Introduction
Skin diseases are among the most common problems that animals present to the veterinarian for, and as any practicing veterinarian knows, management and diagnosis of skin diseases can be challenging and complicated.1 The intent of the authors is to present general guidelines and suggestions to help obtain the most diagnostic samples when skin biopsy is determined to be helpful in management of our patients. Teamwork and communication between the clinician and pathologist are important in obtaining the most accurate and useful information to help the patient. It is also important to note that a skin biopsy, like many other diagnostic tests, is not always going to provide a definitive diagnosis, but it is a very powerful diagnostic test. If a definitive diagnosis is not obtained, the information obtained can often be used to make meaningful changes in treatment and rule out other clinical differentials. Since disease conditions change over time, in some conditions, this powerful diagnostic test may need to be repeated. Just as with clinical pathology and other diagnostic tests, the skin biopsy sample represents a snapshot in time. Important diagnoses can be missed if incorrect samples are obtained, if the samples were obtained too early in the course of the disease, or if the skin biopsy is not repeated because a previously performed skin biopsy, often months or years previously, did not yield a diagnosis, so it is assumed that repeating the test will have the same results. The goal of the authors is that the following suggestions and tips will improve patient care, strengthen the patient-client-veterinarian bond, and improve communication and teamwork within the medical and diagnostic teams.
When should a practitioner collect skin biopsies?
In many cases, a biopsy might not provide a definitive diagnosis but may guide the practitioner on the most appropriate treatment of choice or additional diagnostics tests to be run to rule in/out certain conditions. Circumstances and common skin lesions that should be biopsied include the following1–4:
Any case that is likely to have the major diseases most readily diagnosed by biopsy.
A dermatosis that is not responding to presumptively appropriate therapy.
Any dermatosis that, in the experience of the clinician, is unusual or appears serious.
All nodular dermatosis, including neoplastic or suspected neoplastic conditions.
Pustular and bullous lesions.
Alopecic disorders not caused by grooming or pruritus.
Any suspected condition for which the therapy is expensive, dangerous, or considerably time consuming to necessitate a definitive diagnosis before beginning treatment.
However, not all skin lesions presented by a patient need to be biopsied. For instance, the collection of skin biopsies from patients with hypersensitivities and allergic skin diseases can be of low diagnostic value, as the pathologist is unable to differentiate between the various causes responsible for skin allergies in animals. A biopsy should not replace other dermatologic clinical work-up methods, such as deep skin scrapes. In certain cases, a diagnosis may be obtained with a biopsy; however, other diagnostic methods may be less invasive and have higher success in obtaining the diagnosis. A common example is dermatophytosis, in which cultures and/or polymerase chain reaction (PCR) have much higher sensitivity.5
Factors to consider before biopsy
Under optimal conditions, oral corticosteroids and immunomodulatory therapies should be discontinued for 2 to 3 weeks prior to biopsy, and injectable, long-lasting corticosteroids should be discontinued for 6 to 8 weeks if possible.1 Although these medications can greatly affect the microscopic lesions in skin biopsy samples, sometimes the condition of the patient will not allow withdrawal periods for such long periods. Prior to collecting skin biopsies in these cases, a discussion with the pathologist or referral may be indicated. If medications were not appropriately withdrawn prior to the collection of skin biopsies, this information should be included in the clinical history together with the submission of specimens.
Secondary infections can obscure the histopathologic features of the underlying disease, and it is crucial to try and clear secondary infections with appropriate therapy before biopsies are performed.1 If that is not possible, practitioners need to keep in mind that rebiopsy may be necessary in the future.
Factors that help obtain the most information from skin biopsy samples
It is always recommended to submit your biopsy samples to a veterinary dermatopathologist.3 Dermatopathologists are individuals with special training in skin diseases and often formal (or informal) training in this area. In general, the practitioner will obtain more useful information for the patient.
