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Basics of dermatology: Clinical evaluation and in-office diagnostics (Proceedings)
History (70% of the battle); physical examination (20% of the battle)
History (70% of the Battle)
1. Age (e.g., genodermatoses, demodicosis and dermatophytosis young: hormonal abnormalities and tumors old).
2. Sex (e.g., sertoli cell tumor male: ovarian imbalance female).
3. Breed (e.g., atopy terriers, Shar Peis, retrievers, and dalmatians: acanthosis nigricans doxies).
4. How long has it been going on?
5. Where did it begin?
6. What did it look like when it began?
7. How has it progressed?
8. Has it ever been pruritic? If so, where? Is it an itch that rashes, or a rash that itches?
9. Are other animals affected (contagious?) now or do related animals have a similar disorder, i.e., familial?
10. Do owners have lesions?
11. Diet (any changes preceding or since problem? What effect?).
12. Environment indoor (What has changed? What is there?), outdoor (What has changed? What is there?).
13. Seasonal or nonseasonal?
14. Treatments given (What? How much? How long? When? What effect?).
15. Any other signs of disease? (Do not forget the rest of the body!!).
16. Previous medical/surgical problems.
Physical examination (20% of the Battle)
1. Good lighting essential (positioning, magnification, clipping, may be important).
2. Look at entire animal from a distance (other noncutaneous signs of disease?).
3. Symmetry (symmetrical? asymmetrical?).
4. Distribution of lesions (ventral, dorsal, etc.).
5. Configuration of lesions (linear; annulararciform; grouped).
6. What are the lesions.
7. Remember! With the skin, you have the entire organ in front of you, pathology readily visible: your eyes are the single most important physical diagnostic aid at your disposal.
Primary the direct reflection of the underlying disease
a. Macule well circumscribed, flat area of color change less than or equal to l cm diameter (e.g., increase or decrease in pigmentation).
b. Patch a large macule (greater than 1 cm diameter).
c. Papule well circumscribed, solid (due to increase in cells), usually red elevation in the skin, less than or equal to l cm in diameter; can be any color, can be subcutaneous; imperative to determine whether these are follicular (infection) or nonfollicular (allergy).
d. Plaque similar to papule, but greater than l cm in diameter, and flattopped.
e. Nodule well circumscribed, solid, elevated (large papule) or subcutaneous mass; greater than l cm in diameter; may or may not be ulcerated, alopecic, discolored, etc.
f. Tumor vague term; actually encompasses nodule size and up.
g. Pustule as for papule, but filled with pus (usually yellowish) (hallmark of bacterial infection, i.e., pyoderma).
h. Wheal well circumscribed, variable sized, raised, flattopped, evanescent, straightwalled lesion, containing edema fluid (clear ( blood; the overlying skin/haircoat are normal; fluid is distributed throughout dermis, therefore, cannot be liberated by cutting into lesion; (often associated with allergy).
i. Vesicle as for papule, but filled with clear fluid (serum); less than or equal to l cm in diameter. (Think viral, irritant, autoimmune).
j. Bulla (blister) as for vesicle, greater than l cm in diameter.
Lesions that result secondary to healing, traumatization, secondary infection, medication, etc., of the primary lesions.
a. Scale (flake) accumulation of loose fragments of the horny layer (stratum corneum): indicates increased or altered epidermal maturation and turnover time. Note: scales can be primary lesions (e.g., keratinization defects).
b. Hyperkeratosis - thickened, adherent horny layer: indicates increased or altered epidermal maturation or turnover time. Note: hyperkeratosis can be a primary lesion (e.g., keratinization defects).
c. Crust (scab) dried consolidations on skin (exudate, bugs, serum, blood, pus, scales, medication, etc.), thicker and more tightly adherent than scale.
d. Scar area of fibrous tissue replacing damaged dermis and/or subcutis. (Usually atrophic and depigmented; horse may be proliferative).
e. Erosion loss of epidermis down to basement membrane (no scar).
f. Ulcer loss of tissue below basement membrane (may scar).
g. Excoriation erosions and ulcers due to selfinflicted trauma (think pruritic disease).
h. Lichenification thickened, hardened skin, with exaggerated markings (hallmark of chronic inflammation).
i. Fissure crack in skin secondary to loss of tone associated with inflammation.
j. Comedone follicular plugging with excessive keratosebaceous material. Note: comedones can be primary lesions (e.g., feline acne, schnauzer comedone syndrome).
k. Pigmentary disturbance hyperpigmentation (melanosis) affecting skin (melanoderma), hair (melanotrichia), or both (especially chronic inflammation and endocrinopathy); Hypopigmentation (hypomelanosis) affecting skin (leukoderma, achromoderma), hair (leukotrichia, achromotrichia), or both (especially inflammatory and endocrine).
l. Alopecia complete absence of hair from where normally present; hypotrichosis implies less than normal; inflammatory, endocrine, developmental. Note: alopecia can be a primary lesion (e.g., follicular dysplasia, alopecia areata).
m. Epidermal collarette circular rim of peeling epidermis surrounding a recent erosion or ulcer ("footprint" of prior pustule, vesicle, bulla).
n. Changes in elasticity, extensibility, and thickness loss of elasticity (hypotonia) associated with hyperglucocorticoidism, hyposomatotropism, catabolic states, senility; hyperelasticity and hyperextensibility associated with developmental defects; thin skin associated with hypergluco-corticoidism, hyposomatotropism, catabolic states, senility; thick skin associated with chronic inflammation, edema, hypothyroidism (mucinosis) and acromegaly.
o. Quality of hair coat dry, dull, brittle, easy epilation common to many inflammatory and hormonal dermatoses.
p. Hyperhidrosis excessive sweating associated with many inflammatory dermatoses (especially canine atopy).
q. Nikolsky sign normalappearing skin is dislodged with lateral digital pressure (think pemphigus and toxic epidermal necrolysis).
