Lumbar vertebral bone density is decreased in horses with pituitary pars intermedia dysfunction.
Authors: Colbath Aimee C, Fortin Jessica S, Burglass Caroline M, Panek Char, Vergara-Hernandez Fernando B, Johnson Tyler N, Robison Cara A, Logan Alyssa A, Nelson Nathan A, Nielsen Brian D, Schott Harold C
Journal: Equine veterinary journal
Summary
Pituitary pars intermedia dysfunction (PPID) has been anecdotally linked to pathological fractures in horses, yet the underlying bone changes remain poorly characterised. Researchers from this 2024 study examined bone mineral density (BMD) across weight-bearing and non-weight-bearing skeletal sites in five PPID-affected horses compared with aged and young controls, utilising quantitative computed tomography and biomechanical testing of lumbar vertebrae post-mortem, alongside serum markers of bone metabolism. The most striking finding was a significant reduction in both trabecular and cortical BMD in the third, fourth and fifth lumbar vertebrae of PPID+ horses relative to both aged controls (p<0.001) and young controls (p<0.01); conversely, weight-bearing bones (third metacarpus and metatarsus) showed no density changes between groups, and biomechanical properties of the fourth lumbar vertebra remained comparable between PPID+ and aged horses. Serum concentrations of parathormone, ionised calcium, 25-hydroxyvitamin D and osteocalcin did not differ significantly, suggesting the vertebral bone loss occurs through mechanisms independent of conventional calcium-phosphate or vitamin D homeostasis. These findings propose a site-specific vulnerability in non-weight-bearing axial skeleton in PPID-affected horses that may predispose to vertebral fractures—a clinically important consideration for practitioners evaluating chronic lameness, performance decline or back pain in older horses with suspected PPID.
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Practical Takeaways
- •PPID horses may be at increased risk of vertebral fractures and pathological fractures of non-weight-bearing bones despite normal gait and performance, warranting radiographic monitoring of the spine
- •Standard biochemical markers (calcium, vitamin D, PTH) may not reflect bone quality changes in PPID horses, so BMD assessment via CT or similar imaging should be considered in clinical evaluation
- •Farriers and handlers should be aware that PPID+ horses may have compromised vertebral integrity that is not apparent clinically, particularly relevant when backing young horses or those with recent PPID diagnosis
Key Findings
- •Trabecular and cortical bone mineral density of lumbar vertebrae (L3, L4, L5) was significantly lower in PPID+ horses compared to both aged and young PPID- controls (p<0.001 and p<0.01 respectively)
- •No differences in BMD were found in weight-bearing bones (third metacarpus and third metatarsus) between PPID+ and control horses
- •No differences in biomechanical properties (fracture force, displacement, Young's modulus, strain) were detected between PPID+ and aged PPID- horses despite reduced BMD
- •Serum biomarkers (PTH, ionized calcium, 25-hydroxyvitamin D, osteocalcin) showed no significant differences between groups despite BMD differences