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North American Veterinary Dermatology Forum

Clinician's Brief (Capsule)

Dermatology

|November 2015

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Evaluation of Cyclosporine-Sparing Effects of Polyunsaturated Fatty Acids in the Treatment of Canine Atopic Dermatitis  

A randomized, double-blinded, placebo-controlled multicenter trial was conducted to assess the cyclosporine-sparing effect of polyunsaturated fatty acids. Dogs with atopic dermatitis (n = 36) already receiving cyclosporine were given either a combined omega-3/omega-6 fatty acid product or placebo orally for 12 weeks. The dogs were examined monthly by a dermatologist and scored based on the Canine Atopic Dermatitis Extent and Severity Index (CADESI-03). Pruritus, quality of life, overall condition, and coat quality were scored by the owner. Improvements in CADESI-03 or pruritus scores of at least 25% resulted in cyclosporine dosage decreases of about 25%. The median pruritus score was significantly improved in the fatty acid group compared with the placebo group with a significantly greater decrease in cyclosporine dosage. There was no significant difference in CADESI-03 changes between groups. The data suggest that omega-3/omega-6 fatty acid supplementation may have a cyclosporine-sparing effect in atopic dogs. Trial sponsored by Novartis.—Müller M, Linek M, Röthig A, Löwenstein C, Mueller RS

Home-Cooked Diets for Elimination Diet Trials

Home-prepared diets (HPDs) are useful in the management of several diseases of dogs and cats, including food allergies, and some clinicians prefer them over commercial foods as elimination diets. HPDs can be completely customized, which is highly advantageous when managing multiple diseases. Given the recommended length of elimination food trials, it is advisable to provide a complete, balanced diet with all essential nutrients and micronutrients, including vitamins, minerals, essential amino acids, and essential fatty acids. An incomplete HPD for the purpose of an elimination trial may only include a protein and starch or may be an all-meat diet for cats, neither of which is balanced. To formulate an appropriate diet, it is necessary to know 3 things: the energy and nutrient requirements of the animal, the maximum levels of some nutrients, and the nutrient and energy content of the ingredients. There are veterinary industry standards regarding energy and nutrient requirements, maximum levels of nutrients, and published nutrient databases to assess nutrient and energy content of the ingredients. However, a veterinary nutritionist is best-equipped to ensure a home-cooked formulation is safe and appropriate for an elimination trial.—Villaverde C

Comparison of Minocycline & Doxycycline Susceptibilities of Meticillin-Resistant Staphylococcus pseudintermedius Isolates Using Current & Revised Breakpoints

It is believed that the current published Clinical and Laboratory Standards Institute breakpoints for minocycline and doxycycline susceptibility of Staphylococcus pseudintermedius isolates are not appropriate. A new breakpoint for minocycline has been proposed and approved, and 1 for doxycycline has been proposed but not yet approved. Both are 4 dilutions lower than current breakpoints. This study measured the MICs of minocycline and doxycycline in 100 canine meticillin-resistant S pseudintermedius isolates, comparing them against current and revised standard breakpoints. It was found that, using the newly proposed minocycline breakpoint of MIC <0.25 µg/mL, only 31 isolates were susceptible compared with 76 isolates susceptible at the current breakpoint. Similarly, using the newly approved doxycycline breakpoint of MIC <0.125 µg/mL, only 31 isolates were susceptible compared with 36 isolates susceptible at the previous breakpoint. PCR analysis showed that most of the isolates misclassified by the standard breakpoints contained the tetracycline-resistance gene tet(M), which confers resistance to both minocycline and doxycycline. These results demonstrate the importance of timely utilization of the newly proposed and approved breakpoints.—Hnot ML, Cole LK, Lorch G, Papich MG, Rajala-Schultz PJ, Daniels JB

Demodicosis—What Is New?