We strongly recommend submitting multiple skin biopsies. Most conditions have early, fully developed, and late changes so selecting a variety of lesions will maximize results. Obtaining histologic evaluation of the full spectrum of lesions, so the pathologist can see the evolution of lesions, will provide much more information than just a single lesion.6 The likelihood of obtaining a definitive diagnosis or obtaining quality information to guide additional tests or treatment will be increased with multiple biopsies. The pathologist can only diagnose and interpret what they can see. The practitioner sees the whole patient, and the pathologist is seeing a very small piece of the patient, so more tissue will always provide more information about the patient. In general, we recommend at least 3 to 4 punch biopsies representative of different lesions be collected from a patient.1
A complete clinical history needs to be submitted, particularly with dermatopathology. There are some clinicians who believe that providing a history will negatively influence the pathologist, and never submit a history for skin or any other tissue. Not submitting a clinical history will greatly decrease the information that is received from the pathologist. As previously said, pathologists only get to see a very small portion of the patient in contrast to the clinician who sees the entire patient. The signalment, distribution, duration, progression, appearance of the lesions, medical history, medication history, etc, are very important for dermatopathology. It is crucial to include a list of differential diagnosis. Make sure to include on the submission form the sites where biopsies were collected. Most pathologists initially scan a slide before looking at the history to develop an opinion and then read the history. Additional stains, levels, etc, may be ordered if the initial impression does not match with the clinical history and signalment. Describing the pathology and interpreting it in skin submissions without a clinical history are analogous to a patient being dropped off for an exam without a history or an owner that cannot answer any questions regarding clinical signs, etc. This happens all the time, and we do our best with what we have; however, the amount of information the pathologist can provide to help the management of the patient is going to be far less.
If obtained, clinical photographs should be included with the specimen submission. Photos can significantly help the interpretation of the lesions as they allow the pathologist to correlate the microscopic findings with the gross lesions and allow them to see more of the whole patient. In some cases, the photographs may not fit with the microscopic lesions, and these discordant findings may lead to decisions to order special histochemical stains, additional tissue levels, etc. Discordant clinical and microscopic lesions most commonly occur when suboptimal samples are submitted, and if additional levels, special stains, etc, are not helpful, the pathologist and clinician should discuss the case. This can also be helpful to rule-out human error in submission or processing of the tissues.
Biopsy Selection and Technique
Biopsy selection is often considered an art, and experience with different skin conditions will help clinicians pick lesions and subtle changes that they suspect will show the diagnostic changes.1 Knowing the difference between primary and secondary lesions is critical. Primary lesions should be given preference and be biopsied first. These include macules, papules, pustules, vesicles, bullae, nodules, plaques, bulla, and wheals (Figure 1). Secondary lesions should be included with primary lesions or if primary lesions are not present. Secondary changes include crusts, epidermal collarettes, scars, excoriation, erosion, ulcers, fissures, lichenification, and calluses (Figure 2).1,2,6 In patients suspected to have pemphigus foliaceus, crusts may be helpful and diagnostic, particularly in chronic cases where intact pustules are no longer seen.7 Certain lesions may be either primary or secondary (alopecia, scale, crust, follicular casts, comedones, and pigmentary abnormalities). References1,4,8 with additional clinical photographs of primary and secondary lesions are provided. When in doubt on what to biopsy, please discuss with the pathologist prior to biopsy or consider referral to a dermatologist.
