Page 139 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

Diagnosis prognosis should be excellent for complete resolution of
the disease after surgery.
A full blood analysis and urinalysis, as well as radiography The parathyroidectomy procedure is described in
VetBooks.ir ination of the abdomen and neck, should be performed. Oper ative Technique 10.3.
of the abdomen and thorax and ultrasonographic exam-
Ultrasound examination is useful to identify the location of
the tumour and to rule out the 10% of cases that have
masses in more than one gland. Occasionally, advanced Postoperative complications
Hypocalcaemia: Over 50% of dogs will develop some
imaging is indicated when the parathyroid glands appear to degree of hypocalcaemia postoperatively, and there is no
be normal and an ectopic parathyroid tumour is suspected. way to accurately predict those dogs at increased risk.
It is essential to rule out other causes of hyper calcaemia, Intravenous soluble calcium is given to treat acute hypo-
such as granulomatous disease, vitamin D toxicosis, anal calcaemia and oral vitamin D analogues and oral calcium
sac carcinoma and lymphosarcoma, and to investigate for supplementation are given until the animal is able to main-
other concurrent diseases. Hypercalcaemia should be tain normal calcium homeostasis; 1,25-dihydroxyvitamin D
confirmed by measuring serum ionized calcium, and diag- (calcitriol) has the most rapid onset of action and a short
nosis of primary hyperparathyroidism is confirmed by half-life (see Figure 10.6). This helps with dose adjustments
documentation of an inappropriately normal or high serum and prevention of vitamin D toxicosis and hypercalcaemia.
PTH in the face of a concurrent hypercalcaemia.
Ionized calcium should be measured daily and the dose
adjusted to maintain the calcium just below the normal
PRACTICAL TIPS range, allowing stimulation of the normal parathyroid
tissue to regain control of homeostasis. In some cases,
• Lymphoma may be very difficult to rule out in some hypocalcaemia is very resistant to treatment, and medica-
dogs. Where diagnosis is equivocal, referral to a tion and blood tests may be required for some weeks.
specialist centre would be advisable
• Be sure to distinguish between hypercalcaemic Laryngeal paralysis: Rough retraction of tissues during
renal failure and primary hyperparathyroidism examination and surgery of the parathyroid glands or
excessive use of monopolar diathermy may cause bruising
or damage to the recurrent laryngeal nerve. In cases where
Treatment the damage is not reversible over 2–4 weeks postoper-
atively, arytenoid lateralization may be necessary (see
Progression of clinical signs associated with primary hyper- Chapter 7).
parathyroidism is slow and the hypercalcaemia in these
patients is no longer thought to be associated with renal Recurrence of hyperparathyroidism: The blood calcium
failure. However, the treatment of choice remains surgical level should immediately respond to surgery, becoming
removal of the adenoma (Figure 10.9). Preoperative diuresis normal or low. Where there is no response, there may be
with intravenous 0.9% saline may help reduce serum multiple parathyroid tumours, the wrong parathyroid gland
ionized calcium levels to decrease the risk of cardiac may have been removed or the diagnosis was incorrect. In
dysrhythmias and reduce negative feedback on the normal a small number of cases, the surgeon may find no abnor-
parathyroid gland. However, preoperative ionized calcium mal parathyroid tissue at surgery, and the disease is due to
levels and serum PTH levels have not been shown to be an ectopic parathyroid tumour. In this situation, referral for
predictive of postoperative hypocalcaemia (Arbaugh et al., advanced imaging and further investigations would be
2012). After successful parathyroidectomy, ionized calcium appropriate. Predisposed breeds may present months to
should drop to within the normal range within 24 hours. If years later with a second tumour.
the normal parathyroid tissue does not resume homeo-
static function, clinical signs of hypocalcaemia may Hypoparathyroidism
develop 24–48 hours after surgery. This effect can be
attenuated if the animal is prepared preoperatively by Hypoparathyroidism is most commonly associated with
administering vitamin D analogues; given that it usually parathyroidectomy or devascularization of the parathyroid
takes a few days for the vitamin D to affect serum calcium glands during thyroidectomy. It rarely occurs as a primary
levels, this should be started the day before surgery. The disorder; see above under postoperative complications of
thyroidectomy.

References and further reading

Arbaugh M, Smeak D and Monnet E (2012) Evaluation of preoperative serum
concentrations of ionized calcium and parathyroid hormone as predictors of
hypocalcaemia following parathyroidectomy in dogs with primary
hyperparathyroidism: 17 cases (2001–2009). Journal of the American Veterinary
Medical Association 241, 233–236
Brearley MJ, Hayes AM and Murphy S (1999) Hypofractionated radiation therapy
for invasive thyroid carcinoma in dogs: a retrospective analysis of survival.
Journal of Small Animal Practice 40, 206–210
Campos M, Ducatelle R, Rutteman et al. (2014) Clinical, pathologic and
immunohistochemical prognostic factors in dogs with thyroid carcinoma.
Journal of Veterinary Internal Medicine 28, 1805–1813
Caney SMA (2013) An online survey to determine owner experiences and
opinions of the management of their hyperthyroid cats using anti-thyroid
medication. Journal of Feline Medicine and Surgery 15, 494–502
Carver JR, Kapatkin A and Patnaik AK (1995) A comparison of medullary thyroid
emoval of the adenoma sho n in Figure 1 . . carcinoma and thyroid adenocarcinoma in dogs: a retrospective study of 38
10.9
(© Davina Anderson) cases. Veterinary Surgery 24, 315–319

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