Demodex canis, the mite most commonly implicated as the cause of demodicosis, is transferred from bitch to nursing pup shortly after birth. Although the mite typically does not cause disease, in cases of genetic predisposition (breed, short hair coat), poor nutrition, stress, endoparasites, estrous, debilitating diseases, or immunodeficiency, juvenile-onset demodicosis may occur, presenting in either a localized or generalized form. Adult-onset demodicosis may be triggered by drugs or diseases altering the immune response or can be idiopathic. Characterized initially by erythema, papules, scaling, alopecia, and comedones as the mites colonize the hair follicles, severe disease may ensue, causing significant inflammation and pustules, follicular rupture and furunculosis, and deep lesions and crusting. Diagnosis is typically made with deep skin scraping or trichogram; acetate tape preparation with skin squeezing may be more sensitive than deep skin scraping. Biopsy is sometimes necessary. Localized disease is typically self-limiting and resolves spontaneously. In breeding kennels, removal of affected dogs of breeds at risk for juvenile demodicosis can reduce, if not eliminate, juvenile generalized demodicosis. Treatment of underlying bacterial infections is standard. Likewise, underlying diseases must be addressed. Amitraz topical rinse and oral ivermectin and milbemycin oxime are the most commonly used miticidal treatments. Side effects of amitraz are typically reversible with yohimbine. Ivermectin is not recommended in breeds commonly affected by the MDR-1 gene mutation, and any pets undergoing this treatment should be closely monitored for signs of neurologic depression. Treatment should continue for 4 weeks following the second consecutive negative monthly skin scraping.—Mueller RS

Dead Bugs Do Not Mutate

Maximizing the efficacy of chosen antibiotics is crucial to limiting the development of resistant bacterial populations. Bactericidal therapy should be chosen whenever possible, and attention should be paid not only to choosing an appropriate antibiotic but also to administering a dosage sufficient to limit survival of resistant mutants. In vitro studies mainly determine bacteriostatic activity of an antibiotic. This may call into question the clinical relevance of susceptibility testing. Susceptibility testing attempts to determine the minimum inhibitory concentration (MIC) of an antibiotic, defined as the lowest concentration of the antibiotic that will inhibit visible growth of the organism. However, to effectively treat disease in a clinical setting, concentration of the antimicrobial agent at the site of infection should be 1 to 5 times the MIC. Bacterial resistance to antibiotics can either be inherited (intrinsic resistance) or acquired horizontally. Plasmids, bacteriophages, and transposons are all involved in spreading antibiotic resistance in bacteria through horizontal gene transfer. The mutant prevention concentration is considered the drug concentration above which resistance is not usually expected to occur, but testing is more difficult and may not be readily available to the average clinician.—Rankin SC

Salamanders, Skin, & Stem Cells

Urodeles, including salamanders, can regenerate body parts—an ability useful in studies on regenerative medicine. Successful regeneration depends on limited inflammatory response, antimicrobial defenses, mechanisms to avoid scarring, and regeneration in the original pattern. Mechanisms involved in appendage replacement involve plasticity of differentiated cells, positional identity, memory of regenerate, nerve dependence of regeneration, indefinite or strong replication proliferation potential, and species-specific proteins supporting positional identity or de-differentiation in tissues. Some of these traits are present in mammalian skin. Plasticity of cells, or the ability of cells to transform, includes transdifferentiation (changing from 1 cell type to another), differentiation (commitment to a less specialized cell type), or dedifferentiation (cells becoming more primitive). Experimental evidence suggests that adult mammals possess the repressed genetic capacity within cells to express dedifferentiation, but more studies are needed to clarify the gene-expression mechanisms. Studies of stem-progenitor-committed cells within the epidermis (basal cells) also provide information about renewal and differentiation. Scar-free healing in skin seems to relate to the presence of antiinflammatory macrophages to mitigate fibrosis. Research is underway on using treatments such as gene therapy or stem cell treatments to encourage dedifferentiation, promote anti-inflammatory macrophages, and encourage growth promotion. Mesenchymal stem cells (MSCs) have been studied extensively for their immune-modulating effects to reduce inflammation in autoimmune diseases, chronic inflammatory diseases, and fibrosis. The author mentions preliminary data supporting the use of MSCs for perianal fistulas. These studies highlight the potential for exciting advances in regenerative medicine.—Hoffman AM

Antibacterial Effect of Acetylcysteine on Common Canine Otitis Externa Bacterial Isolates

