Personal/Professional Development

Collection of Commentaries on Veterinary, Medical, and Related Literature

Issue: March/April 2012

Today’s Veterinary Practice is pleased to provide a brief overview of sessions presented by members of our editorial team—editorial board members and authors—during the NAVC Conference 2012 in Orlando, Florida. You can purchase proceedings at navc.com/conference/program/proceedings.

PARASITOLOGY

Truths, Half-Truths, & Myths: Understanding Canine Heartworm Disease and Your Role in Heartworm Prevention
Byron Blagburn, MS, PhD; Karen Felsted, CPA, MS, DVM, CVPM; Susan Little, DVM, PhD
NAVC Conference 2012: Small Animal & Exotics Proceedings, p 279

In the next issue of Today’s Veterinary Practice, Dr. Clarke Atkins will be tackling similar questions to the ones below in his article on canine heartworms for our Fact or Fiction column. The following is a sampling of the questions addressed in this session.

Are heartworm preventives 100% effective at protecting dogs from heartworm infection? In the past, to receive FDA approval, heartworm preventives were required to be supported by studies documenting 100% efficacy in preventing heartworm infection. However, in recent years, some veterinarians have expressed concerns about the potential failure of preventives to consistently protect dogs from infection.
Are heartworms becoming resistant to heartworm preventives? Several studies have been performed to evaluate the efficacy of heartworm preventives. While some of the preventives did not meet 100% effectiveness, they all exceeded 90%, the most commonly accepted threshold for evidence of anthelmintic resistance, therefore, retaining a high level of activity even when faced with a more challenging strain.
Are all canine heartworm tests the same? No: Several factors differentiate heartworm tests from each other. To start, there are two types of tests—enzyme-linked immunosorbent assay (ELISA) technology and immunochromatography/lateral flow methods. In addition, variables, such as paying attention to details when processing samples, method of storage, and shelf life can affect the test results. Regarding ease of use, the following features should be considered: time needed to perform test, ease of determining results, cost, and whether other organisms are detected.
Why is it important that all dogs be tested annually for heartworm? Lack of client compliance coupled with the potential for resistance makes regular testing a must, and both the American Heartworm Society and The Companion Animal Parasite Council recommend annual testing.
How do we communicate more effectively with clients?
- Prevention Protocols: Set clear standards for the practice team regarding heartworm testing and prevention.
- Training: Everyone in the practice must be on the same page regarding testing and prevention standards.
- Communicate: Provide clients with consistent and specific recommendations regarding parasite prevention.
- Educational Materials: Communicate with clients in several ways—handouts, practice website, enewsletters/email, just to name a few ideas.

SMALL MAMMAL MEDICINE

The Anemic Ferret: Where to Go When the Answer Isn’t Obvious
Angela M. Lennox, DVM, Diplomate ABVP (Avian)
NAVC Conference 2012: Small Animal & Exotics Proceedings, p 1468

Mucous membranes of a profoundly anemic ferret; ferrets tolerate chronic anemia well, and occasionally present with PCV as low as 7% to 10%.

Anemia is a common sign of disease in pet ferrets; multiple etiologies necessitate a thorough diagnostic approach. The following conditions can produce anemia in other species and are documented in pet ferrets: trauma, surgery, chronic renal failure, ectoparasitism, Helicobacter-related gastric ulceration, viral disease, hypothyroidism, chronic inflammation, and neoplasia, especially leukemia. The most thoroughly described disease in the ferret is pancytopenia, which results from chronic estrogen toxicity; however, it is uncommon in the U.S. due to the paucity of intact female ferrets.

Of interest is a published case of apparent immune-mediated pure red-cell aplasia in an 8-month-old ferret that responded to treatment with prednisone, cyclosporine, and azathioprine. Other practitioners, including the author, have noted similar cases described cytologically as red-cell hypoplasia or maturation arrest. All occurred in younger ferrets and not all responded to therapy.

Diagnosis of anemia is straight forward; however, pinpointing the etiology is more challenging and may necessitate bone marrow aspiration and core biopsy. The approach is similar to that in the domestic cat. Treatment includes supportive care, including blood transfusions when indicated, and treatment of the underlying disease condition.

