SKIN BIOPSY
When do I do it?
- Sample any lesion(s) that look unusual or behaves in an unexpected manner
- Consider a skin biopsy if the animal has failed to respond to an empirical course of therapy
- Consider a skin biopsy if the animal is systemically ill
- Biopsy any nodule or non-healing ulcer as these may be neoplastic
- If the potential therapy is potentially dangerous or expensive a diagnosis should be confirmed with histopathology
- To rule out other diagnoses
What can I find?
- Confirm a clinical diagnosis
- Rule out a suspected clinical diagnosis
What do I need?
- Skin punch biopsy (4 mm or 6 mm), thumb forceps, iris scissors, scalpel blade if performing a wedge biopsy, needle holder, suture material, 10% formalin
How do I do it?
- Local anesthesia with sedation and pain management if needed
- Skin is NOT prepped
- If necessary, gently clip the overlying hair
- 1-2% lidocaine or bupivacaine
- Sodium bicarbonate to reduce stinging (1:9)
0.1ml bicarbonate to 0.9ml lidocaine - Epinephrine 1:1,000 into hub of the syringe
0.75–1cc per site, use 25 gauge needle - Recommended safe dose of 2% lidocaine
Dogs:1–1.5 ml/ 4kg
Cats: 0.5–0.75 ml/ 4kg
Dilute 50:50 with saline if larger volume needed - Wait up to 10 minutes for the injection to take effect
Tip
- Take several samples to increase the likelihood of selecting a diagnostic area
- Request a complete microscopic description, not just a diagnosis, as this may help a dermatologist determine the cause of the problem
- Send the samples to a pathologist with an interest in dermatology as they are more likely to be able to match the microscopic changes with a specific etiologic diagnosis
- Provide the pathologist with a list of differential diagnoses and describe the signalment, clinical pattern and lesions seen, and past therapies
abscess
A discrete swelling containing purulent material, typically in the subcutis
alopecia
Absence of hair from areas where it is normally present; may be due to folliculitis, abnormal follicle cycling, or self-trauma
alopecia (“moth-eaten”)
well-circumscribed, circular, patchy to coalescing alopecia, often associated with folliculitis
angioedema
Regional subcutaneous edema
annular
Ring-like arrangement of lesions
atrophy
Thinning of the skin or other tissues
bulla
Fluid-filled elevation of epidermis, >1cm
hemorrhagic bullae
Blood-filled elevation of epidermis, >1cm
comedo
dilated hair follicle filled with keratin, sebum
crust
Dried exudate and keratinous debris on skin surface
cyst
Nodule that is epithelial-lined and contains fluid or solid material.
depigmentation
Extensive loss of pigment
ecchymoses
Patches due to hemorrhage >1cm
epidermal collarettes
Circular scale or crust with erythema, associated with folliculitis or ruptured pustules or vesicles
erosion
Defect in epidermis that does not penetrate basement membrane. Histopathology may be needed to differentiate from ulcer.
erythema
Red appearance of skin due to inflammation, capillary congestion
eschar
Thick crust often related to necrosis, trauma, or thermal/chemical burn
excoriation
Erosions and/or ulcerations due to self-trauma
fissure
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
fistula
Ulcer on skin surface that originates from and is contiguous with tracts extending into deeper, typically subcutaneous tissues
follicular casts
Accumulation of scale adherent to hair shaft
hyperkeratosis
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
hyperpigmentation
Increased melanin in skin, often secondary to inflammation
hypopigmentation
Partial pigment loss
hypotrichosis
Lack of hair due to genetic factors or defects in embryogenesis.
leukoderma
Lack of cutaneous pigment
leukotrichia
Loss of hair pigment
lichenification
Thickening of the epidermis, often due to chronic inflammation resulting in exaggerated texture
macule
Flat lesion associated with color change <1cm
melanosis
Increased melanin in skin, may be secondary to inflammation.
miliary
Multifocal, papular, crusting dermatitis; a descriptive term, not a diagnosis
morbiliform
A erythematous, macular, papular rash; the erythematous macules are typically 2-10 mm in diameter with coalescence to form larger lesions in some areas
nodule
A solid elevation >1cm
onychodystrophy
Abnormal nail morphology due to nail bed infection, inflammation, or trauma; may include: Onychogryphosis, Onychomadesis, Onychorrhexis, Onychoschizia
onychogryphosis
Abnormal claw curvature; secondary to nail bed inflammation or trauma
onychomadesis
Claw sloughing due to nail bed inflammation or trauma
onychorrhexis
Claw fragmentation due to nail bed inflammation or trauma
onychoschizia
Claw splitting due to nail bed inflammation or trauma
papule
Solid elevation in skin ≤1cm
papules
Solid elevation in skin ≤1cm
paronychia
Inflammation of the nail fold
patch
Flat lesion associated with color change >1cm
petechiae
Small erythematous or violaceous lesions due to dermal bleeding
phlebectasia
Venous dilation; most commonly associated with hypercortisolism
plaques
Flat-topped elevation >1cm formed of coalescing papules or dermal infiltration
pustule
Raised epidermal infiltration of pus
reticulated
Net-like arrangement of lesions
scale
Accumulation of loose fragments of stratum corneum
scar
Fibrous tissue replacing damaged cutaneous and/or subcutaneous tissues
serpiginous
Undulating, serpentine (snake-like) arrangement of lesions
telangiectasia
Permanent enlargement of vessels resulting in a red or violet lesion (rare)
ulcer
A defect in epidermis that penetrates the basement membrane. Histopathology may be needed to differentiate from an erosion.
urticaria
Wheals (steep-walled, circumscribed elevation in the skin due to edema ) due to hypersensitivity reaction
vesicle
Fluid-filled elevation of epidermis, <1cm
wheal
Steep-walled, circumscribed elevation in the skin due to edema