Thank you for responding to our April survey! Here are the results:

Canine hypothyroidism: A not-so-obvious diagnosis

Canine hypothyroidism is one of the most prevalent, but also one of the most commonly overdiagnosed endocrinopathies in dogs. The onset of clinical signs is insidious, occurring over months to years. Left undiagnosed and untreated, hypothyroidism can contribute to morbid obesity, recurrent severe dermatological disease and neuropathy, and predispose the dog to a host of other ailments. Hypothyroidism can often be difficult to diagnose due to suppression of thyroid function by nonthyroidal illness and many medications such as phenobarbital and steroids. Furthermore, some breeds, such as greyhounds, have a T4 level that falls within the low normal range or below the reference interval.

As you can see from the above survey results, the majority of Diagnostic Edge respondents (67%) recognize the complexity in diagnosing hypothyroidism in dogs as they utilize two or more tests to help evaluate thyroid function. In dogs with signs compatible with hypothyroidism, a Total T4 below the reference interval should be corroborated by further diagnostics, and possible nonthyroidal illness should be investigated before thyroid supplementation is instituted. A truly hypothyroid patient will often respond well to therapy, showing great improvement in clinical signs, which naturally leads to pet well-being and client satisfaction.

See the IDEXX SNAP T4 Test article in last month’s issue.

Featured case study:
7-year-old neutered male beagle, Bob
by Dr. Benn Doyle, Westfield Veterinary Group and Wellness Center, Westfield New Jersey

Full history
In addition to muscle tremors and PU/PD, Bob had a history of mild, intermittent interdigital dermatitis and mild obesity. He has otherwise been doing well and is current on all appropriate vaccinations as well as heartworm, flea/tick and intestinal parasite prophylaxis. Recent results from a SNAP® 4Dx® Test were negative as was a routine fecal analysis. He has been on a weight management diet and has lost approximately eight pounds over a
ten-month period; his weight has improved from 60.5 to 52.2 pounds.

Physical examination
On presentation, Bob was bright, alert and in good body condition. He had a slightly pendulous abdomen with palpable cranioventral organomegaly. Ambulation was normal, despite palpable crepitus in both stifles, as were all peripheral reflexes and cranial nerve assessment. There were no proprioception deficits and no obvious muscle tremors during the examination.

Differential diagnoses
The list of differentials included partial idiopathic epilepsy (atypical age of onset), osteoarthritis or other musculoskeletal disease, neuropathy, systemic lupus erythematosus, rheumatoid arthritis, myasthenia gravis, central nervous system diseases such as granulomatous meningoencephalitis (GME) or neoplasia, trauma, infectious etiologies such as toxoplasmosis or neosporosis, insulinoma and/or hypoglycemia, chronic renal failure, hypothyroidism and hyperadrenocorticism.

Diagnostic plan
A complete blood count (CBC), general chemistry profile including electrolytes, complete urinalysis and urine culture were performed in order to assess potential primary and secondary organ involvement.

Laboratory data

Erythron—No significant quantitative or morphological abnormalities were noted.

Leukon—The absolute lymphocyte count is low outside the reference interval; however, this is considered to be insignificant; the potential for a glucocorticoid influence should be considered. No morphologic abnormalities were noted.

Thrombon—No significant quantitative or morphologic abnormalities were noted.

Clinical chemistry

Liver panel—There is a moderate increase in ALKP supportive of either a glucocorticoid influence or cholestasis. The slight lymphopenia in the CBC may be supportive of a significant glucocorticoid influence; however, there are no other significant supportive hematologic changes (neutrophilia, eosinopenia, monocytosis, erythrocytosis, etc.) and there are no other clinical chemistry or urinalysis findings that support cholestasis. Since the increased ALKP does not appear directly related to the presenting clinical signs, re-evaluation and potential investigation into underlying hyperadrenocorticism should be considered.

