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Preview: New York Vet 2017

Dermatology

|October 2017

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New & Old Tricks for Dermatologic Procedures

Accurate skin disease diagnosis relies on a systematic approach, which includes obtaining signalment and history, performing a complete dermatologic examination, and performing appropriate tests as indicated.

Determining degree of pruritus, types of lesions present, and pattern or distribution of lesions can help shorten the list of differential diagnoses. Primary lesions (eg, papules, vesicles, plaques, cysts) develop directly from disease processes. Secondary lesions (eg, lichenification, hyper- or hypopigmentation, scales, alopecia) develop from primary lesions and are often induced by the patient or the environment. In-house diagnostics often prove helpful for confirming diagnosis and monitoring patient response to therapy.

Skin scrapings are most often used in diagnosing parasitic infestations. Tape preparations are useful for detecting superficial parasites and organisms on dry, scaly skin. Impression smears allow for detection of organisms and help determine presence or absence of various cells; they are particularly useful for moist, greasy, or exudative lesions. Exudate preparations are used when direct impression smears are not possible (eg, for external ear canal, deep skin folds). 

During cytologic examination, cell types, inflammatory response, presence or absence of organisms, and characterization and numbers of organisms present should be noted and recorded. Skin biopsies with histopathology should be conducted in patients that have persistent lesions, suspected neoplasia, undiagnosed alopecia, or vesicular or unusual dermatoses.

Bacterial culture is indicated when empiric antibiotic therapy fails to resolve infection; positive results should be interpreted carefully, as nonpathogenic contaminants may be present. Fungal cultures are also useful to diagnose dermatophytosis in patients with or without distinct lesions.—Werner A

FAST in Emergent Patients

Timely assessment of emergent and critically ill patients is necessary to avoid treatment delays, which can increase morbidity and mortality. Focused assessment with sonography for trauma (FAST) has been used as a first-line screening technique for emergencies and as a bedside monitoring tool.

Abdominal FAST consists of 4 standard views—subxiphoid, left flank, midline bladder, and right flank—with the patient in (ideally, right) lateral recumbency. The probe is moved a few inches in several directions and fanned at 45-degree angles until target organs are visualized; approximately 3 to 6 minutes are required to complete all 4 views.

The subxiphoid view aids in assessment of the hepatodiaphragmatic interface, gallbladder, pericardial sac, and pleural space. The left flank view aids in evaluation of the splenorenal interface and areas between the spleen and body wall. The midline bladder view aids in assessment of the bladder apex, and the right flank view aids in examination of the hepatorenal interface and areas between intestinal loops.

Thoracic FAST is performed with patients in left or right lateral recumbency; patients with respiratory distress should be placed in sternal recumbency. The right and left chest tube sites, the right and left pericardial sites, and the abdominal FAST subxiphoid views are evaluated for identification of fluid in the pleural or pericardial space or free air in the pleural space. For the chest tube sites, the probe is held stationary to evaluate for appropriate glide signs, which represent normal lung motion with no chest wall pathology.—Odunayo A

Managing Pruritus: Steroids & Beyond

To successfully treat pruritus, it is important to address underlying causes and secondary factors. Flea bite dermatitis and flea bite hypersensitivity are the most common pruritic skin diseases affecting dogs and cats. Additional parasitic causes include Sarcoptes spp, Cheyletiella spp, and Demodex spp infection. 

Staphylococcus spp, Malassezia pachydermatis, and dermatophyte infections must be controlled. Allergen-specific immunotherapy is the only therapy that can modify or reverse the pathogenesis of atopic dermatitis. Recombinant technology is a recent development in allergen-specific immunotherapy, as are novel routes of administration (eg, sublingual, intralymphatic). Variable response has been seen with antihistamine treatment. 

Corticosteroids have down-regulatory effects in the inflammatory cascade; adverse effects are possible. Corticosteroids are most effective in managing acute flare-ups to break the itch-scratch cycle. Dosages should be tapered.

