Biopsy: skin

• Skin histopathology is a valuable aid to differential and definitive diagnosis of many skin disorders.

• Definitive diagnosis of certain skin diseases.
• Categorization of skin disease.

Disadvantages

• Excisional if lesion small enough, or incisional.
• Most animals require sedation.
• Nasal, facial and footpad lesions: may require short-acting general anesthesia.
• Must be obtained early in course of disease before chronic inflammatory changes occur.
• Exercise caution if:
  • Bleeding disorders or concurrent medication, eg aspirin or anticoagulants, affecting bleeding.
  • Immunosuppressed animals: rare (may be wound healing problem).
  • Local anesthesia: injecting lignocaine Lidocaine with adrenaline near extremities and into patients with circulatory disorders (maximum 1ml of 2% lignocaine/5kg body weight).
• Select primary lesions if possible.

• Artifacts may cause difficulty in interpretation.
• Representative tissue must be submitted.

Preparation

• 5-20 minutes.

Procedure

• 5-20 minutes.

Criteria for choosing test

• Primary lesions.
• Deep lesions.
• Masses or any possible neoplastic lesions.
• Non-healing lesions.
• Conditions failing to respond to therapy (generally within 3 weeks).
• Unusual or atypical dermatoses.
• Conditions suspected which require therapy which may be expensive, of extended duration or hazardous.
• Dermatosis diagnosed by biopsy, eg immune-mediated skin disease .
  Stop topical or systemic glucocorticoid therapy 2-4 weeks before biopsy.If secondary bacterial pyoderma Bacterial skin disease: overview, administer course of systemic antibiotic therapy before biopsy.

Risk assessment

• Sedation or general anesthesia: routine checks
• If known bleeding disorder: caution.

Other involvement

• Veterinary specialist dermatohistopathologist.

Minimum equipment

• Sterile surgical instruments.

Minimum consumables

• Local anesthetic (1-2% lidocaine Lidocaine) preferably without adrenaline.
  Adrenaline can cause histological artifacts in vasculature.
• 25G needles and syringe.
• Scalpel blade or 4-8mm biopsy punch.
• Suture material.
• Small-toothed forceps or 25g needle.
• Wooden tongue depressors or cardboard.
• 10% neutral buffered formalin.
• Special fixative may be required eg Michel's fixature for immunofluorescence testing.

• Select primary lesions (macules, papules, pustules, vesicles, bullae, nodule and tumors).
• Avoid excoriated sites.
• Clip hair very gently, if necessary.
  Do not cleanse or prepare site in any way.

Step 1 - Select site

• For wedge biopsy - biopsy at junction of normal and abnormal skin; ensure wedge orientation is correct.
  The lesion should be at one pole of ellipse and normal tissue at other because samples are cut longitudinally during processing.
• For punch biopsy sample lesional tissue and 'normal' skin separately.

Step 2 - Marking site

• Mark site of biopsy with indelible marker to prevent inadvertent sampling of non-blocked areas.
• Place 4 dots equidistant from site or encircle site.

Step 3 - Local anesthesia

• Using a syringe with 25G needle, introduce lidocaine 2% into subcutaneous tissue directly beneath lesion.

Step 4 -

• For minimal patient discomfort, gently reposition the needle (without removing it) to deposit anesthetic in fan-like pattern.

Step 5 -

• Wait 5-8 minutes before performing biopsy.

Step 1 - Punch biopsy

• Place punch directly over lesion to be sampled.
• Rotate gently in one direction while exerting gentle downwards pressure.
  Do not rotate back and forth because this may cause sample damage by shearing forces.
• Continue until punch 'drops' into subcutaneous tissue   .
• Use 25g needle to raise sample from site.
• Use scalpel blade to cut sample plug from small pedicle of subcutaneous tissue and fat to which it is attached.

Step 2 - Wedge biopsy

• Excise ellipse of tissue using a surgical blade.
• Do not exceed 2cm in width or length because larger specimens may not fix adequately.
• Grasp one end with forceps when freeing section from subcutaneous tissues.

Step 3 - Specimen preservation

• Gently remove specimen with a pair of small toothed forceps or mosquito hemostats.
• Grasp only by hair stubble, subcutaneous fat or edge of dermal-epidermal junction.
  Excessive manipulation can make specimen useless.
• Blot excess blood.
• Place subcutaneous side of biopsy on small piece of tongue depressor or cardboard to prevent curling during fixation (wedge biopsy only)     .
• Allow to stand for 30-60 seconds.
• Place in 10% neutral buffered formalin as soon as biopsy has adhered, ensuring volume of fixative is at least x10 volume of sample.
• Allow specimen to fix for 24 hours.
• Special procedure if suspect mycobacterial skin disease: collect biopsy, cut into three pieces etc.

Step 1 - Suture biopsy site

• Standard skin suturing technique.

Step 2 - End sample

• Use specialist veterinary dermatohistopathologist.
• Include details of history (including medication), clinical appearance, sites biopsied and differential diagnosis.

Antimicrobial therapy

• Only if immunosuppressed animal.

• Rare.
• Hemorrhage in animals with bleeding disorders, taking aspirin or anticoagulants (stop 1-2 weeks before biopsy).
• Delayed wound healing in immunosuppressed patients + those on corticosteroids.
• Lidocaine toxicity particularly if injected near extremities and into patients with circulatory disorders (maximum 1ml of 2% lidocaine/5kg body weight).

Poor biopsy sampling

• Improper site selection.
• Improper preparation, eg surgical scrubbing.
• Intradermal local anesthetic injection.
• Shearing of specimen by blunt punch or poor technique.
• Squeeze artifacts due to crushing with forceps.
• Hemorrhage due to inadequate blotting can obscure pathologist's view of tissue.
• Dehydration due to drying in air: specimen must be placed in formalin within 1-2 minutes.
• Shrinkage, curling and folding due to failure to use wooden or cardboard splints.
• Freezing.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Noxon J O (1995) Diagnostic procedures in feline dermatology. Vet Clin North Am Small Anim Pract 25 (4), 779-99 PubMed.

Other sources of information

• Ihrke P J (1996) Bacterial Skin Disease in the Dog - a Guide to Canine Pyoderma. Veterinary Learning Systems. pp 59-61. (Biopsy technique with special reference to pyoderma.)
• Ogilvie G K & Moore A S (1995) Managing the veterinary cancer patient: A practice manual. Veterinary learning systems pp6-8.
• Moriello K A & Mason I S (1995) Eds Handbook of Small Animal Dermatology. 1st edn. Oxford: Pergamon. pp 31-33. (Step by step procedure with photographs.)
• Muller G H et al (1995) Muller and Kirk's Small Animal Dermatology. 5th edn. Philadelphia: W B Saunders. pp 111-118. (Detailed account.)