Hyperthyroidism Associated with a Thyroid Adenocarcinoma in a 21‐Year‐Old Gelding

Abstract

A riding was presented for evaluation of an enlarging mass in the right cervical region and weight loss of 8 months' duration. The mass had been present for approximately 2 years, but had been increasing in size over the last few months. The owner estimated that the gelding had lost approximately 90 kg. The owner also reported that the gelding had exhibited several episodes of tachypnea associated with anhidrosis over the last 2 weeks and had noted behavioral abnormalities manifested as pacing in the paddock and difficulty when handled.On presentation, the gelding was thin, but was bright and alert. On physical examination, a firm, oblong mass approximately 12 X 9 cm was palpated dorsolateral to the trachea, immediately caudal to the angle of the mandible. The mass was loosely attached and nonpainful. Based on location, the mass was suspected to be a neoplastic thyroid gland. Normal rectal temperature (37.6"C), and respiratory rate (20 breathslminute) were present. However, an intermittent mild tachycardia (48-56 beatdminute) that lasted several minutes and occurred at various times throughout the day was noted. No other abnormalities were noted on clinical examination.Results of CBC and serum biochemistry were within reference range. A homogenous mass that was interspersed with several areas of centrally located hypoechoic foci was observed ultrasonographically, using a 7.5-MHz linear transducer (Ausonics Opus 1, Ausonics, Sydney, Australia). This structure was consistent with the right thyroid gland. Cytologic examination of a fine-needle aspirate of the mass revealed a population of oval to round cells with indistinct cytoplasmic borders, marked anisokaryosis, and prominent nucleoli. Some cells contained darkly pigmented cytoplasmic granules. These changes were consistent with thyroid adenocarcinoma,' but histopathology was recommended for definitive diagnosis (Fig 1).Baseline serum total thyroxine (TT,) concentration measured by a commercially available radioimmunoassay (RIA) kit was 12.4 nmol/L (normal reference range: 8. concentration measured using a commercially available equilibrium dialysis and RIA kit was >126.1 pmol/L (normal reference range: 8.8-30.4 pmol/L; Free T4 by Equilibrium Dialysis, Nichols Institute Diagnostics, San Juan Capistrano, CA). Both assay kits had previously been validated for use in horses.' These results were compatible with a functional thyroid tumor. Treatment options included surgical thyroidectomy or radioactive thyroid ablation using '''1. Adjunct treatment with antithyroid drugs such as methimazole or propylthiouracil also was considered. Surgical resection of the mass was elected due to financial considerations and the limited use of these drugs in horses.The horse was anesthetized and maintained with isoflurane in oxygen, and placed in lateral recumbency with the head and neck extended. A 12-cm skin incision was made caudal to the ramus of the mandible and ventral to the linguofacial vein. Blunt dissection was used to expose the tumorous thyroid gland. The mass was smoot...

Influence of endemic goitre areas on thyroid hormones in horses

“…The effects of iodine deficiency in thyroid disorders, especially in endemic goitre areas, have been reported both in humans (Squatrito et al, 1981;Vigneri, 1988;Vermiglio et al, 1990;Vermiglio et al, 1995) and in different animal species (Hetzel and Mano, 1989;Maberly, 1994;Pugliese et al, 2007). Although diagnosis of thyroid disease in the horse is difficult (Frank et al, 2002;Messer and Johnson, 2007), cases of hypo- (Sojka, 1995;Breuhaus, 2002) and hyperthyroidism (Ramirez et al, 1998;Tan et al, 2008) in adult horses have been documented only rarely. Single measurements of T 4 and T 3 are difficult to interpret, particularly because thyroid hormone metabolism or transport can be affected by physiological or pathological states and by a variety of drugs (Breuhaus, 2002) as well as by the influence of circadian rhythm (Duckett et al, 1989;Komosa et al, 1990).…”

Tumors of the endocrine system in the horse - clinical pathology

“…Meist sind es Adenome (Hopper et al 1987), seltener Karzinome oder C-Zelltumoren (van der Velden und Meulenaar 1986, Dalefield und Palmer 1994, Bradley et al 2000. Die Metastasierungsneigung von SD-Karzinomen wird beim Pferd als niedrig eingeschätzt (Hillidge et al 1982, Ramirez et al 1998. In einigen Fällen ist jedoch eine Metastasierung in Lunge, Niere, Herz, seröse Häute, verschiedene Lymphknoten, die Skelettmuskulatur, Nebennieren, in das Auge und diverse Knochen (Humerus, Femur, Tibia, Os occipitale) beschrieben (Joyce et al 1976, von Häni et al 1979, Chiba et al 1987, Bradley et al 2000.…”

“…5 Klinische Befunde bei Pferden (n=8) mit Schilddrüsentumoren (OP-Produkte, Einsendungsmaterial) Clinical findings in horses (n=8) with thyroid gland tumors (surgery products, routine submissions) (Appleby 1976). Wäh-rend in der einschlägigen Literatur regelmäßig von Phäoch-romozytomen beim Pferd berichtet wird (Buckingham 1970, Gelberg et al 1979, Johnson et al 1995, sind nur Einzelfälle von equinen Neoplasien der NNR beschrieben (van der Kolk et al 1994, van der Kolk et al 2001 (Held et al 1985) oder Hyperthyreoidismus infolge von SD-Neoplasien (Ramirez et al 1998, Alberts et al 2000 berichtet. SD-Tumoren werden insbesondere bei älteren Pferden beschrieben; es handelt sich zumeist um Adenome, aus denen sich in Ausnahmefällen Adenokarzinome entwickeln können, wobei diese langsam wachsen und in der Regel nicht metastasieren, weshalb sie klinisch häufig nicht diagnostiziert werden (Dalefield und Palmer 1994 (Hoppen et al 2006, Durham 2010a, 2010b.…”

Unilateral thyroidectomy in 5 horses with thyroid tumors

“…Ultrasonographic image of a thyroid tumor with homogeneous appearance; T=tumor, white arrow=capsule. ist, dass es sich hier ausschließlich um Stuten handelte, obwohl aus der Literatur keine Geschlechtsprädisposition bekannt ist (Turk et al 1983, Patton et al 1985, Hovda et al 1990, Ramirez et al 1998, Alberts et al 2000, Elce et al 2003 Bei dem eigenen Patientengut wurde bei keinem der fünf Tiere durch den operativen Eingriff eine gleichseitige Kehlkopflähmung ausgelöst. Als mögliche Ursache hierfür wird die Tatsache angesehen, dass bei dem Eingriff die locker im Bindegewebe eingebettete Schilddrüse intra operationem durch den Operateur weit nach ventral gedrückt wurde.…”

“…Klinisch treten in der Regel, außer einer vergrößerten Schilddrüse, keine weiteren klinischen Symptome auf (Hopper et al 1987, Elce et al 2003. Allerdings wurde auch über Anzeichen für einen Hyperthyreoidismus bei einem Quarter-Horse mit einem Schilddrüsenadenom (Alberts et al 2000) sowie bei einem Araber-Wallach mit einem Adenokarzinom der Schilddrüse (Ramirez et al 1998) berichtet.…”