A review of equine primary hyperparathyroidism

The identification of hypercalcaemia and hypophosphataemia on routine blood testing of mature horses with non-specific illness points to underlying primary hyperparathyroidism, an uncommonly encountered equine endocrinopathy. Diagnosis of primary hyperparathyroidism is established by ruling out other more likely explanations for hypercalcaemia, such as chronic kidney disease and cancer, and demonstrating that the patient's circulating parathyroid hormone level is inappropriately high. If an abnormal parathyroid gland can be identified, parathyroidectomy is usually curative. Ultrasonography and 99mTechnetium-sestamibi scintigraphy are instrumental for parathyroid gland targeting in equines. Left untreated, affected equids have lived with signs of lowered body condition, inappetence, lethargy and lameness for several years. In some cases, primary hyperparathyroidism is identified based on results of routine plasma biochemistry in the absence of evident clinical abnormalities. However, chronic hyperparathyroidism leads to generalised osteopenia with an increased risk of catastrophic fracture. Facial and nasal bone remodelling (fibrous osteodystrophy) associated with persistently elevated parathyroid hormone influence causes airway obstruction and increased difficulty in breathing. This article summarises current understanding of primary hyperparathyroidism and presents diagnostic guidelines and aspects of its treatment and management.