Primary lesions should be given preference and be biopsied first. A—Papules in the concave pinna of a dog. B—Bullae and vesicles in the oral cavity of a dog. C—Dermal nodules with draining tracts in a dog. D—Nodules with exudation of suppurative inflammation on the dorsum of a dog. E—Nodular and ulcerative lesions on the dorsal muzzle of a dog. F—Plaques on the ventral abdomen of a cat. G—Wheals on the ventral abdomen of a dog.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Primary lesions should be given preference and be biopsied first. A—Papules in the concave pinna of a dog. B—Bullae and vesicles in the oral cavity of a dog. C—Dermal nodules with draining tracts in a dog. D—Nodules with exudation of suppurative inflammation on the dorsum of a dog. E—Nodular and ulcerative lesions on the dorsal muzzle of a dog. F—Plaques on the ventral abdomen of a cat. G—Wheals on the ventral abdomen of a dog.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Primary lesions should be given preference and be biopsied first. A—Papules in the concave pinna of a dog. B—Bullae and vesicles in the oral cavity of a dog. C—Dermal nodules with draining tracts in a dog. D—Nodules with exudation of suppurative inflammation on the dorsum of a dog. E—Nodular and ulcerative lesions on the dorsal muzzle of a dog. F—Plaques on the ventral abdomen of a cat. G—Wheals on the ventral abdomen of a dog.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Secondary lesions. A—Ruptured pustules and crusts in the dorsum of a dog. B—Large epidermal collarettes in the trunk of a dog. C—Erosions and ulcers on the nose and periocular region of a dog. D—Callus on the left elbow of a dog. E—Scar and alopecia in the dorsum of a dog. F—Scales and alopecia on the trunk of a dog.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Secondary lesions. A—Ruptured pustules and crusts in the dorsum of a dog. B—Large epidermal collarettes in the trunk of a dog. C—Erosions and ulcers on the nose and periocular region of a dog. D—Callus on the left elbow of a dog. E—Scar and alopecia in the dorsum of a dog. F—Scales and alopecia on the trunk of a dog.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Secondary lesions. A—Ruptured pustules and crusts in the dorsum of a dog. B—Large epidermal collarettes in the trunk of a dog. C—Erosions and ulcers on the nose and periocular region of a dog. D—Callus on the left elbow of a dog. E—Scar and alopecia in the dorsum of a dog. F—Scales and alopecia on the trunk of a dog.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
It is important for practitioners to be familiar with the pathogenesis of common skin diseases and what the clinical (and possibly microscopic) lesions are for the suspected condition, as well as consider possible differentials prior to biopsy. This information will help determine which lesions to biopsy. If the distribution of the lesions is unusual for the suspected disease, biopsy specimens should be obtained from the unusual as well as the more common areas. Fluid-filled lesions such as vesicles and pustules are fragile and transient and should be biopsied as soon as possible. This may require communication with the client or short hospitalization with monitoring for the lesions to appear.1
How to biopsy
In general, a 6- or 8-mm punch will provide an adequate specimen in most cases (Figure 3). The 4-mm punches are reserved for more difficult sites such as periocular, pinna, nasal planum, and footpads of small dogs and cats.1 The location of the lesions and the patient’s behavior will determine if sedation and local anesthesia or general anesthesia will be required to obtain quality samples.3
Punch biopsy procedure. A—Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center. The hair at the site can be trimmed with scissors above areas where there is abundant scaling and crusting. The practitioner must be careful to avoid removing surface keratin. B—The biopsy punch should be rotated in one direction until it sinks into the subcutaneous tissue to avoid shearing of tissue. C—Great care should be taken in handling the tissue with instruments and small-caliber needles, Adson tissue forceps, iris or small curved scissors, small-caliber needle, or tiny mosquito hemostatic should be used over Adson tissue forceps to support the plug of tissue from underneath to not crush the tissue or introduce artifact. D—The tissue free from the underside should be cut with iris scissors as rough tissue handling can significantly damage small samples and induce artifact that can be difficult to interpret. E and F—Punch biopsy sample sites may be closed with cruciate or simple interrupted sutures.