Acid-base panel—There is a minimal decrease in chloride, which by itself might be considered insignificant; however, when compared to the mid-within-reference-interval sodium, this change is significant. Chloride and sodium will generally follow one another and commonly follow water balance in the animal. The low chloride value compared to the normal sodium value supports either chloride sequestration or loss. There is no further support for loss, since no clinical observation of vomiting was reported and mild loss associated with sequestration should be considered as a cause. Slight simple metabolic alkalosis is supported by the finding of a slightly increased TCO2 or bicarbonate and a normal anion gap suggesting retention of TCO2 to maintain electroneutrality.

Kidney panel—There is no azotemia; however, there is an isosthenuric urine (see below), which is extremely uncommon for a dog with normal hydration. Dogs typically will have a urine specific gravity greater than 1.025. There is a mild hypercalcemia, which does not appear to be associated with renal failure since only potential loss of urinary concentrating ability is observed and there is no evidence of measurable decreased glomerular filtration rate. The degree of hypercalcemia is well within the third standard deviation from the mean for this measured analyte and may merely be a normal finding for this animal; however, there are clinical signs suggestive of an underlying problem and further investigation is warranted. Investigation into possible hypercalcemia of malignancy and primary hyperparathyroidism are warranted if previous total calcium measurements in this animal during health were significantly lower than this current measurement or if repeated analysis reveals a persistent hypercalcemia. A previous total calcium (1.5 years previously) was 11.8 mg/dL; therefore, further investigation is warranted. Other possible causes for a lack of concentrating ability include early renal disease, hyperadrenocorticism, psychogenic polydypsia with medullary washout, pyelonephritis, diabetes insipidus and possible hypercalcemia. The mild proteinuria in the face of a nonconcentrated urine may be of significance and further investigation including determination of the urine protein:creatinine ratio would be warranted. A urine culture was negative.

Diagnostic imaging

Figure 1: Thoracic radiographs – V/D view

Figure 2: Thoracic radiographs - right lateral view

Thoracic radiographs
Three view thoracic radiographs revealed a radiodense area in the right caudal lung lobe on the V/D view that was not visualized on the lateral views. A mild-to-moderate bronchial pattern was evident on all views.

Figure 3: Ultrasound image of left parathyroid nodule

Abdominal and cervical ultrasound
The liver was mildly hyperechoic throughout with moderate, diffuse enlargement and smooth rounding of all lobe margins. There was mild bilateral adrenal enlargement. No other significant abnormalities were noted. The finding of diffuse hepatomegaly combined with bilateral adrenal enlargement is suggestive of pituitary-dependent hyperadrenocorticism. Cervical ultrasonography revealed a small, smooth, hypoechoic mass in the left parathyroid gland.

Further diagnostics

Thyroid panel—The total T4 was on the low end of the reference interval and a Free T4 by equilibrium dialysis was below the reference interval limits suggesting possible hypothyroidism. Contributing nonthyroidal illness should be considered as a reason for the low Free T4 value, although Free T4 is typically less suppressed by nonthyroidal illness compared to total T4 and will generally be decreased with only severe illness.

Parathyroid panel—Based on the history, clinical signs, the presence of hypercalcemia and the discovery of a parathyroid nodule on ultrasound, a parathyroid hormone (PTH) level was evaluated together with an ionized calcium level. The PTH level was slightly elevated supporting a tentative diagnosis of primary hyperparathyroidism light of the mild hypercalcemia; however, the ionized calcium was within reference interval limits. This may be due to improper sample handling, which is essential for accurate measurements; ionized calcium is labile and, therefore, best performed patient-side to obtain reliable results.

Therapeutic plan
Bob was referred for surgical removal of the left external parathyroid gland and associated mass. The histopathologic diagnosis was parathyroid adenoma.

Figure 4: Low magnification of the left external parathyroid gland that was enlarged and well delineated with no evidence of local tissue invasiveness. At high magnification (inset) the neoplasm is composed of closely packed, uniform, mononuclear epithelial cells supported by a delicate fibrovascular stroma.

Final diagnosis
Primary hyperparathyroidism, possible pituitary-dependent hyperadrenocorticism and hypothyroidism.

