Page 138 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 10 · Surgery of the thyroid and parathyroid glands

necessitating an emergency tracheostomy. 2007). The most important clinical sign is consistent
Tracheostomy in the cat requires intensive hyper calcaemia, causing polydipsia and polyuria. Hyper-
VetBooks.ir Chapters 2 and 8). Laryngeal function usually recovers common than that from other causes, and a full investiga-
management and has a high complication rate (see
calcaemia due to primary hyperparathyroidism is less
tion to rule out other causes should always be completed
over a period of 5–7 days postoperatively.
• Recurrence of hyperthyroidism: Intracapsular
Parathyroid adenomas are far more common than
techniques have a higher incidence of recurrence of (Figure 10.7).
hyperthyroidism, subsequent to regeneration of the carcinomas and are usually functional. Rarely, carcinoma
thyroid adenoma from fragments left behind on the may be diagnosed on the basis of histopathological
capsule. Clinical signs tend to be similar to the initial cri teria, but these tumours usually behave in a benign
presentation, and diagnosis is confirmed in the same manner and are non-metastatic. Adenomas usually affect
manner. Some cats may develop adenomas in ectopic a single para thyroid gland (Figure 10.8), but in predis-
thyroid tissue. Scintigraphy may be required to detect posed breeds bilateral adenomas may be present or an
the site of the ectopic thyroid tissue. Radioactive iodine adenoma may develop de novo in the contralateral gland
therapy is the preferred treatment for intrathoracic at a later date.
ectopic thyroid tissue.

Parathyroid disorders

Diagnostics

Diagnosis of primary parathyroid disease relies largely
on the measurement of serum PTH levels, although a
thorough examination of the animal is necessary to rule
out other causes of hypercalcaemia (Figure 10.7). Currently
there is no feline-specific PTH assay, which creates addi-
tional challenges to confirming the diagnosis in cats.
Rarely, parathyroid tumours may be part of a syndrome
involving multiple endocrine neoplasms such as thyroid
carcinoma, phaeochromocytoma and thymoma. Although ight parathyroid adenoma in the dog sho n in Figure 1 . .
scintigraphy has been described for the identification 10.8 The adenoma is visible as a pale nodule on the cranial pole of
of enlarged parathyroid glands, it is not very sensitive or the thyroid gland.
specific, and is not recommended as a means of identify- (© Davina Anderson)
ing parathyroid disease in animals with hypercalcaemia.
High-resolution ultrasonography is much more useful; Clinical signs
guidelines for dogs indicate that parathyroid glands >4 mm Elevation of the serum ionized calcium occurs gradually
across should rouse suspicion of neoplastic disease, and often clinical signs are subtle. Clinical signs may
whereas enlarged glands <4 mm are more likely to be include: lethargy; inappetence; weakness; polydipsia;
hyperplastic (due to other diseases). Parathyroid glands polyuria; hypercalcaemia (with associated renal damage);
are symmetrically enlarged in animals with chronic, pathological fractures; vomiting; constipation; and urolith-
although not acute, renal failure. iasis (calcium phosphate or oxalate). Dogs with hyper-
calcaemia due to primary hyperparathyroidism will have a
Hyperparathyroidism decreased phosphorus level, resulting in a normal calcium
x phosphorus product. This means that the risk of renal
Parathyroid tumours are uncommon in dogs and rare mineralization and renal failure is low. In one study, 95% of
in cats. Dogs usually present at older than 6 years, and dogs with primary hyperparathyroidism had blood urea
a breed predisposition in the Keeshond with autosomal nitrogen and serum creatinine within or below the normal
dominant inheritance has been reported (Goldstein et al., range (Feldman et al., 2005).
Diagnosis Recommended investigations
Hypercalcaemia of malignancy (lymphosarcoma, apocrine gland Complete physical examination for evidence of neoplasia, including diagnostic
carcinomas of the anal sac, multiple myeloma, other carcinomas) imaging of the chest and abdomen. Aspirate lymph nodes and masses
ranulomatous or severe inflammatory disease including ther blood analysis findings and clinical history may be suggestive
pancreatitis and inflammatory bo el disease
Primary hyperparathyroidism Confirm ith parathyroid hormone T assay
Secondary nutritional hyperparathyroidism Clinical history, age
Secondary renal hyperparathyroidism Blood and urine analysis confirm renal failure. adiography confirms
decalcification of bones
Destructive disease of bone (e.g. systemic mycosis) Radiography
Vitamin D intoxication Clinical history (e.g. on therapy for hypoparathyroidism, consumption of rat bait)
Hypoadrenocorticism Blood analysis age history bradycardia associated ith hyperkalaemia
Hypoalbuminaemia Blood analysis, clinical history

10.7 ifferential diagnosis for serum hypercalcaemia.

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