information helpful in the diagnostic work-up of the patient with alopecia?

4.  What is the difference between a primary and secondary skin lesion? (be able to define these terms)

5.  Be familiar with the definitions of specific primary and secondary skin lesions (II.)


Appendix

I. General functions of the skin

A. Barrier and protector

The skin provides a barrier to the outside world and houses all the internal organs. It acts to protect against physical insults, chemical insults, and pathogenic microorganisms.

B. Sensory organ

The skin is the largest organ in the body. It senses heat, cold, pain, pruritis, touch, and pressure.

C. Temperature regulation

The skin plays an important role in temperature regulation via modifying cutaneous blood flow, sweat gland production, and the elaboration of a hair coat.

D. Immunosurveillance

The Langerhans cells, lymphocytes, and keratinocytes of the skin play an important role in the immunologic defense of the body.

E. Vitamin production

Under the influence of sunlight, the skin produces vitamin D3 from precursors in the skin.

F. Electrolyte regulation

The skin acts as a reservoir of water, electrolytes, fat, and other substances. It also has limited excretory capabilities via apocrine, sebaceous, and sweat glands.

G. Hair: the skin produces pigmentation and keratinized structures including hair and nails.


II. Anatomy and physiology: hair

A. Hair growth: occurs in cycles - not continuously.

There are three phases of hair growth: anagen (growth phase), telogen (rest phase), and catagen (stage in between).

B. Anatomy

1.  Structure

a.  Hair shaft: composed of an inner medulla, middle cortex, and outer cuticle.

b.  Hair follicle: serves to anchor the hair shaft in the dermis.
The anagen hair follicle extends into the deep dermis. The lowest part of the hair follicle is the dermal hair papilla.

c.  Dermal hair papilla: hair grows from a layer of cells that covers the papilla.

2.  Types of hair: the normal haircoat consists of primary and secondary hairs.

a.  Primary hairs: coarse guard hairs or outercoat.

b.  Secondary hairs: fine hairs or undercoat.
In cats, the secondary hairs are more numerous than primary hairs. In dogs, the ratio varies depending on the type of haircoat.

3.  Color of haircoat: genetically determined and occasionally temperature-dependent.
In some cats (Siamese, Himalayan, etc.) there is a temperature dependent enzyme that converts melanin precursors into melanin. Warm temperatures = light colored hair, cool temperatures = dark colored hair.

4.  Structures associated with individual hairs

a.  Arrector pili muscles
These muscles are innervated, play a role in thermoregulation, and contract in response to catecholamines, producing piloerection.

b.  Glandular structures: see later.

 

C. Factors which influence hair growth

1. General

The hair cycle is controlled by the photo-period, ambient temperature, hormones, nutritional status, and other factors.

Anagen (hair growth) is stimulated by thyroid hormones and inhibited by excess glucocorticoids and estrogens.

2. Malnutrition: poor quality haircoat

Hair is predominantly protein and malnutrition has a profound effect on the quality of the haircoat - often resulting in a dull, brittle or thin haircoat.

3. Illness: excess shedding

During ill health, the anagen phase is often shortened and most hairs are in telogen. These hairs are lost more easily - and thus the ill animal is often observed to have "increased shedding."

Severe illness may result in "telogen defluxion," a condition whereby many hairs synchronously enter telogen and are shed together.

4. Microscopic appearance of hair root (see above)

5. Hair regrowth: no new hair follicles are formed after birth.

Hair growth cycles occur due to the repeated induction of the hair follicle.

Hair grows until it reaches its preordained length (genetically determined), then enters the resting phase, then is shed.

Regrowth of a normal or short haircoat after shaving may take 3 - 4 months (or longer in long-coated breeds).


III. Anatomy and physiology: skin

A. Overview

In general, skin thickness decreases dorsally to ventrally on the trunk and proximally to distally on the limbs.

Skin consists of 3 specific layers: epidermis, dermis, and subcutis. This dermis constitutes the bulk of skin thickness in any one area.

B. Epidermis: outermost layer of the skin

1.  Cell types
Consists of four basic cell types: keratinocytes (about 85% of cells - produce keratin), melanocytes (produce melanin), Langerhans' cells (important in cutaneous immunosurveillance), and Merkels cells.

2.  Cell layers: from inner to outer

a.  Basal layer: separates epidermis from dermis and serves to replenish the epidermal cells.

b.  Spinous layer: consists of daughter keratinocytes and Langerhans' cells.

c.  Granular layer: flattened cell layer.

d.  Clear layer: compact layer of anuclear keratinized dead cells.

e.  Horny layer (stratum corneum): outer layer of keratinized tissue that is constantly being shed. These tightly packed cells are infiltrated by an mixture of sebum and sweat that helps to form a physical barrier.

3.  Function of the epidermis
The epidermis produces the protein keratin which acts as a major barrier between the animal and the environment.

4.  Epidermal turnover
The average turnover time from basal layer to granular layer in dogs is 22 days (although turnover time in seborrheic Cocker spaniels can be as short as 7 days).
Various hormones influence epidermal proliferation, differentiation, and keratinization.

5.  Resident microflora
There is a normal population of resident microflora on the skin that helps to prevent colonization by pathogenic organisms.
The single most important factor causing overgrowth of microorganisms on the skin is increased skin moisture.

C. Basement membrane

This layer functions to anchor the epidermis to the dermis, acts as a barrier, and helps with wound healing. It consists primarily of collagen, proteoglycans, and other substances.

D. Dermis

1.  Anatomy
The dermis is composed of fibers (collagenous fibers most numerous), ground substance, cells, lymphatics, small blood vessels, and epidermal appendages.

2.  Function
The dermis allows for the diffusion of nutrients and electrolytes to the upper avascular epidermal layer and acts to maintain and repair the skin.

E. Glandular structures

1.  Sebaceous glands

a.  Location: found throughout haired skin - ducts open into the hair shaft.

b.  Function
Produce an oily secretion (sebum) which spreads over the stratum corneum and helps to retain moisture as well as has some antimicrobial action.
Secretion of sebum is stimulated by androgens and inhibited by glucocorticoids and estrogens.

2.  Apocrine sweat glands

a.  Location: as for sebaceous glands.

b.  Function: role still debated - probably have pheromonal and antimicrobial properties.

3.  Eccrine sweat glands

a.  Location: found only in the footpads - duct opens directly onto surface of footpad.

b.  Function: these glands sweat in response to agitation and likely play a role in thermoregulation and heat dissipation.

c.  In general, dogs and cats do not have the ability to sweat as an effective means of temperature control as can humans.

F. Subcutis (hypodermis)

This is the deepest and thickest layer of the skin. It contains fat and connective tissue and serves primarily as protection (padding for the body), insulation, and as an energy reserve.

 

 

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