Cyclosporine is steroid sparing and can be as effective as steroids against pruritus. However, the onset of cyclosporine is slow, and GI side effects are common. Oclacitinib inhibits the IL-31 cytokine function and has additional immunomodulatory effects. Its rapid onset makes it useful for pruritus flare-ups. Adverse effects with chronic use include demodicosis, pneumonia, and other immunosuppressive effects.

Caninized anti-cIL31 monoclonal antibodies have rapid onset, are effective for 4 to 6 weeks, and have no known side effects or drug interactions. Long-term safety and efficacy data are lacking.—Werner A

Diagnosing, Monitoring, & Managing Chronic Kidney Disease

Chronic kidney disease (CKD) has an overall prevalence of 25% to 50% in older dogs and cats. Management focuses on slowing disease progression through early detection, staging, and therapeutic intervention. Although CKD is progressive and irreversible, early detection as well as avoidance of insults (eg, NSAIDs, hypotension, hypertension) can slow progress. 

Early signs include loss of urine-concentrating ability and muscle loss. Azotemia may be an insensitive CKD marker. Blood symmetric dimethylarginine is considered a more sensitive marker and can be used in conjunction with serum creatinine to assess CKD severity; however, it should not be used to monitor trends. 

CKD management should take into account owner goals and home care abilities. Therapeutic interventions focus on improving body and muscle condition, minimizing proteinuria and hypertension, reducing renal secondary hyperparathyroidism, stimulating RBC mass, and maintaining hydration.

Moderate protein restriction may be achieved with therapeutic renal diets, which also restrict dietary phosphorus and sodium and provide omega-3 fatty acids, B vitamins, and antioxidants. Antiemetics, appetite stimulants, and feeding tubes should be used to maintain weight in patients that are unable to maintain caloric needs. 

Proteinuria and hypertension should be controlled with amlodipine and ACE inhibitors as well as angiotensin-receptor blockers. Hyperphosphatemia can be controlled by ensuring adequate hydration, feeding a therapeutic renal diet, and administering a phosphorus binding agent. Darbepoetin along with parenteral iron can be effective for treating anemia.—Tolbert K

What Does Low T4 Really Mean?

Clinical signs of hypothyroidism, a relatively common canine endocrinopathy, can be vague. Common signs include dermatologic disease, lethargy, obesity, and weakness. Other signs (eg, neurologic abnormalities, bradycardia, female infertility) are seen less frequently. Hypothyroidism usually affects neutered middle-aged dogs of either sex. Predisposed breeds include boxers, cocker spaniels, and golden retrievers. Breeds with naturally low total thyroxine (tT4) levels include giant schnauzers, sighthounds, and Irish wolfhounds.

Because breed, illness, drugs, and circulating autoantibodies can affect tT4 concentration, treatment based on this single measurement—especially in the absence of clinical signs—is not recommended. Drugs that can interfere with testing include carprofen, steroids, phenobarbital, and clomipramine. 

Free T4 (fT4) is considered the best diagnostic test for hypothyroidism but can be affected by some of the same factors as can tT4. Equilibrium dialysis for fT4 measurement eliminates false increases caused by autoantibodies and systemic illness. 

Thyroid-stimulating hormone (TSH) levels can be normal in up to 25% of hypothyroid dogs but are usually unaffected by breed, illness, or drugs (except for antithyroid treatments and sulfonamide drugs). Autoantibodies suggest autoimmune thyroiditis, which may be a marker for future hypothyroidism but does not define current thyroid status. A combination of tests is recommended: tT4, fT4, and TSH for best sensitivity and fT4 and TSH for best specificity. 

Cessation of levothyroxine for one week should allow normalization of tT4, fT4, and TSH concentrations. No feline-specific TSH assay is available, but the canine assay can be used with repeat fT4 or tT4 testing. Most cases of feline hypothyroidism are iatrogenic.—Tolbert K 

For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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