Thyroid Neoplasia and Symptoms

Diarrhea can be a symptom related to various underlying health issues.
Thyroid neoplasia often presents in cats as mostly euthyroid, but with signs of dwarfism, a broad head, and short limbs.
Delayed dental eruption is a common sign of thyroid issues.
Less common symptoms include head tilt, incoordination, facial paralysis, and infertility.

Treatment efficacy can be determined by measuring TT4 levels; increased TT4 indicates a potential pituitary gland issue, while normal levels suggest a thyroid gland problem.
TRH stimulation testing is unreliable, often showing only a low increase in serum T4 levels.
Measuring TSH in response to TRH can help differentiate between primary and secondary hypothyroidism.

Radiographs are generally not useful for diagnosing congenital hypothyroidism, except for identifying specific skeletal abnormalities like epiphyseal dysgenesis and delayed ossification.
Megacolon is commonly associated with congenital hypothyroidism in cats.
Supportive treatment includes a y/d diet with low iodine to manage thyroid hormone production; not suitable for growing kittens or pregnant cats.

TT4 (total T4), fT4 (free T4), T3 (total triiodothyronine), and TSH (Thyroid Stimulating Hormone) are crucial for thyroid function assessment.
TT4 has high specificity (98-100%) and moderate sensitivity (90%), while fT4 is beneficial for determining thyroid status in cats with borderline total T4 levels.
T3 levels are typically elevated in hyperthyroid cases and useful when combined with other thyroid tests.

Radioiodine therapy (I-131) is the most effective treatment for hyperthyroidism, with a success rate exceeding 95%.
This treatment involves a single injection of radioactive iodine that condenses in the thyroid gland and destroys hyperactive tissue without the need for anesthesia or surgery.
Post-treatment, cats may need to stay at the treatment facility for 10-14 days until radioactivity levels in urine and feces are deemed safe.
T4 levels typically normalize within 4-12 weeks post-treatment, although thorough resolution of clinical signs may take several months.

I-131 has a physical half-life of 8 days; however, its biological half-life is shorter (1.5-4 days).
It emits both beta particles, responsible for tissue destruction, and gamma radiation, which poses minimal risks to adjacent structures.

Surgery: May appear costly but can be more affordable than years of oral medication and regular bloodwork. Post-surgery, cats typically become hypothyroid and require supplemental T4 orally.
Radioiodine Therapy (I-131): Considered the most effective treatment for hyperthyroidism. Administered via injection, it concentrates in the thyroid gland, destroying hyperfunctioning tissue with minimal side effects.
Treatment Duration: Cats may require hospitalization for 10–14 days for monitoring until radioactive levels in urine and feces decrease.
Success Rate: Over 95% success rate reported with a single 131I treatment, with T4 levels declining to normal within 4–12 weeks post-treatment. Complete resolution of clinical signs may take several months.
Radioactive Properties: The physical half-life of 131I is 8 days, while the biological half-life is shorter (1.5–4 days). It emits beta particles (mainly causing tissue destruction) and gamma radiation.

Symptoms of Dwarfism: Broad head, short neck, and limbs. Additional signs of delayed dental eruption.
Less Common Signs: Includes head tilt, incoordination, facial paralysis, and infertility.

TRH Stimulation Testing: Unreliable; typically results in low serum T4 increase. Testing TSH response to TRH can differentiate between primary and secondary hypothyroidism.
T4 Monitoring: Regular serum T4 levels should be measured monthly. If no significant improvement is seen within three months, reconsider the diagnosis of hypothyroidism.

Congenital Hypothyroidism Indicators:
- Epiphyseal dysgenesis
- Delayed ossification
- Shortened vertebral bodies
- Megacolon is commonly observed in congenital cases.

y/d Diet: A low-iodine diet used to reduce thyroid hormone production. Not suitable for growing kittens or pregnant cats.

TT4: Preferred test with high specificity (98-100%) for hyperthyroid cats.
fT4: Measurement of Free T4 helps determine status in cases of high-normal or borderline total T4 levels.
T3 Levels: Total T3 generally elevated in hyperthyroid cats, can be used alongside other thyroid tests.
TSH Levels: Helpful in assessing thyroid function.
Radiography and Ultrasound: Enlarged thyroid gland visualized on ultrasound, with radiographic imaging revealing characteristics of thyroid enlargement.
Thyroid Scintigraphy: Technetium-99m Pertechnetate uptake is compared in thyroid and salivary glands, with normal results indicating equal activity. Enlarged right thyroid gland suggests pathology.