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Punch biopsy procedure. A—Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center. The hair at the site can be trimmed with scissors above areas where there is abundant scaling and crusting. The practitioner must be careful to avoid removing surface keratin. B—The biopsy punch should be rotated in one direction until it sinks into the subcutaneous tissue to avoid shearing of tissue. C—Great care should be taken in handling the tissue with instruments and small-caliber needles, Adson tissue forceps, iris or small curved scissors, small-caliber needle, or tiny mosquito hemostatic should be used over Adson tissue forceps to support the plug of tissue from underneath to not crush the tissue or introduce artifact. D—The tissue free from the underside should be cut with iris scissors as rough tissue handling can significantly damage small samples and induce artifact that can be difficult to interpret. E and F—Punch biopsy sample sites may be closed with cruciate or simple interrupted sutures.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Punch biopsy procedure. A—Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center. The hair at the site can be trimmed with scissors above areas where there is abundant scaling and crusting. The practitioner must be careful to avoid removing surface keratin. B—The biopsy punch should be rotated in one direction until it sinks into the subcutaneous tissue to avoid shearing of tissue. C—Great care should be taken in handling the tissue with instruments and small-caliber needles, Adson tissue forceps, iris or small curved scissors, small-caliber needle, or tiny mosquito hemostatic should be used over Adson tissue forceps to support the plug of tissue from underneath to not crush the tissue or introduce artifact. D—The tissue free from the underside should be cut with iris scissors as rough tissue handling can significantly damage small samples and induce artifact that can be difficult to interpret. E and F—Punch biopsy sample sites may be closed with cruciate or simple interrupted sutures.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center and the lesion needs to incorporate most of the tissue sample (Figures 3 and 4). Do not include a lot of normal tissue; otherwise, the lesion may not be cut into appropriately. The clinician should realize that after formalin fixation erythema and color changes are often not detectable by the person who sections the sample and small lesions such as papules and pustules may not be seen, so the location of the lesions in the center of the sample helps avoid this problem.1
Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center and the lesion needs to incorporate most of the tissue sample.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center and the lesion needs to incorporate most of the tissue sample.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
Primary lesions should be located in the center of the punch as the lab bisects punch biopsies through the center and the lesion needs to incorporate most of the tissue sample.
Citation: Journal of the American Veterinary Medical Association 261, S1; 10.2460/javma.22.12.0586
If transitional areas between lesional and nonlesional skin need to be submitted, it is best to use an elliptical biopsy. A common example is blistering disorders. The roof of a blister (bullae) may be lost during submission or processing when punch biopsies are collected, and the diagnosis may be missed in these cases.2,6
With alopecic disorders, at a minimum 3 samples should be submitted. Two samples from the most alopecic area and another sample from normal-haired skin. Marginal biopsy samples from alopecic and normal-haired skin are not recommended and should be avoided.7 This helps the pathologist as there is marked variation in what is normal for the individual patient with all the different breed variations, seasonality, etc. This allows examination of what is normal for that particular patient to compare to the abnormal. If a normal sample is submitted, make sure to include this information in the submission form.
In subcutaneous nodular disorders, including neoplastic conditions, a punch biopsy may be too superficial and may miss the actual lesion. In these cases, a wedge biopsy will generally be more successful.1,6 Another alternative is to use a “double punch,” although it will provide less tissue than a wedge biopsy sample. “Double punches” are obtained by using the punch biopsy instrument to obtain deeper tissue samples at the same location after the first skin punch biopsy is removed.4
Should you prep the biopsy site or not?
In general, biopsy collected for histopathology should not be prepped as it is important to preserve crust and not damage the epidermis. If dealing with a deep nodular disorder, the biopsy site can be prepped to obtain the most aseptic specimen for bacterial and fungal cultures.
