Page 1951 - Cote clinical veterinary advisor dogs and cats 4th

976 Thyroid Neoplasia

○ Use passive aspiration. Do not attach • Surgery plus chemotherapy • No clear benefit for chemotherapy after
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syringe, or if a syringe is used to maneu- • RT: external beam or I 131 surgery but should be considered; dogs with
VetBooks.ir • Cytology of regional lymph nodes (superficial requires large doses and is limited to < 10 • Radioiodine therapy: MST of 1 year with
ver the needle, do not actively aspirate.
tumoral vascular invasion or other negative
○ Treatment of malignant tumors with I
prognostic factors might benefit.
Redirect needle only.
facilities in North America.
cervical and mandibular): possible metastasis
unacceptable myelosuppression.
• Three-view thoracic radiographs: possible ○ Dose should not exceed 5 mCi/kg to avoid metastasis present, > 2 years without
metastasis
metastasis ○ Radioiodine spares normal tissues com- • External beam RT: 80% survival at 1 year;
• Ultrasound pared to external beam radiation. MST 2 years.
○ Evaluate carotid artery and jugular vein • Chemotherapy ○ Dogs can survive a long time (MST ≈2
for invasion. ○ ≈50% response seen to doxorubicin, years) even with pulmonary metastasis if
○ Use to guide a needle for aspiration or cisplatin, mitoxantrone, actinomycin D, primary tumor is addressed with RT.
biopsy to avoid vascular structures. and metronomic chlorambucil. ○ After RT, takes at least 8 months to achieve
○ 80% of dogs responded to toceranib full effect.
Advanced or Confirmatory Testing phosphate in an early study (25% had • Negative prognostic factors with regard to
• CT or MRI: do NOT perform a contrast- tumor size reduction; remainder had stable local invasion and resectability or metastatic
enhanced CT until radioiodine has been disease). behavior, or both, include increased size,
determined to not be a treatment option • Thyroid hormone supplementation is location (ectopic or bilateral), attachment
(see below). typically provided after RT or bilateral to underlying structures, high Ki-67 activ-
• Scintigraphy thyroidectomy (p. 525). Keep serum T 4 ity, and vascular invasion (macroscopic and
○ 99m Tc-pertechnetate commonly available concentration in high-normal range to microscopic).
and less expensive, with better resolution suppress TSH.
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compared with I PEARLS & CONSIDERATIONS
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○ 123 I or tracer dose of I can distinguish Nutrition/Diet
thyroid from salivary gland; pertechnetate • Restricted-iodine diets may be recommended Comments
cannot. before radioiodine to cause increased iodine • First, decide whether radioiodine will be
• Immunohistochemistry of biopsy to dif- uptake. considered for treatment. If radioiodine
ferentiate follicular and parafollicular tumors. • An iodine-restricted diet and methimazole is a possibility, it is CRITICAL to NOT
were used in one dog to palliate clinical signs perform a contrast-enhanced CT because
TREATMENT of hyperthyroidism resulting from a thyroid doing so decreases treatment efficacy for at
mass. least 4 weeks.
Treatment Overview • If considering surgery, the most important
Optimal treatment depends on location and Possible Complications consideration is whether the tumor is
resectability, owner’s goals, and availability of • Thyroid tumors or their treatment (surgery attached to underlying structures.
RT. Most freely moveable tumors are resected. or RT) can cause laryngeal paralysis and
Invasive or attached tumors are surgically Horner’s syndrome. Technician Tips
cytoreduced to microscopic disease and then • Surgical removal of bilateral thyroid tumors • The jugular vein may be displaced. Shaving
treated with RT or treated with RT alone. can result in hypoparathyroidism and hair over the venipuncture site may be
hypocalcemia; if this is anticipated, consider helpful.
Acute Treatment perioperative calcitriol and calcium (p. 519). • Jugular venipuncture should not be per-
• In cases of severe respiratory compromise, • Hypothyroidism is expected with bilateral formed before CT or scintigraphy because
consider tracheostomy (p. 1166). thyroidectomy and is possible with definitive it can create artifact.
• Occasionally, dogs with functional tumors RT (p. 525).
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can experience a thyroid storm (i.e., sudden • Myelosuppression with high-dose I Client Education
release of excessive amounts of or exagger- • Owners must be prepared to manage endo-
ated response to thyroid hormone) that Recommended Monitoring crine complications of therapy for thyroid
causes acute tachycardia and hypertension. • Assessment of the neck (exam and possibly neoplasia, including accurate, timely, and
Treat symptomatically with supportive care ultrasound or CT) and lungs (thoracic lifelong administration of calcitriol and/or
(beta-blockers). radiographs) q 3 months. levothyroxine.
• For dogs with hyperthyroidism, methimazole • Monitor thyroid function (total T 4 and TSH) • Pulmonary metastasis tends to progress
is sometimes used. Suggested starting dose 1 month after definitive treatment and q 3-6 slowly, and dogs can still benefit from
is 5 mg q 8-12h, then adjusted to effect. months thereafter. treatment.
Because it is unknown whether this affects • Monitor CBC weekly for 4-6 weeks (until
radioiodine uptake in dogs, avoid if possible neutrophils have reached a nadir and then SUGGESTED READING
before radioiodine therapy. If used, consider recovered) after radioiodine therapy. Nadeau ME, et al: Evaluation of the use of chemo-
a minimum 3-day withdrawal before radio- therapy and other prognostic variables for surgically
iodine therapy (based on Society of Nuclear PROGNOSIS & OUTCOME excised canine thyroid carcinoma with and without
Medicine recommendation for humans). metastasis. Can Vet J 2011;52:994-998.
• Treat hypothyroidism if present (see below), • With no treatment, median survival time AUTHOR: Kim A. Selting, DVM, MS, DACVIM, DACVR
but NOT before radioiodine therapy because (MST) is 3 months; dogs with sublingual EDITOR: Ellen N. Behrend, VMD, PhD, DACVIM
it decreases iodine uptake. tumors can have long MST.
• Surgery
Chronic Treatment ○ Tumors contained within the thyroid
• Surgical excision alone if freely moveable gland capsule and freely moveable, MST
• Surgery plus RT: external beam, or if is 3 years.
preoperative scintigraphy showed uptake, ○ With extracapsular invasion, MST is 6-12
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postoperative I can be considered months.

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