Clinical case outcome
Recovery from surgery was uneventful. Follow-up calcium levels postoperatively were within the reference interval limits. Further evaluation of possible hypothyroidism and hyperadrenocorticism was recommended one to two months postoperatively. Three months after surgical removal of the parathyroid adenoma, the total T4 level was 4.7
(RI = 1.0–4.7 µg/dL). An ACTH test was then performed and results were supportive of hyperadrenocorticism and additional investigation is planned for further characterization.

References

1. Taboada J. Disorders of Calcium Regulation in the Dog and Cat. Proceedings from NAVC Conference, Vol 22, 477-479.
2. Duncan JR et al. Veterinary Laboratory Medicine: Clinical Pathology, 4^th ed. Iowa State University Press; 2003.
3. Stockham SL et al. Fundamentals of Veterinary Clinical Pathology, 1^st ed. Iowa State University Press; 2002.

The recommendations contained in Diagnostic Edge educational materials are intended to provide general guidance only. As with any diagnosis or treatment, you should use clinical discretion with each patient based on a complete evaluation of the patient, including history, physical presentation and complete laboratory data. With respect to any drug therapy or monitoring program, you should refer to product inserts for a complete description of dosages, indications, interactions and cautions.

Tell us what you think of this case, or let us know if you have a case that you would like to submit. E-mail us at diagnosticedge@idexx.com to get the process started.

IDEXX Learning Center

The IDEXX Learning Center provides knowledge you can put into practice. Take part in the evolution of animal diagnostics through an ongoing educational partnership with leading veterinarians from across the globe and take advantage of a wide range of education resources, reference materials and events. Visit the IDEXX Learning Center to see a full listing of available Webinars, seminars and online training courses from IDEXX.
 

Create your own account on the IDEXX Learning Center and see how IDEXX can help you reach your educational goals!

Here are some of the opportunities available this month:

• A Clinical Approach to Fluid Therapy
  Dr. Stephen DiBartola
• The Complete Urinalysis
  Dr. Rick L. Cowell
• The Management of Common Bleeding Disorders
  Dr. Urs Giger

See a full listing of webinar opportunities >

• Canine Pancreatitis: Diagnosis and Management
• IDEXX VetTest Certificate Course
• Testing for and Managing Retrovirus-Positive Cats

See a full listing of online training opportunities >

• Feline Heartworm Disease in Everyday Terms
  Dr. Lynn Buzhardt
• Lyme Disease for the Canine Practitioner
  Dr. Steven Levy
• Coughing Cats: Asthma or Heartworm Disease?
  Dr. Susan Little
• The Value of Now: How patients, clients and veterinary practices can benefit from in-house diagnostics
  Dr. Jim Irwin

See a full listing for seminar opportunities >

IDEXX Catalyst Dx™ and SNAPshot Dx™ Analyzers!

Watch the video of CEO Jonathan Ayers as he talks about these revolutionary additions to the IDEXX VetLab Suite!

Watch the video and sign up to receive more communications from your peers.

• Get updates on these two revolutionary analyzers
• Hear what other veterinary professionals are saying about them
• Ask questions and tell us what you think!

The two newest additions to the IDEXX VetLab® Suite increase your in-house diagnostic capabilities and allow you to offer your patients and clients an increased level of care:
real-time answers at the point of service in just one visit.

The Catalyst Dx™ and SNAPshot Dx™ Analyzers are integral parts of the IDEXX VetLab® Suite. For more information, visit www.idexx.com/vetlab.

Advance vector-borne disease health care in your practice

Join the IDEXX Vector-Borne Disease Education Program now and get rewards and tools to help you get started or step up your protocols and increase customer compliance!
 (2.17 MB)

Here’s how to get your travel mug, $10 Starbucks Card and four CE credits:*

1. Complete the program form and fax it to IDEXX at 1-207-556-8241.  (2.17 MB)
2. Log on to idexxlearningcenter.com to register and complete these two courses:

3. Receive:*

• a FREE travel mug
• $10 Starbucks Card!
• four CE credits – RACE approved

Enroll your practice today!  (2.17 MB)

For more information on vector-borne disease courses visit idexxlearningcenter.com.