The hair at the site can be trimmed with scissors above areas where there is abundant scaling and crusting. The practitioner must be careful to avoid removing surface keratin. The surface should be left untouched, or if absolutely needed, 70% alcohol can be daubed on top. For superficial lesions, never scrub with antiseptics. Wash off (if necessary) with plain water and pat dry. Keep crusts and scales intact, and if these slough off, submit them for histologic evaluation, especially in suspicious cases of pemphigus foliaceus.1,2,4
Local anesthesia 1 to 2 mL of 1 to 2% lidocaine should be injected subcutaneously with a 25-gauge needle. Ring blocks are more appropriate when panniculitis is suspected as an injection into the subcutis/panniculus will result in tissue artifact. Buffering with 8.4% sodium bicarbonate at a 10:1 lidocaine to bicarbonate ratio minimizes sting. Be careful with lidocaine doses injected in small dogs and cats and do not exceed a total dose of 5 mg/kg for dogs and 2.5 mg/kg for cats. Lidocaine may be diluted 1:1 with saline for these small patients. Do not inject the local anesthetic directly into the tissue that will be submitted as this will introduce an artifact. Lidocaine, bicarbonate, and epinephrine inhibit various gram-positive and gram-negative bacteria, mycobacteria, and fungi. In cases where tissue is being obtained for culture, a ring block, regional anesthesia, or general anesthesia is more appropriate.1
The biopsy punch should be rotated in one direction until you feel it sink into the subcutaneous tissue to avoid shearing of tissue (Figure 3). Take great care in handling the tissue with instruments and use small-caliber needles, Adson tissue forceps, iris, or small curved scissors, small-caliber needle, or tiny mosquito hemostatic over Adson tissue forceps to support the plug of tissue from underneath to not crush the tissue or introduce artifact (Figure 3). Cut the tissue free from the underside with iris scissors as rough tissue handling can significantly damage small samples and induce artifact that can be difficult to interpret (Figure 3). Please do not use electrocautery or laser for obtaining skin punch biopsy samples. Significant tissue damage and marked artifacts will occur, greatly reducing the amount of tissue that can be evaluated and hindering the diagnostic quality. Punch biopsy sample sites may be closed with cruciate, simple interrupted, or mattress sutures dependent upon the location and clinician preference (Figure 3).1,4
Excisional biopsy with a scalpel is often indicated for larger lesions, vesicles, bullae, and pustules in which the twisting action of the punch biopsy instrument may rupture these lesions and for suspected cases of panniculitis.1,2,6 Aim to orient the ellipse along the way the hair grows so the follicles can be examined longitudinally (in the lab, samples are sectioned the way the hair grows). Place the biopsy “epidermis up” on cardboard or a piece of tongue depressor. For margins of the pinna and footpad, as well as deep lesions, a wedge biopsy can be used.
Shave biopsy can be helpful when biopsying the tips or margins of the pinnae to avoid permanent cosmetic changes with loss of tissue. There are several shave biopsy blade options available from human and veterinary supply companies that are cost effective and are designed with safety in mind. Alternatively, a No. 15 scalpel blade may be used. To perform a shave biopsy, the blade is held parallel to the skin surface distal or medial to the lesion. Shave to the level of the cartilage, but do not include the cartilage, and advance to blade away from you to the periphery of the lesion. Shave biopsy samples should be placed on a section of tongue depressor or piece of cardboard to avoid curling as these samples are quite thin shave biopsy sites are not sutured. Pressure with or without epinephrine can be applied for hemostasis. Some will apply a topical antibiotic for several days until the biopsy site heals.9
All samples should be placed in 10% neutral buffered formalin immediately after the biopsy to prevent autolysis, which occurs quickly, and can affect histologic interpretation. To prevent freeze artifact when mailing samples during cold temperatures, allow 12 hours of formalin fixation prior to shipping the samples or add 95% ethyl alcohol as 10% of the fixative volume.1
How to interpret the histopathology report
The pathology report will most often include the histologic description of the slide, a morphologic diagnosis, and a comments section. Pathologists use proper terminology to describe histologic changes involving the skin, with comprehensive glossaries found in reference books.1,10 Some labs may offer the histologic description for an extra fee, and it is recommended to always request a histologic description be included with each submission. In the morphologic diagnosis section, pathologists will summarize their findings including the main pattern observed in the histologic specimens. It is important for clinicians to understand the different histopathologic patterns of skin lesions. This information should be used by clinicians and pathologists to confirm a diagnosis and to compile a list of differentials within each pattern. Even if a diagnosis cannot be confirmed, knowing the histologic pattern in skin lesions should help the practitioner to select the most appropriate treatment choices for patients. If a differential list was provided by the clinician, the pathologist will often provide comments explaining why certain differentials are plausible and fit with the histologic patterns observed in the examined sections or reasons why differentials were excluded/ruled out.
