- Chronic right hindlimb lameness that had been previously localized to the proximal metatarsus by the referring veterinarian.
- Radiographs, ultrasound, and MRI of the right proximal metatarsal region were unremarkable. The distal tarsal joints had been injected but improvement in the lameness was temporary.
- Two and a half months after the MRI exam, the right hindlimb lameness returned in addition to a significant right forelimb lameness. Attempts at diagnostic analgesia by the referring veterinarian were unrewarding. The horse was referred for a whole-body nuclear scintigraphy study at that time.
Physical Exam and Lameness Findings
- On physical and lameness exams prior to nuclear scintigraphy, the horse had a grade III/V lameness on the right forelimb and a grade II/V lameness on the right pelvic limb. There was a mild right gluteal atrophy.
On nuclear scintigraphy, focal regions of moderate to severe IRU were identified in the following locations:
- Diffusely throughout the right and left humeri
- Right and left proximal radii
- Proximal aspect of the right third metacarpal bone
- Right mid-femoral diaphysis and left distal femoral condylar region
- Left proximal and distal tibia
- Right distal calcaneous/proximal tarsal bones
- Mid-diaphysis of the right third metatarsal bone
- The left mandible
Radiographs of the left distal tibia/tarsus were acquired because subjectively, the region had the greatest IRU and is easily radiographed.
A focal region of mild patchy sclerosis was identified within the dorsal aspect of the left distal tibia. The remainder of the radiographic projections were unrewarding.
The horse was prescribed four weeks of stall rest followed by gradual return to exercise. Gabapentin was prescribed for the first month following imaging.
At recheck approximately 4.5 months later, there was residual lameness in the right forelimb but the horse was overall greatly improved compared to the previous exam.
A follow-up whole body nuclear scintigraphy study was performed, at which point there was partial or near complete resolution of the majority of the previously identified lesions. Similar IRU was present within the mid-diaphysis of the right third metatarsal bone and new IRU (moderate to severe) was within the proximal aspect of the left third metacarpal bone and the left hind fourth metatarsal bone.
As lameness tends to be correlated with the degree of radiopharmaceutical uptake, particularly in the humeri, the partial improvement in the lameness in this patient may correspond to the resolution of many of the originally identified lesions. Due to the tendency for new lesions to appear, sometimes in different anatomic locations, the prognosis for athletic soundness is unknown.
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Ahern, Benjamin J., et al. “Enostosis-like Lesions in Equids: 79 Cases (1997–2009).” Journal of the American Veterinary Medical Association, vol. 245, no. 9, 2014, pp. 1042–1047.
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