Offer expires June 30, 2008. Offer is limited to the first 1,000 individuals to complete the two courses and fax the completed form to IDEXX. Allow 4–6 weeks for delivery of rewards.

IDEXX Practice Developer® program now includes IDEXX Digital Imaging

On January 1, 2008, we introduced the new program, which features a simplified points calculation and increased opportunities to earn. One new earning opportunity is through IDEXX Digital Imaging. If you have any of our digital imaging systems, you may earn additional Practice Developer points. We count the Extended Maintenance Agreements you maintain on our digital imaging systems toward your Practice Developer purchase volume, and we give you an extra half-percent boost in your overall earning percentage!

IDEXX Practice Developer is a points-based recognition program designed to continually thank you for every purchase, big or small, and to help you save up for diagnostic and management tools that can help grow your practice. We’ve made it as simple as possible for you to make the most of your everyday purchases.

Here’s how it works:

• You earn points on IDEXX purchases: 1 point = 1 dollar
• Save them up to invest in diagnostic tools that can help grow your practice
• Call your IDEXX representative at 1-800-248-2483 to spend points on any IDEXX product or service
• We track the points for you
• No membership fees or paperwork

Try our easy point calculator to see how much you can earn.

Already enrolled?
No need to re-enroll in the enhanced program. You’ll be receiving your new statement soon.

Ready to enroll?
Call 1-800-248-2483 or visit the Practice Developer site for more information.

VetStat® Analyzer Calibration Tip

The VetStat® Electrolyte and Blood Gas Analyzer is the only veterinary-specific in-house blood gas analyzer.

• Provides fast, accurate results for electrolytes, blood gases, acid-base balance, ionized calcium, glucose
• Run samples of whole blood, plasma and serum on single-use disposable cassettes
• Designed for simple and rapid operation by any staff member
   

Wipe cassettes before use
Packaged at 100% relative humidity, the
VetStat cassette is wet when you remove it from its pouch. You must wipe the cassette with a lint-free wipe such as a Kimwipe before placing it in the VetStat analyzer. Otherwise, the liquid from the cassette will evaporate as the cassette is warmed to 37°C during the calibration process. The evaporation affects the optical path and the analyzer cannot establish a uniform calibration. When this occurs, the analyzer will reject the cassette. Errors can occur as a result of not properly wiping the cassette before use.
 

For more information on the VetStat analyzer, visit www.idexx.com/vetstat or call 1-800-355-2896.

With FREE continuing education credit!*

NOW Approved in the United States, Australia and parts of Canada!†

Have you taken advantage of every qualifying Interactive Challenge for FREE continuing education (CE) credits?

Every Interactive Challenge from June 2006 on has each been worth 0.5 continuing education credit in the United States—and you get the credit just for participating! Check out the Diagnostic Edge archive and take any qualifying challenges you may have missed. Don’t let these fun credits slip away!

Question:

1. Which of the following is the BEST interpretation for this specimen?

1. Inflammation – hypersensitivity response
2. Inflammation – pyogranulomatous inflammation
3. Neoplasia – sarcoma with secondary inflammation
4. Neoplasia – mast cell tumor with secondary fibroplasia
5. Neoplasia – mixed sarcoma and mast cell tumor

Figure 1:	Aspirate of a firm, well-defined skin mass on the distal forelimb of a dog, Wright’s stain, 100x objective field of view.

Not a Diagnostic Edge subscriber? Subscribe now!

All fields are required for continuing education credit records.

Thanks for taking the Diagnostic Edge Interactive Challenge!

*Each interactive challenge meets the requirements for 0.5 hour of continuing education credit in jurisdictions that recognize AAVSB’s RACE approval, however, participants should be aware that some boards have limitations on the number of hours accepted in certain categories and/or restrictions on certain methods of delivery of continuing education.

AAVSB Provider Number 106

^†Interactive challenges are also approved in Australia for 0.5 AVA Vet Ed Point and from the following Canadian Veterinary Medical Associations: Alberta, Saskatchewan, New Brunswick and Prince Edward Island.

All ®/TM marks are owned by IDEXX Laboratories, Inc. or its affiliates in the United States and/or other countries.