Hyperparathyroidism (primary)
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Introduction Autonomous and excessive secretion of parathyroid hormone (PTH) Cause : tumor of parathyroid gland, usually adenoma - rarely carcinoma.Signs : associated with subsequent hypercalcemia, ie PU/PD.Diagnosis : laboratory data, histopathology.Treatment : parathyroidectomy.Prognosis : good following complete removal of affected parathyroid gland.Presenting signs Asymptomatic. Polyuria/polydipsia. Anorexia, vomiting. Muscle weakness. Age predisposition Middle age to old (mean 7 years). Breed predisposition Keeshund Predisposing factors General Four parathyroid glands in two pairs in cervical area. The caudal pair are embedded in thyroid tissue. In normal animal PTH is secreted in response to low [serum calcium] and results in:Reduced renal calcium excretion. Increased renal phosphate excretion. Increased gut uptake of calcium, via increased renal vitamin D activation. Bone resorption. Autonomous PTH secretion for an abnormal gland Pathophysiology Autonomous PTH secretion Timecourse (incubation, duration) Months. Animals often have long-term histories of vague illness. Presenting problems Hypercalcemia Normal or high parathyroid hormone levels Client history Polydipsia/polyuria. Lethargy. Inappetance, vomiting Diarrhea/constipation. Urinary tract signs. Seizures Clinical signs Usually normal but full examination MUST be performed to rule out other potential causes of hypercalcemia. Diagnostic investigation Hypercalcemia Normal or high parathyroid hormone levels Phosphate ALP Renal failure Renal architecture should be examined for the presence of calcium deposition Parathyroid ultrasonography has been attempted - normal glands cannot be seen but enlarged glands may be visualized. Surgical exploration of cervical area. Radiography Soft tissue mineralization with prolonged hypercalcemia. Osteopenia and occasionally pathological fractures in severe cases. Urinalysis Urine SG low Calcium-containing uroliths Changes associated with hypercalcemia:Short QT interval. Atrioventricular block Confirmation of diagnosis Discriminatory diagnostic features Clinical signs. Absence of any obvious cause of hypercalcemia. Definitive diagnostic features Results of PTH assay Response to parathyroidectomy. Histopathology findings Differential diagnosis Other causes of hypercalcemia:Malignancy (lymphoma Renal failure Hypoadrenocorticism Hypervitaminosis D Active lytic bony lesions. Initial symptomatic treatment All four parathyroid glands should be examined closely - disease may be single, unilateral or bilateral. Surgical parathyroidectomy should be curative. Ethanol and heart ablation have also been described. Animal should be stabilized prior to surgery (see treatment for hypercalcemia Intravenous saline. Diuresis (furosemide Prednisolone Monitoring Resolution of hypercalcemia within 2-3 days. Monitor renal function for early detection of any chronic renal failure Subsequent management Treatment Monitor for developing hypocalcemia and treat if necessary. Prognosis Excellent following successful parathyroidectomy. Expected response to treatment Calcium levels should return to normal within 2-3 days of surgery. Reasons for treatment failure Incorrect diagnosis (extra-parathyroidal cause of hypercalcemia). Inadequate excision of parathyroids. Publications Refereed papers Recent references from PubMed . Berger B & Feldman EC (1987) Primary hyperparathyroidism in dogs - 21 cases (1976-1986). JAVMA 191 , 350-356. Wisner E R, Nyland T G, Feldman E C, Nelson R W & Griffey S M (1993). Ultrasonographic evaluation of parathyroid glands in hypercalcemic dogs. Vet Radiol and Ultrasound 34 , 108-111. Vetstream contributor(s) Penney Barber BVM&S MRCVS , Department of Veterinary Basic Sciences, The Royal Veterinary College, University of London, Royal College Street, London NW1 0TU, UK.Dr David Bruyette DVM DipACVIM , VCA West Los Angeles, 1818 South Sepulveda Boulevard, Los Angeles, CA 90025, USA.
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CANIS DIS02423
hypercalcemia.
Parathyroid adenomas may be very difficult to differentiate from hyperplastic disease histologically.
Single parathyroid mass with atrophy of other glands