Sara Longo 1, Sergio A Gomes 1, Chiara Briola 2, Katherine Duffy 3, Mike Targett 3, Nick D Jeffery 4, Paul Freeman 2

Background
Thoracolumbar intervertebral disc extrusion (IVDE) is a frequent cause of spinal cord injury in dogs. Although MRI is recognized as the gold standard for diagnosing disc degeneration, its role in predicting late clinical recurrence of IVDE has not been established. The study investigates the correlation between MRI-assessed disc degeneration and the likelihood of late recurrence in dogs surgically treated for thoracolumbar IVDE.

Methods
This retrospective study included 92 dogs treated via hemilaminectomy for thoracolumbar IVDE at two referral hospitals, with no prophylactic disc fenestration performed. MRI scans from T10 to L3 were evaluated for disc degeneration, classifying discs as nondegenerate, partially degenerate, or completely degenerate based on T2-weighted signal intensity. Follow-up was conducted via medical records and owner or referring veterinarian interviews to detect clinical recurrence, defined as signs suggestive of IVDE occurring at least eight weeks postoperatively.

Results
Of the 92 dogs, 33 (36%) exhibited late recurrence of clinical signs, with the presence of at least one completely degenerate disc significantly associated with recurrence (hazard ratio 2.92). Completely degenerate discs were more frequently found in the recurrence group (67%) than the nonrecurrence group (37%). MRI follow-up in a subset confirmed recurrence sites often corresponded to previously identified degenerate discs. Most recurrences were mild, and few underwent repeat imaging or surgery.

Limitations
Limitations include the retrospective nature, nonstandardized imaging protocols, reliance on low-field MRI, and variability in confirmation of recurrence (only partially supported by diagnostic imaging). The study also lacked uniform follow-up duration and excluded cases with early recurrence or grade 5 neurologic deficits.

Conclusions
The presence of a completely degenerate disc on MRI at the time of initial surgery is a significant risk factor for late recurrence of clinical signs in dogs with thoracolumbar IVDE. These findings support considering prophylactic fenestration of degenerate discs during initial surgery to potentially reduce recurrence risk.

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