Diagnostics and Therapy in Veterinary Dermatology. Группа авторов

Figure 2.7 Ulcerations, draining tracts, and scarring in the inguinal region of a cat with rapid‐growing mycobacteria.

Figure 2.8 Perianal erythema in a dog with food allergy.

Recording Results

      While a complete dermatologic examination is important, much of its value is in its recording. As many students are taught in veterinary school, if something isn’t documented, it didn’t happen. Too often the details of the exam don’t make their way into the medical record, which can make it difficult to reassess patients and their response to therapy. Additionally, patients frequently see multiple doctors within a practice. The more information that is provided to the next veterinarian, the better they will be able to adjust therapeutic and diagnostic plans. Details such as the percentage of stenosis of an inflamed horizontal ear canal, tail head distribution of a bacterial folliculitis, or location and size of perianal fistulae can help the next clinician, or even someone several months or years in the future.

Figure 2.9 Dog with chronic solar dermatitis. Multifocal areas of erythema and erosions with purulent exudate. The white‐skinned areas feel thickened and rough, while the black‐skinned areas palpate normally.

      Much like the exam itself, there are different options for recording dermatologic findings. Many medical record systems include body map images of animals that can be marked to denote the location of different lesions. The body map can provide a quick way to assess lesion distribution and help to formulate differential diagnoses. It is also important to include a description of the different lesions, not just their location.

      Another option for recording dermatologic exam findings is through written descriptions. These can be particularly helpful in complex cases with a variety of lesions. Finally, today’s electronic systems make it relatively easy to include photographs as part of the patient’s medical record. Pictures can enable a more reliable measure of improvement and can make it easier for new doctors to manage a case that has previously been treated.

3 New Diagnostic Tools and Tests for Dermatology

       Amelia White

       KEY POINTS

       Traditional in‐house dermatologic diagnostics require the technical expertise of the technician or clinician to provide accurate results.

       New laboratory diagnostic techniques can give more accurate information without the need for in‐house expertise.

       New diagnostic techniques can provide quicker results, but may be more costly.

       If possible use laboratories that have independent studies verifying the specificity, sensitivity, and accuracy of their tests.

The Importance of Diagnostic Investigations in Dermatology

      Changes in the skin and hair coat of animals frequently signal the presence of a primary disease process. These primary conditions create inflammation and changes in the protective skin barrier function. Alteration of the normal mechanisms maintaining cutaneous microbial homeostasis permits bacteria and fungi residing here to flourish. It is important to consider these secondary infections when diagnosing and treating dermatologic conditions, especially because they complicate the diagnosis of the primary disease. Oftentimes, these secondary diseases must be treated prior to further investigation of the primary disease process. Utilization of multiple diagnostic tools in these cases is common because many dermatologic conditions, both primary and secondary, visually appear identical.

      Traditional diagnostic procedures continue to provide effective and reliable methods of achieving the correct dermatologic diagnosis. These include otic and skin cytology, fine needle aspiration, skin scraping, trichography (hair plucking), diascopy (a test performed by applying pressure to the skin with a glass slide to observe for blanching), Wood's lamp examination, tissue and hair cultures, and histopathology. These diagnostics have many benefits including affordability, low technical complexity, and easy accessibility. However, results are largely dependent on technical skill, correct lesion selection, and appropriate sample size.

      More recently, a transition toward more expensive, rapid, and sensitive testing methodologies using molecular diagnostics has begun. Molecular diagnostic testing uses many different techniques to study the genetic variations in biologic markers found in individual genomes and proteomes. Techniques such as polymerase chain reaction (PCR) or enzyme‐linked immunosorbent assay (ELISA) allow for the detection of microbial DNA from a small sample of skin, even if fungal and bacterial cultures from the same skin were negative.

Molecular diagnostics provide insight into how an individual organism expresses its genetic code, which can dramatically enhance our knowledge of why and how diseases occur. Comparing the genetic code alterations between diseased and normal animals provides a deeper understanding of the pathophysiology of many primary dermatologic diseases. Similarly, assessing changes within an infectious organism's genome before and after antimicrobial exposure improves our understanding of mechanisms of resistance and how selection pressure drives microbial adaptability within the environment. This information can assist us when choosing therapies to target these abnormalities, or when avoiding therapies neutralized by such mutations. Furthermore, new drug development targeting these genetic mutations is paving the way for individualized and safe disease treatments in the future.

      Understanding the genomic variations unique to specific diseases will influence the use of animal models of disease and will contribute to the One Health model of disease recognition and treatment. Rapid and sensitive diagnostic methodology can detect emerging diseases within a population, and track prevalence of diseases over time. Molecular diagnostics are very sensitive techniques for achieving a diagnosis when only a small amount of sample is available; however, the techniques are more complicated and more expensive compared to traditional dermatologic diagnostics. Additional limitations to consider include understanding that the presence of DNA does not prove an organism's viability, and measurement of titers does not indicate active infection. This chapter will focus on the updated diagnostic testing modalities available in veterinary dermatology, particularly molecular diagnostics.

Molecular Diagnostic Tests: How Do They Work and What Is Available?

Not every molecular diagnostic test is created equal. Each test uses a different technique to study a disease or immunologic response, and the data obtained from each test answers different questions. Some tests detect antigens while others detect antibodies. Some tests sequence fragments of DNA or entire genomes to detect the presence of an organism or genetic modification. Refer to Table 3.1 for a list of some of the dermatologic diagnostic tests available today. Also, not every laboratory is created equally. It is important to use reputable laboratories and if possible to be sure the tests they are offering have been verified.

Serology

      Serologic