DERMATOLOGY

Dermatology Tests for Everyday Practice
Paul B. Bloom, DVM, Diplomate ACVD & ABVP (Canine & Feline Practice)
NAVC Conference 2012: Small Animal & Exotics Proceedings, p 667

Dermatologic diagnostic testing should be performed in all small animal hospitals. Tests can be separated into immediate and delayed tests. Immediate tests include:

skin scrapings
impressions smear
ear cytology (if ear disease is present)
fine tooth combing
hair plucks/trichograms.

Delayed tests include:

skin biopsies
Wood’s lamp and fungal culture
bacterial culture and susceptibility
CBC, serum chemistry profile, and urinalysis
adrenal function tests
thyroid profile
dietary elimination food trial
intradermal testing/serum testing and allergen-specific immunotherapy.

Many dermatologic diseases clinically appear the same and only with thorough testing can they be differentiated. For pruritic animals, all immediate tests should be performed. The results of the immediate tests will help determine which delayed tests should be performed.

Critical Points

Dermatologic diagnostic testing should be the standard of care for all dermatologic cases.
Tests can be separated into immediate and delayed tests; for best results, pruritic animals should have all immediate tests performed.
Veterinary technicians should be trained to perform immediate tests and most of the delayed tests.

DENTAL IMAGING

Navigating the Maze of Digital Dental Radiography
R. Michael Peak, DVM, Diplomate AVDC
NAVC Conference 2012: Small Animal & Exotics Proceedings, p 612

Digital radiography is revolutionizing veterinary radiography and, more specifically, dental radiography. There are basically two types of digital dental radiographs: direct and indirect.

Direct digital dental radiography (DDR) captures images by a sensor connected directly via a cable to a computer and displays the image within 10 seconds. These sensors convert the radiation detected into a light charge that results in a gray-scale image on the screen. The direct method sensors are available in sizes 0, 1, and 2.
Indirect digital dental radiography (computed radiography or CR) captures and holds radiation energy through a sensor, typically on a phosphor plate; then this sensor is placed in a laser scanner that reads the varying levels of energy and translates it into shades of gray. The main advantage of the indirect method over the direct method is the larger size 4 (plus sizes 0, 1, and 2).

Some of the most important characteristics to consider when purchasing a digital sensor are:

Resolution: Sensors with resolution greater than 20 lines per mm should have very good resolution.
Ease of software use: Take into consideration everything you need the software to do and then determine what system fits your needs; also inquire about back-up systems as well as storage for images.
Technical support: Make sure that you’ll have assistance with setting up software, and support if problems or damage take place.

ONCOLOGY

What’s New and on the Horizon for Canine Osteosarcoma
Laura D. Garrett, DVM, Diplomate ACVIM (Oncology)
NAVC Conference 2012: Small Animal & Exotics Proceedings, p 1501

(Left image) Anterior-posterior radiograph of radius of doberman with osteosarcoma; treatment with radiation and bisphosphonate zoledronate was instituted. (Right image) Anterior-posterior radiograph of same patient 5 months later; note the remodeling of the bone. The patient had full use of the leg with no need for pain medications.

Despite multiple variations in protocols, the median survival for dogs with osteosarcoma that are treated with amputation and chemotherapy remains at ~ 10 to 12 months. With regard to heritability, a recent study found a mutation in a proto-oncogene (MET) in 70% of rottweilers and < 5% of all other breeds. Diagnostically, fine-needle aspirates and cytology of the bone lesion are diagnostic for the majority of cases; once the cells are identified as sarcoma, alkaline phosphatase staining is a highly sensitive and specific way to confirm bone origin and osteosarcoma.

Prognostically, an elevated serum alkaline phosphatase predicts shorter survival times by 50%. Also, higher numbers of blood monocytes and/or lymphocytes prior to amputation and chemotherapy carried a worse prognosis.

The treatment option associated with longest survival times is amputation, followed by 4 to 6 doses of platinum-based chemotherapy (cisplatin or carboplatin). Doxorubicin may be used, but it is slightly less effective.
For tumors at the distal radius, limb-salvage procedures may save the leg by replacing the tumor-affected section of bone with an implant.
Stereotactic radiotherapy (1–3 very high, targeted doses of radiation) may also treat the local tumor and spare the leg; when combined with carboplatin chemotherapy, survival times were similar to dogs treated with amputation and chemotherapy. Sites other than the distal radius may be treated with this modality.
For palliation, standard radiation therapy can provide increased comfort in the majority of dogs for ~ 4 months. An ongoing study looking at standard radiation combined with bisphosphonate zoledronate (and no chemotherapy) is showing excellent local palliation for a prolonged duration, as well as delayed metastasis; the median survival to date was 368 days.
For dogs with bulky metastatic disease, which historically shows no response to maximum–tolerated-dose chemotherapy, anti-angiogenic therapy with a tyrosine kinase inhibitor, such as toceranib phosphate and/or metronomic chemotherapy (small frequent doses of drugs, such as cyclophosphamide and piroxicam), may be of benefit.

