Primary Hyperparathyroidism Associated With Atypical Headshaking Behavior in a Warmblood Gelding.
Authors: Schwarz Bianca, Klang Andrea, Schwendenwein Ilse
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Primary Hyperparathyroidism and Atypical Headshaking in an Equine Case A 14-year-old Warmblood gelding presenting with headshaking, lethargy, lameness in multiple limbs, back problems and recurrent colic episodes was investigated for persistent hypercalcaemia (4.8 mmol/L; normal 2.0–3.2 mmol/L) documented over 18 months. Through systematic exclusion of common causes of elevated blood calcium—renal failure, vitamin D toxicosis, granulomatous disease and secondary nutritional hyperparathyroidism—combined with diagnostic findings of hypophosphataemia (0.4 mmol/L; normal 0.5–1.3 mmol/L), low fractional urinary calcium excretion, and paradoxically elevated PTH secretion unresponsive to hypercalcaemia, primary hyperparathyroidism was confirmed. Although postmortem examination revealed no obvious parathyroid pathology, the clinical and biochemical profile was diagnostic. Primary hyperparathyroidism remains a rare diagnosis in equine medicine, yet practitioners should regard any sustained hypercalcaemia as abnormal and investigate systematically; this case highlights how an endocrine disorder can manifest as behavioural and locomotor dysfunction rather than classical signs. The atypical presentation—particularly headshaking as a neurological manifestation of mineral dysregulation—warrants awareness amongst farriers, veterinarians and rehabilitation specialists evaluating horses with seemingly unrelated or multi-system complaints, especially when lameness and behavioural issues cluster without obvious orthopaedic or musculoskeletal explanation.
Read the full abstract on PubMed
Practical Takeaways
- •Hypercalcemia is always abnormal in equine patients and warrants systematic investigation; primary hyperparathyroidism should be included in differential diagnoses alongside more common causes like renal disease and malignancy.
- •Atypical neurological presentations such as headshaking combined with chronic lameness, back pain, and recurrent colic may indicate metabolic disease—consider measuring serum calcium, phosphate, and PTH concentrations as part of diagnostic workup.
- •When hypercalcemia is confirmed, perform fractional excretion studies of calcium and phosphorus and measure PTH to distinguish primary hyperparathyroidism from other etiologies, as treatment options and prognosis differ significantly.
Key Findings
- •A 14-year-old Warmblood gelding presented with persistent hypercalcemia (4.8 mmol/L; normal 2.0-3.2) and headshaking behavior associated with primary hyperparathyroidism.
- •Primary hyperparathyroidism was diagnosed based on hypercalcemia, hypophosphatemia (0.4 mmol/L; normal 0.5-1.3), low fractional excretion of calcium, and high fractional excretion of phosphorus with PTH refractory to high calcium levels.
- •Other causes of hypercalcemia including renal failure, vitamin D toxicosis, granulomatous disease, and malignancy were systematically ruled out.
- •Postmortem examination was unremarkable, suggesting primary hyperparathyroidism is a rare but treatable differential diagnosis in horses with unexplained hypercalcemia and neurological signs.