Because of bacterial resistance to current treatments, concern about the development of further resistance, and the narrow variety of FDA-approved medications available, canine otitis externa can be formidable to treat. Even approved treatments may contain ototoxic components. Given these factors, the study authors sought to investigate alternative safe, effective treatment options—in particular acetylcysteine, a nonantibiotic and otoprotective compound. Twenty-two isolates derived from clinically active canine otitis externa cases—including Staphylococcus pseudintermedius, Pseudomonas aeruginosa, Corynebacterium spp, and β-hemolytic Streptococcus spp—were grown on agar and transferred to broth; acetylcysteine was added to broth to concentrations starting at 160 mg/mL and serial microdilution assays were performed for all isolates. Acetylcysteine minimum inhibitory concentration (MIC) was determined for each pathogen. MIC values were 9.7 mg/mL for S pseudintermedius, 10.3 mg/mL for P aeruginosa, 7.9 mg/mL for Corynebacterium spp, and 8.3 mg/mL for β-hemolytic Streptococcus spp. These findings identify antibacterial inhibitory properties of acetylcysteine against various bacterial pathogens, suggesting that it might have utility in the treatment of canine otitis externa.—May ER, Stainbrook KA, Bemis DA

Validation of a Smartphone App (Itchology) for Scoring Owner-Assessed Pruritus Severity in Dogs

An important component of a veterinarian’s dermatological history is a pet owner’s assessment of pruritus. A smartphone application called Itchology was developed to help owners score and graph their pets’ pruritus on a daily basis. The owner uses a vertical slider to choose a numerical value ranging from 0 to 10 in one-tenth increments while scrolling through 6 corresponding behavior descriptions. This study evaluated pruritus severity as scored with Itchology compared with a previously validated canine pruritus severity scale. Fifty dogs presenting to a referral veterinary dermatology practice had their pruritus scored by owners via Itchology and CPSS at the beginning of the consult and again 15 to 20 minutes later. Agreement between the 2 methods was statistically evaluated, and the results suggested that the Itchology application was a valid, reproducible tool for owner-scored pruritus severity.—Plant JD, Neradilek MB, Polissar NL

Biology of the Cat Flea: What’s New in 2015?

Whereas it has been demonstrated that fleas spend most of their time on 1 host, new research indicates that a percentage of fleas will move on and off the host or between hosts before reaching reproductive status, at which point movement off the host is generally limited. This interhost movement raises concerns about the spread of infectious diseases, including Bartonella spp, and management of flea allergy dermatitis. The author notes that recent work has given a means of tracking response to preventative care, as flea reproduction is centered on widespread male availability. Studies have shown that a gender shift in the flea population occurs if flea reproduction is inhibited by insecticidal or insect-growth-regulator treatments given to pets. If home trapping shows a steadily higher male count, it could indicate a positive response to therapy; a lack of gender shift would indicate either treatment failure or presence of untreated flea hosts. With continual exposure of family pets to visiting pets in the home and wildlife habitat in the backyard, scrupulous flea control beyond just the warmer months is recommended. New research will continue to guide flea-control development.—Dryden MW

Vasculitis & Other Ischemic Dermatopathies

Vasculitis is a common dermatopathy pattern indicating inflammation of the blood vessel walls. Cause may be infectious (eg, bacterial, viral, fungal, rickettsial, protozoal), inflammatory, immune-mediated (eg, systemic lupus erythematosus), iatrogenic (vaccine and drug reactions), or idiopathic. Pathogenesis typically involves type III hypersensitivity (antigen/antibody complex deposition), although hypersensitivity types I and II sometimes play a part. Clinical appearance can vary based on cause and the extent and severity of vascular compromise. Signs range from alopecia and wheals to edema, crusting, erosion, ulceration, necrosis, or raised erythematous plaques. Systemic signs (eg, pain, fever, noncutaneous organ involvement) may be present as well. Vaccine-induced vasculitis causes varying degrees of alopecia, crusting, erosion, and ulceration in areas with poor collateral circulation (eg, tail tips, paw pads, pinnae, nasal planum); “punched out” footpad lesions are particularly suggestive. Cutaneous and renal vasculopathy occur in racing greyhounds with multifocal areas of erythematous swelling on the ventral abdomen and extremities that progress to ulcers and pitting edema. A verotoxin produced by Escherichia coli in raw beef is suspected. Diagnosis of vasculitis is based on clinical signs and biopsies obtained from the active edges of lesions. Careful history and diagnostic workup is needed to detect underlying causes. Treatment involves the identification and elimination of underlying disease, anti-inflammatories, pentoxifylline, and in more advanced cases, corticosteroids and immunosuppressive therapy. Focal lesions may respond to topical tacrolimus.—Pucheu-Haston CM)

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