Most pathologists work in a laboratory and are not in the practice of treating patients. Thus, with a few exceptions, the pathologist may not be a reliable source to develop a treatment plan for patients. The best approach to take in patients presented with severe lesions and refractory to treatment is to refer or discuss the case with a veterinary dermatologist. Telemedicine with virtual consults may be an option if a specialty clinic or hospital is not available nearby.
For cases suspected to be due to infectious causes, communicate with the pathologist, and if abundant inflammation is observed, request the pathologist to run special stains if those were not initially done. Keep in mind special stains have a low sensitivity to identify infectious organisms in tissues. Thus, cases suspected to be due to an infectious cause should always be accompanied by the submission of fresh deep biopsy samples for bacterial and fungal culture. These can often be collected at the same time as biopsies submitted in formalin for histopathology; however, they need to be submitted in saline and cannot be fixed in formalin. If there are financial concerns, the practitioner can check with the lab if samples for culture can be held and only processed after a histologic evaluation is completed and if recommended by the pathologist.
If the lesions observed clinically are not included in the histopathology report, communicate with the pathologist, as the lesions may have been missed on the initial sectioning, and it may be necessary to evaluate deeper levels of the block. If the interpretation provided by the pathologists does not fit the clinical history, practitioners should contact the pathologist to better discuss the case and to consider other differentials. In difficult cases, it is important for both practitioners and pathologists to keep close communication to provide the highest quality of care for patients.
Final Remarks
Lesion recognition and skin biopsy selection and technique are skills that take years of practice to perfect. As with all aspects of the practice of veterinary medicine, there is always room for improvement and lifelong learning. The authors hope that this review provides some helpful tips for clinicians and pathologists at all stages of their careers and will help us all enhance patient care through communication and teamwork within the medical and diagnostic teams.
Acknowledgments
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript.
The authors declare that there were no conflicts of interest. Dr. Marsella served as Guest Editor for this Journal of the American Veterinary Medical Association (JAVMA) Supplemental Issue. She declares that she had no role in the editorial direction of this manuscript.
We acknowledge Drs. Kalie Marshall and Nathalia Gil for assistance with the biopsy procedure.
References
- 1.↑
Miller WH, Griffin CE, Campbell KL. Diagnostic methods. In: Miller WH, Griffin CE, Campbell KL, eds. Muller and Kirk’s Small Animal Dermatology. 7th ed. Elsevier Mosby; 2013:57–107.
- 2.↑
Bettenay SV, Hargis AM. Biopsy collection: why, when, where and how. In: Practical Veterinary Dermatopathology. Teton NewMedia; 2006:1–20.
- 3.↑
Hnilica K, Patterson A. Diagnostic techniques. In: Small Animal Dermatology: a Colour Atlas and Therapeutic GuideI. 4th ed. Elsevier Saunders; 2016:30–44.
- 4.↑
Logas D. When, where, and how to biopsy skin. In: Diagnostics and Therapy in Veterinary Dermatology. Wiley Blackwell; 2022:33–38.
- 5.↑
Moriello KA, Coyner K, Paterson S, Mignon B. Diagnosis and treatment of dermatophytosis in dogs and cats. Vet Dermatol. 2017;28(3):266-e38. doi:10.1111/vde.12440
- 6.↑
Dunstan RW, Mauldin EA, Davenport GM, Credille KM. A guide to taking skin biopsies: a pathologist’s perspective. In: Campbell KL, ed. Small Animal Dermatology Secrets. Hanley and Belfus; 2004:34–42.
- 7.↑
Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat Clinical and Histopathologic Diagnosis. 2nd ed. Blackwell Science; 2005.
- 8.↑
Welle M, Linder K. The integument. In: Zachary JW, ed. Pathologic Basis of Veterinary Disease. 7th ed. Elsevier; 2022:1095–1262.
- 9.↑
Fadok V. Biopsying places you don’t want to biopsy: footpads, claws, ears, and noses. Veterinary Information Network (VIN). Accessed December 23, 2022. http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=MEDFAQ&Category=1477&PID=52461&O=VIN
- 10.↑
Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy & Palmer’s Pathology of Domestic Animals. Vol 1. Elsevier; 2016:509–736.e1.
