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Line 81: Polyphagia and weight loss are two concurrent symptoms that have multiple causes, including: [[Diabetes in cats|diabetes mellitus]], [[malnutrition]], [[malabsorption]], and [[maldigestion]]. If these symptoms occur serum thyroxine levels should be tested to confirm or exclude a diagnosis of hyperthyroidism.<ref name="endo"/> ==Treatment== Hyperthyroidism can be either managed with [[anti-thyroid]] drugs or restricting [[iodine]] intake, or it can be treated with [[radioactive iodine]] or [[thyroidectomy]] for a permanent solution. Choice of treatment depends on a multitude of factors including cost, availability of the treatments, and age and health of the patient. In areas where available, radioactive iodine treatment is the preferred method of treating hyperthyroidism due to the low risks and high efficacy.<ref name="endo"/> ===Surgery=== Surgery is a cheaper option than radioactive iodine treatment and does not require any equipment not found in a standard veterinary clinic. It also results in a quicker decrease in thyroid hormone levels. Surgery however can be more risky to elderly cats given the increased risk of [[anaesthetic]] complication. A bad surgery can result in nerve damage or fail to fully remove all the abnormal tissue. It may also result in [[iatrogenic]] [[Hypothyroidism in dogs#Cats|hypothyroidism]] and [[hypoparathyroidism]].<ref name="endo"/> Line 116: Carbimazole is quickly transformed to methimazole after absorption or in the gastrointestinal tract. No studies compare the two but evidence suggests lower rates of adverse effects with no reports of severe blood disorders.<ref name="endo"/> ===Radioactive iodine=== [[Radioactive iodine]] treatment results in quick decrease of thyroid hormone, does not require any anaesthetic or surgery, and in most cases is a single treatment. The disadvantages of radioactive iodine is the cost, the availability of it, and the local period a cat needs to stay in a specialised hospital as the radioactivity wears off. The success rate of radioactive iodine treatment is very high at around 95%. Radioactive iodine is administered either [[intravenous]]ly or [[Subcutaenous injection|subcutaneous]]ly. The iodine gets transported to neoplastic and hyperplastic thyroid tissue. 40–90% of the iodine is excreted via defecation and urination. [[Gamma ray]]s and [[beta particile]]s are emitted and these particles cause [[Thyroid follicular cell|follicular cell]]s to die off. The beta particles do not affect the [[parathyroid gland]] or any other part of the body due to their movement being limited to less than 2mm. The [[atrophied]] thyroid tissue will return to regular production of thyroid hormone which avoids the risk of iatrogenic hypothyroidism with other treatment options.<ref name="endo"/> In one study after 4 years 84% of cats were euthyroid and 4% were hypothyroid.<ref>{{cite journal | last=Théon | first=Alain P. | last2=Van Vechten | first2=Melinda K. | last3=Feldman | first3=Edward | title=Prospective randomized comparison of intravenous versus subcutaneous administration of radioiodine for treatment of hyperthyroidism in cats | journal=American Journal of Veterinary Research | volume=55 | issue=12 | date=1994-12-01 | issn=0002-9645 | doi=10.2460/ajvr.1994.55.12.1734 | pages=1734–1738}}</ref> Thyroid carcinomata are uncommon but difficult to diagnose and require higher dosage to treat. [[Necrosis]] may occur following treatment if there is a lot of neoplastic tissue. This risk can be mitigated with surgery, although surgery itself carries risk. High radiation dosage often results in permanent hypothyroidism.<ref name="endo"/> ===Iodine intake=== Limiting the iodine intake of a hyperthyroid cat is a cheap and easy way to manage hyperthyroidism and can be done by the owner with ease; however, it is not always effective, cats may refuse food or find other sources of iodine. The long term effects of this treatment are not currently known.<ref name="endo"/> | |||