Page 1391 - Small Animal Internal Medicine, 6th Edition

CHAPTER 83 Clinical Pathology in Greyhounds and Other Sighthounds 1363

volume expansion associated with chronic conditioning and that all measured thyroid hormone concentrations were
training; however, this mechanism does not explain why within their respective reference limits. Only 65 sighthounds
VetBooks.ir only some protein fractions are affected or why they persist (16.3%) had additional abnormalities suggestive of hypothy-
roidism (high serum TSH concentration or positive thyro-
after Greyhounds retired from racing. It has been recently
reported that mean serum immunoglobulin A (IgA) and
with standard (non–breed-specific) reference limits, 154 of
IgM concentrations in Greyhounds are lower than in non- globulin autoantibody [TGAA]). In addition, when compared
Greyhounds, which may contribute to the low β-globulin 282 Salukis (54.6%) had tT 4 values, and 67 of 216 Salukis
concentrations in Greyhounds (Clemente et al., 2010). (31%) had fT 4 values below reference limits. These findings
The concentration of acute-phase proteins in Greyhounds support the fact that other sighthound breeds also have low
has been evaluated (Couto et al., 2009). Serum concentra- serum tT 4 concentrations.
tions of C-reactive protein (CRP), haptoglobin (Hp), acid-
soluble glycoprotein (ASG), ceruloplasmin (CP), and serum CARDIAC TROPONINS AND PRO-B
amyloid A (SAA) were measured and compared between a NATRIURETIC PEPTIDE
group of healthy RRGs and age- and gender-matched healthy Previously documented cardiovascular findings in healthy
non-Greyhound controls. The concentrations of Hp, deter- Greyhounds included a higher heart weight–to–body weight
mined by colorimetric and immunoturbidimetric methods, ratio, higher left ventricular free wall thickness, functional
and ASG were significantly lower in Greyhounds than in murmurs with no detectable structural or physiologic abnor-
non-Greyhounds. CRP and CP concentrations were not sig- malities, and higher vertebral heart scores (VHSs) than non-
nificantly different between groups, and SAA concentrations Greyhounds. Cardiac troponin I (cTnI) is a polypeptide
were below the detection limit in all dogs. Because Hp and found specifically in cardiac muscle. Serum concentrations
ASG migrate in the α-globulin fraction, results from this of cTnI have been used as diagnostic and prognostic indica-
study may explain the low α-globulin concentrations in tors of heart disease, including cardiac infarction in humans
Greyhounds. and cardiomyopathy in dogs. Greyhounds have significantly
higher serum cTnI concentrations compared with non-
THYROID HORMONES Greyhounds; however, no significant differences in serum
Greyhounds, Whippets, Salukis, Scottish Deerhounds, cTnI were noted between Greyhounds and Boxers with and
Sloughis, and other sighthound breeds have basal total T 4 without arrhythmogenic right ventricular cardiomyopathy
(tT 4 ) concentrations below non–breed-specific reference (ARVC; LaVecchio et al., 2009). Interestingly, several Grey-
ranges. Free T 4 (fT 4 ) concentrations can also be low, although hounds in our study had cTnI concentrations within or
not to the same extent as tT 4 . However, thyroid-stimulating above the range of Boxers with ARVC. Greyhounds with a
hormone (TSH) concentrations are normal; in Greyhounds, heart murmur, high VHS, and high cTnI level could be
they are in the lower quartile of the RI (Shiel et al., 2007b, incorrectly diagnosed with myocardial disease; thus until a
2010). Highly variable triiodothyronine (T 3 ) concentrations more precise reference range is established, caution should
have been reported; however, fT 3 concentrations in Grey- be used when interpreting serum cTnI concentrations in
hounds are usually below non–breed-specific reference Greyhounds with suspected cardiac disease.
ranges. No increase in the tT 4 concentration after the admin- N-terminal pro-B-type natriuretic peptide (NT-proBNP)
istration of exogenous TSH has also been described in Grey- is a cardiac biomarker whose plasma concentration is high
hounds (Gaughan and Bruyette, 2001). Shiel et al. (2007b) in some dogs with cardiopulmonary disease. NT-proBNP is
investigated thyroid hormone concentration in pretraining a diagnostic tool that can be used to help determine if a
Greyhounds. Young pretraining Greyhounds had lower tT 4 patient has congestive heart failure. Greyhounds have func-
and fT 4 concentrations and a tendency toward higher total tional heart murmurs, relative cardiomegaly, and high serum
T 3 concentrations when compared with non–breed-specific cTnI concentration.
reference ranges. We prospectively evaluated healthy client-owned dogs
A recent study by Shiel et al. (2010) retrospectively including RRGs and non-Greyhounds and found that
assessed the use of serum thyroid hormone concentrations plasmaNT-proBNPconcentration in Greyhounds was sig-
by veterinarians to diagnose hypothyroidism in 398 sight- nificantly higher than in non-Greyhound control dogs (946
hounds, including Greyhounds (n = 347) and other sight- versus 632 pmol/L; P < 0.005); 46% of Greyhounds had NT-
hounds such as Borzois (n = 22), Salukis (n = 11), Irish proBNP > 1000 pmol/L.
Wolfhounds (n = 14), and Scottish Deerhounds (n = 4). A Again, using generic RIs for dogs will result in classifying
cross-sectional study was also performed to assess serum numerous Greyhounds as having heart disease when running
thyroid hormone concentrations in healthy Salukis. Practi- these assays.
tioners who had submitted blood samples for thyroid
hormone testing had diagnosed hypothyroidism in 286 of Renin, Angiotensin, Aldosterone
398 (71.9%) sighthounds on the basis of low serum concen- Given that Greyhounds have unique cardiovascular features,
trations of tT 4 or tT 3 alone. Seventeen sighthounds (4.3%) including the fact that they have well-documented white coat
also had low fT 4 or fT 3 concentrations, and 30 sighthounds hypertension, we evaluated the RAAS in 20 Greyhounds and
(7.5%) were diagnosed with hypothyroidism despite the fact 20 age- and weight-matched non-Greyhound dogs (Martinez