Primary hypoparathyroidism in two horses

Abstract

Two Thoroughbred horses were presented with various clinical signs which included sweating, agitation, muscle twitching and synchronous diaphragmatic flutter. These signs were associated with profound hypocalcaemia. A diagnosis of primary hypoparathyroidism was made on the basis of low serum ionised calcium concentration, hyperphosphataemia and markedly reduced serum immunoreactive parathyroid hormone concentrations in the presence of normal renal function. Treatment with a combination of intravenous calcium and subsequently oral calcium, magnesium and a vitamin D analogue (dihydrotachysterol) for up to 65 days resulted in complete remission of clinical signs. Horse 1 was euthanased 12 months after the initial recognition of signs. Results of necropsy were unremarkable apart from an absence of detectable parathyroid tissue. Horse 2 returned to athletic activities while receiving only maintenance doses of oral calcium carbonate.

Hypocalcemia Caused by Primary Hypoparathyroidism in a 3-Month-Old Filly

“…Serum samples were frozen (−18°C) and shipped on ice for analysis. Serum intact PTH f in the filly was 8.4 pg/mL (reference range, 1.1–208 pg/mL by a human 2‐site immunochemiluminometric assay 1 ; 7.4–82.7 pg/mL in adult horses by a human intact PTH assay 2 ; 10.2–96.5 pg/mL in adult horses by a rat amino‐terminal assay 2 ; 9.2 ± 1.8 pg/mL in foals of 90‐days‐old by a human intact PTH assay, 3 and 32.8 ± 8.7 pg/mL in foals of 90 days old by a human whole PTH assay 3 ; 1,100–6,400 pg/mL by a human intact assay 4 ).…”

Electrolytes and Neurological Dysfunction in Horses

“…In adults, the prognosis for hypocalcemic seizures are more guarded. 40,44,56 Specific manifestations of ionized hypocalcemia in the horse include synchronous 276 Section III / Specific Disease Syndromes 41,42 Eclampsia (Lactation Tetany) 27,43 Idiopathic hypocalcemia of foals 44 Exercise-induced hypocalemia 45,46 Disease-states causing endotoxemia 47,48 Oxalate ingestion 49 Cantharadin toxicity 50 Acute renal failure 41 Pancreatic necrosis Colic and other GI disease [51][52][53] Transportation Transport Tetany Liver disease Iatrogenic bicarbonate overdose Furosemide administration 54 Sepsis 47,48 diaphragmatic flutter (thumps), whereby depolarization of the right atrium stimulates neuronal discharge of the phrenic nerve as it crosses over the heart. Clinically, this is observed as a rhythmic movement of the flank as a result of diaphragmatic contractions that are synchronous with the rhythm of the heart.…”

“…Clinically, this is observed as a rhythmic movement of the flank as a result of diaphragmatic contractions that are synchronous with the rhythm of the heart. 42,45 Excessive chloride ion losses in the horse can lead to an ionized hypocalcemia. Hypochloremic metabolic alkalosis leads to an increased binding of Ca ϩϩ to blood transport proteins (mainly albumin).…”

“…Excessive respiration and consequent respiratory alkalosis in these exercising horses can also contribute to the development of ionized hypocalcemia. 40,42,45 Lactation tetany (eclampsia) typically occurs in horses in the last 2-3 weeks of pregnancy and up to 5 days after weaning. Draft breeds appear to be overrepresented, however any mare producing large volumes of milk, eating a low-calcium ration or grazes lush pasture, and performs physical activity is at increased risk.…”

“…41 Secondary hypoparathyroidism has not been reported in the horse, however low PTH concentrations have been demonstrated in septic horses, attributed to a concurrent hypomagnesemia. 42 Inflammatory mediators in septic/endotoxemia shock may also contribute to reduced PTH release and subsequent hypocalcemia. [57][58][59][60] A complete understanding of the mechanisms of hypocalcemia in sepsis is still unclear.…”