ISSN 2398-2985      

Hyperthyroidism

Jreptile

Introduction

  • Cause: excessive secretion of thyroid hormones by the thyroid gland. 
  • Signs:
    • Dysecdysis and decreased/increased frequency of shedding (snakes).
    • Polyphagia.
    • Weight loss.
    • Loss of dorsal spines.
    • Hyperactivity.
    • Tachycardia.
    • Increased aggression.
    • Palpable thyroid gland (goiter).
    • Anorexia.
    • Diarrhea.
    • Bleeding from mouth.
    • Intra-oral mass.
    • Increased frequency of shedding (lizards).
    • Post-mortem finding (snakes, lizards and chelonia).
  • Diagnosis: elevated serum total t4 (measured by radioimmunoassay in snakes), ultrasound examination, fine-needle aspiration, technetium scan, CT scan.
  • Treatment: thyroidectomy, carbimazole (snakes), radioactive iodine treatment (lizards).
  • Prognosis: unknown.

Pathogenesis

Etiology

Thyroid levels are affected by temperature, season, sex, age, nutritional status and photoperiod. The normal ranges of thyroid enzymes are poorly researched for the wide variety of reptile species seen in practice.
  • Thyroid glands affected with hyperplasia, adenoma, and carcinoma may secrete excessive thyroid hormones: thyroxine T4 and triiodothyronine T3.
  • Ante-mortem diagnosis uncommon.
  • Adenomas have been reported in the Green iguana Green iguana, Crocodile lizards, Komodo dragon, Dumerill’s ground boa, Everglades rat snakes, Gopher snake, Chaco tortoise, Desert tortoise, Freshwater turtle, Stinkpot turtle.
  • Carcinomas have been reported in a Crocodile lizard, Painted turtle, Indian black turtle, Red-eared slider (terrapin) Red-eared slider.
  • Multicentric lymphoblastic lymphoma involving the thyroid glands in a loggerhead sea turtle.
  • Relatively elevated T4 levels have been reported in Leatherback turtles entangled in fishing gear.

Pathophysiology

Timecourse

  • Depends on thyroid gland pathology.

Epidemiology

  • Prevalence rare in reptiles.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Pajdak-Czaus J, Terech-Majewska E, Będzłowicz D et al (2019) Applicability of thyroxine measurements and ultrasound Imaging in evaluations of thyroid function in turtles. J Vet Res 63 (2), 267-273 PubMed
  • Hunt K E, Innis C J, Merigo C & Rolland R M (2016) Endocrine responses to diverse stressors of capture, entanglement and stranding in leatherback turtles (Dermochelys coriacea). Conservation Physiology 4 (1), cow022 PubMed.
  • Hadfield C A, Clayton L A, Clancy M M, Beck S E, Mangus L M & Montali R J (2012) Proliferative thyroid lesions in three diplodactylid geckos: Nephrurus amyae, Nephrurus levis and Oedura marmorata. J Zoo Wildl Med 43 (1), 131-140 PubMed.
  • Gal J, Csikó G, Pásztor I, Bölcskey-Molnár A & Albert M (2010) First description of papillary carcinoma in the thyroid gland of a red-eared slider (Trachemys scripta elegans). Acta Vet Hung 58 (1), 69-73 PubMed.
  • Rivera S & Lock B (2008) The reptilian thyroid and parathyroid glands. Vet Clin North Am Exot Anim Pract 11 (1), 163-75 PubMed.
  • Greenacre C B, Young D W, Behrend E N & Wilson G H (2001) Validation of a novel high sensitivity radioimmunoassay procedure for measurement of total thyroxine concentration in psittacine birds and snakes. AJVR 62 (11), 1750-1754 PubMed.
  • Hernandez-Divers S J, Knott C D & MacDonald J (2001) Diagnosis and surgical treatment of thyroid adenoma-induced hyperthyroidism in a green iguana (Iguana iguana). J Zoo Wildl Med 32, 465-475 PubMed.
  • Orós J, Torrent A, Espinosa de los Monteros A et al (2001) Multicentric lymphoblastic lymphoma in a loggerhead sea turtle (Caretta caretta). Vet Pathol 38 (4), 464-467 PubMed.
  • Whiteside D P & Garner M M (2001) Thyroid adenocarcinoma in a crocodile lizard, (Shinisaurus crocodilurus). J Herpetol Med Surg 11 (1), 13-16 VetMedResource.

Other sources of information

  • BSAVA Manual of Reptiles (2019) 3rd edn. Ed: Girling S & Raiti P. BSAVA, UK. 
  • Exotic Animal Formulary (2018) 5th edn. Ed: Carpenter J. Elsevier, USA. 
  • Pignon C (2013) Hyperthyroidism. In: Clinical Veterinary Advisor Birds and Exotic Pets. Eds: Mayer J & Donnelly T M. Elsevier, USA. pp 260-261.
  • Boyer T H & Steffes Z J (2011) Reptilian Thyroid Anatomy, Physiology and Disease. In: Proc Association of Reptilian and Amphibian Veterinarians ARAV.
  • Boyer T H, Wallack S, Bettencourt A & Bourdon M (2010) Hyperthyroidism in a Leopard Gecko, Eublepharis Macularius, and Radioiodine (I-131) Treatment. In: Proc ARAV. pp 111.
  • McArthur S, Wilkenson R & Meyer J (2004) Medicine and Surgery of Tortoises and Turtles. Blackwell Publishing, UK.
  • Kölle P & Hoffman R (2002) Thyroid Adenoma in a Stinkpot (Sternotherus Odoratus). In: Proc EAZW. pp 71-72.
  • Frye F (1991) Biomedical and Surgical Aspects of Captive Reptile Husbandry, Ch 5 Pathological conditions related to the captive environment p176-177. 2nd edn, Volumes 1 and 2. Krieger, USA.

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