Everything You Always Wanted To Know About Skin Biopsy in Small Animals But Were Afraid To Ask
Department of Pathology, School of Veterinary Medicine and Animal Science, University of Sao Paulo
The skin is the largest, most visible and complex organ in which precisely regulated cellular and molecular interactions govern many crucial responses to the environment. We know that skin is composed of a number of interdependent cell types and structures that work toward a common protective goal.
Factors affecting the delicate homeostasis that exists among skin cells and structures may result in conditions as diverse as wrinkles and hair loss, blisters and pigmentation disorders, and even life-threatening malignant neoplasm and disorders of immune regulations. In addition, the skin is synergistic with internal organ systems and thus reflects pathologic processes that are either primary elsewhere or share with other tissues.
Dermatologic disorders are among the most common reasons clients seek professional help from veterinarians. Nowadays, it is also an important medical specialty in animal medicine. Many skin diseases of dogs and cats are manageable but not curable. The main goal behind these few words is to help veterinarian clinics and pathologists make right decisions when attempting to diagnosis or interpret histological lesions in biopsies.
Skin Biopsy: Indications and Getting a Good Biopsy Sampling
The lesions and symptoms of skin disease are external and potentially visible to the owner and practitioner. Knowledge of clinical appearance of skin problems, distribution of lesions, and correlation between the gross and histological lesions is critical in formulating differential and final diagnoses. The clinical lesions represent the gross lesions and are examined by the practitioner who may have the ability to recognize clinical lesion morphology and translate that information to the pathologist. Skin biopsy is one of the most important tools in dermatology. When the clinician and pathologist truly work together, the skin biopsy can represent the dermatologic diagnosis in the most cases. Biopsy sampling is indicated when:
1. The clinical diagnosis may be confirmed before starting the therapy, in cases of the therapy for skin disorder is expensive or associated with side effects, sufficiently time consuming
2. A nodular, ulcer, or nonhealing wound
3. All obviously neoplastic or suspected neoplastic lesions
4. Skin lesions develop suddenly, are severe, or are unusual
5. Lesions develop during the course of therapy or a dermatosis is not responding to apparently rational therapy
6. Vesicular and pustular dermatosis
7. Any case that is likely to have major diseases that are most diagnosed by biopsy (e.g., sebaceous adenitis, dermatomyositis, immune-mediated skin disease)
We may consider that skin biopsy should be performed within 3 weeks for any dermatosis that is not responding to what appears to be appropriate therapy. It is also relevant to know that anti-inflammatory agents can dramatically affect the histologic appearance of many dermatoses. The administration of such medications, especially glucocorticoids, should be stopped for 2 to 3 weeks before biopsy. The histopathologic changes caused by secondary bacterial pyoderma often obliterate the histopathologic features of any concurrent dermatoses. It is imperative to eliminate these secondary infections with appropriate systemic antibiotic therapy before biopsies are performed.
What to Biopsy: Site Selection
Multiple biopsies should be taken from several sites, illustrative of the whole range of clinical lesions.
Early or full developed nontreated primary lesions, such as macules, papules, pustules, nodules, neoplasm, vesicles, and wheals, which represent the uncomplicated disease process, should be selected wherever possible. Secondary lesions, such as scales, crusts, ulcers, comedones, or scars can be sampled and evaluated in some cases. These secondary lesions can be diagnostic or contribute to the diagnosis when multiple cutaneous sites are selected for biopsy.
How to Biopsy: Instruments and Methods
Biopsies are performed gently, simply and quickly with local anesthesia. The general equipment needed for most cases are: two percent lidocaine; a selection of punch biopsies of different sizes; small curved scissors; Adson thumb forceps; formalin vials; needles and suture material; needles holders; wooden tongue depressors, and gauze pads.
Lesions should not be surgically prepared (e.g., scrubbed, clipped).If necessary, very gently clip or scissor the hair. Biopsies should be free of squash, cauterization or other operator that may induce artifact.
It is recommended six or eight mm biopsy punch. Four millimeter punches should be used only if larger biopsies are too damaging (i.e., footpad, periocular skin, nasal planum). Incisional or excisional (entire lesion) biopsy with scalpel is often indicated for larger lesions; for vesicles, bullae, and pustules; and for suspected disease of the subcutaneous fat.
For alopecic condition you may collect samples from most alopecic areas; draw a line on the sample in the direction of the hair coat; for ulcers or depigmenting lesions the junction is important and you may use incisional or excisional method or use 8-mm biopsy punch instrument, and draw a line on the sample perpendicular to the junction between lesion and normal skin. You should include the crusts. Digital amputation can be required for the diagnosis of claw bed lesions. For lesions suspected of being invasive tumors, complete excision of the mass, including a 3-cm margin of clinical normal skin around the borders is recommended.
After skin biopsy, the samples should be manipulated gently and fix in 10% buffered formalin with 10 times the volume of formalin for the volume of samples. To prevent warping in the fixative, thin excisional biopsy specimens should be attached to a flat object, such as a piece of cardboard or tongue depressor, and permitted to dry for 20 to 30 seconds and then immediately immersed in formalin.
The last critical consideration is to send the sample with full signalment, complete and accurate history and list of rule-outs or differential diagnoses to the histopathologic laboratory. Dermatohistopathology: what should I know? The clinician and the pathologist are diagnostic team, and an accurate diagnosis is dependent of both members of the team do their parts. In this context, it is important to understand how the pathologist deal with the biopsy sample submitted for microscopic exam.
First of all, it is imperative to know that dermatohistopathology has a specialized vocabulary. Some important and reference books provide in details all terms which has been used by pathologist.
Looking at the Histological Specimen
The pathologist starts to look at the biopsy before he read the history. At the low magnification, the scanning ensures that all biopsies on the slide had been examined and the pathologist receives the impression of the distribution of the lesions with each piece. At this moment, in the most cases it is possible to decide whether the lesion is inflammatory or neoplastic.
If it is inflammatory, the pathologist decides on the major pattern or anatomical target; decide on the predominant inflammatory cell and finally write a full description of the microscopic lesions. If it is necessary, he will ask for complementary procedure such as special stain, aseptically collecting a tissue sample for microbiologic culture.
If it is neoplastic, the pathologist decides whether it is growing in a pattern or making a product that resembles any element of normal skin. If it gives him no immediate clues as to origin, he may decide whether it is epithelial or non-epithelial tumor reading and studying about the tumor to point the direction or he will consider immunostaining procedures.
Providing an Interpretation and Comment
After the pathologist make a morphological diagnosis and, if possible, an aetiological diagnosis, he returns to the clinical history, signalment and description of clinical signs to interpret his microscopic findings. At this time, the pathologist combines the impressions that the microscopic examination have given him with the information provided by the practitioner.
The specialized literature available and the experience allowed the pathologist to provide a comment what is in general the most part of the report. The pathologist can explain his reservations or difficulties in interpreting the biopsy, give added information about treatment, suggest further investigative procedures and, for tumors, give the know prognosis.
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