Successful Detection and Removal of a Functional Parathyroid Adenoma in a Pony Using Technetium Tc 99m Sestamibi Scintigraphy

A 20-year-old, 275-kg, Welsh pony gelding was referred to New Bolton Center for treatment of primary hyperparathyroidism. The horse was diag- nosed with primary hyperparathyroidism based on persistently high total (19.5 mg/dL; reference range 10.8–13.5 mg/dL) and ionized serum calcium (9.36– 13.16 mg/dL; reference range 6–7.6 mg/dL) concentra- tions with concurrently increased serum parathyroid hormone (PTH) concentration (Immunoradiometric assaya) (128.63 pmol/L; reference range 0.60–11.00 pmol/L), and lack of evidence of renal failure (serum creatinine concentration, 1.7 mg/dL; reference range 0.8–2.2 mg/dL). Hypercalcemia was first identified 19 months earlier (total serum calcium concentration, 14.6 mg/dL; reference range 10.4–12.9 mg/dL), but was not accompanied by clinical signs until 3 weeks before presentation when lethargy and inappetence were noted. The gelding had been previously diag- nosed with pituitary pars intermedia dysfunction (PPID) and was being treated with pergolideb (1 mg PO q24h). The pony had no reported lameness prob- lems, other than a mild bout of laminitis presumably associated with PPID. No treatment for hypercalcemia was initiated before referral.