ENDOCRINOLOGY

The Problem Diabetic: A Case-Based Approach
J. Catharine Scott-Moncrieff, MA, Vet MB, MS, Diplomate ACVIM & ECVIM
NAVC Conference 2012, Masterclass

12-year-old spayed female toy poodle with insulin-resistant diabetes mellitus due to hyperadrenocorticism

Indicators of poor diabetic regulation in dogs and cats include: 1) recurrence or persistence of clinical signs of diabetes mellitus, 2) hypoglycemia, 3) inappropriately high insulin dose, and 4) recurrent ketoacidosis.

Persistent blood glucose increases during a blood glucose curve or increased fructosamine concentration may also indicate poor glycemic control, but patient stress and day to day variability should be taken into account when interpreting results.

The most common tools used to determine the cause of poor glycemic control include: 1) complete history and physical examination including body weight, 2) blood glucose curves performed either at home or in the clinic, and 3) measurement of fructosamine concentration.

Laboratory results should always be interpreted in the context of clinical signs and physical examination findings. Common causes of poor glycemic control include: 1) problems with insulin administration, 2) insulin-induced hypoglycemia, which may be occult, 3) short duration of insulin action, 4) use of inappropriate insulin dose or formulation (eg, compounded insulin), and 5) insulin resistance.

Concurrent diseases, such as pancreatitis, hyperadrenocorticism, renal failure, bacterial infection, neoplasia, and heart disease, cause insulin resistance in both dogs and cats. Diestrus or pregnancy in dogs, acromegaly in cats, and some drugs, such as glucocorticoids and progestagens, may also cause insulin resistance. After a thorough history, physical examination, and review of a minimum database (CBC, serum chemistry profile, urinalysis, urine culture), the following diagnostics may be indicated in cats depending on initial clinical findings when insulin resistance is suspected: 1) diagnostic imaging (thoracic radiographs, abdominal ultrasound), 2) serum assays for pancreatitis, 3) thyroid or cortisol testing, and 4) evaluation for acromegaly (IGF-1/growth hormone).

UROLOGY/NEPHROLOGY

Staging Feline Chronic Kidney Disease
Gregory F. Grauer, DVM, MS, Diplomate ACVIM
NAVC Conference 2012, Breakfast Session

Table 1 was developed by the International Renal Interest Society (IRIS) as a guide to stage cats with stable chronic kidney disease (CKD) based on serum creatinine concentration. Serum creatinine concentrations must always be interpreted in light of the cat’s urine specific gravity and physical examination findings (eg, hydration status) in order to rule out pre- and postrenal causes of azotemia. The IRIS stages are further classified by the presence or absence of renal proteinuria (Table 2) and systemic hypertension (Table 3).

Further exploration of renal disease (beyond minimum database) may include urine culture, kidney imaging, and kidney biopsy. Stability of renal function should be assessed by serial monitoring of abnormalities identified during initial characterization of the renal disease; this includes serum biochemistry profiles, urinalyses, quantitation of proteinuria, blood pressure measurement, and follow-up urine cultures and ultrasonography.

Characterization and stabilization of renal disease is most important in earlier stages of CKD when appropriate treatment has the greatest potential to improve or stabilize renal function. Characterization of patient problems becomes more important in later stages of CKD when clinical signs tend to be more severe. In later stages, diagnostic and therapeutic efforts should address issues such as anorexia, vomiting, acidosis, potassium depletion, hypertension, and anemia.

PHARMACOLOGY

Midazolam & Diazepam—What’s the Difference?
Lysa Pam Posner, DVM, Diplomate ACVA
NAVC Conference 2012, Clinical Brief

Benzodiazepines are routinely used in veterinary practice for sedation, muscle relaxation, and behavior modification and also as anticonvulsants and adjuncts to anesthesia (with induction agents or as constant rate infusions). These drugs work by facilitating the action of gamma-aminobutyric acid (GABA), the principal inhibitory neurotransmitter in the central nervous system.