The most widely used aid, one of the simplest and least expensive; like other laboratory examinations, it serves two purposes:
a. Definitive diagnosis if etiologic agent found such as mites, fungi, helminths.
b. Equally valuable negative results, thus eliminating some of the diagnostic possibilities; must be kept in mind that can be a false negative either due to inadequate or poorly taken sample, or incompetence on the part of the person performing the test; scrapings may be superficial (yeast, some ectoparasites) or deep (most ectoparasites). Deep scrapings should:
1. Be made at periphery of lesion.
2. Be made after squeezing fold of skin.
3. Be deep enough to draw blood (include epidermis, dermis, and hair); material usually suspended in mineral oil; pick primary, unexcoriated lesions.
(By direct impression, or aspiration techniques) when used in combination with special stains, are helpful in the rapid diagnosis of certain:
a. Neoplasms (mast cell tumor, lymphoma, histiocytoma, TVT).
b. Infections (yeasts, bacteria, mycobacteria, protozoa).
c. Autoimmune disorders (pemphigus).
Groups of hairs are plucked, aligned in mineral oil, and examined microscopically for evidence of infection (dermatophytosis, piedra), shaft defects, growth stage, and external trauma.
Ultraviolet source used in diagnosis of dermatophytosis; positive test yellowgreen fluorescence of hairs down to level of epidermis and below (false fluorescence common, especially scales, dirt, medications; usually bluish or purplishwhite); only Microsporum canis, M. audouinii, and M. distortum fluoresce; M. canis is main veterinary pathogen, and only some of these will fluoresce (50% of cats, 30% of dogs); thus, positive is quick and easy, but negative means nothing). Virtually worthless in large animals. Need to allow lamp to "warm up", and may need to expose suspect hairs for a few minutes.
Skin scrapings and plucked hairs cleared with 10% KOH (30 minutes at room temperature, few seconds by gentle heating); other clearing agents available; mainly for dermatophytosis; requires trained eye, and still only 60% accurate when compared with culturally proven infections! Best in horse and cat. In veterinary medicine, no better than trichography.
Skin scrapings and plucked hairs (especially fluorescent ones) placed on fungal media (( color indicator); the most accurate method for diagnosis of dermatophyte infection, but beware of simple carriage or recent exposure; sample untreated lesions, take a few, sick hairs; soak area to be sampled with alcohol and let airdry prior to sampling. "Color-coded" media not as accurate as Sabouraud's.
Bacterial culture and susceptibility testing
Fraught with hazards; any moist cutaneous lesions older than 24 hours will produce coag + staph and/or Bhemolytic strep; to interpret significance of culture as far as the pathogenic role the bacteria are playing, is necessary to know exactly how culture taken and the number of bugs recovered; always culture from primary, unexcoriated lesion; simple Diff-Quik or gramstained smear will frequently give you the same, and more reliable, information.
Scotch tape preparation
Great for surfaceliving ectoparasites (fleas, lice, Cheyletiella spp., Otodectes, Lynxacarus, chiggers); clear scotch tape is touched to skin and hair in several areas, pressed onto a glass slide, and examined under the microscope.
Rapid combing will trap fleas and flea dirt, also useful for surface-living ectoparasites (direct examination or KOH digestion of hair and debris).
Useful in distinguishing between hemorrhage and vascular dilatation as causes of erythema; glass slide is pressed over area; blanching = vascular dilatation, nonblanching = purpura (bleeding diathesis versus vasculopathy).
Hard and fast rules on what cutaneous diseases should be biopsied cannot be made, but general guidelines would include:
a. All obviously neoplastic or suspected neoplastic lesions.
b. All persistent ulcerations.
c. Any case that in the experience of the clinician is obviously unusual, or appears quite serious.
d. A disease that is not responding to apparently rational treatment.
e. Any suspected diagnosis in which the treatment is expensive enough or time consuming enough to demand a definitive diagnosis before beginning.
Take the most developed primary lesion without secondary changes; if the disease is widespread, take two to three samples of lesions in various stages; biopsies may be taken in three ways:
a. Total excision biopsy is preferred for tumors and ulcers (diagnostic and curative).
b. Elliptical biopsy (containing junctional area of lesion and normal skin).
c. Punch biopsy (the most commonly used method; include no normal skin, as sample is small and may be trimmed in wrong direction!!)
Whichever method used, always include the subcutis. If disease mainly involves subcutaneous fat, must do elliptical biopsies. Do NOT "prepare" (clean, wipe, scrub, etc.) skin in any way prior to biopsy. If clipping is needed, do not clip too close as this removes surface material. Hold clipper blade 1/16 to 1/8 inch above the skin's surface.