Evaluation of Attenuation of Lumbar Epaxial Musculature in Dogs with Spinal Pathology.

This study evaluated attenuation values of lumbar epaxial musculature in dogs with acute spinal pathology using computed tomography (CT) and compared them with values in dogs without spinal disease. Sixty client-owned dogs were included: thirty dogs with thoracolumbar spinal lesions (intervertebral disc herniation) and thirty control dogs without spinal abnormalities. Mean Hounsfield unit (HU) values of epaxial muscles (multifidus-longissimus-iliocostalis group) were measured bilaterally at three lumbar levels for each dog-one level cranial to the lesion, the lesion level, and one level caudal to the lesion; for controls, the corresponding segments were T13, L1, L2, and L3. Dogs with spinal pathology showed a significant local decrease in muscle HU at the lesion site (average 48 HU) compared to the segment cranial to the lesion (50-51 HU, < 0.01). In contrast, control dogs had relatively uniform muscle HU (~52-54 HU) across T13-L3 with no significant differences between these levels. Side to side differences were minimal in both groups. A logistic regression using the HU drop between segments correctly classified ~70% of cases, indicating moderate diagnostic value. Age and breed influenced overall muscle HU; older dogs had lower values (r = -0.39, = 0.03 in controls), and French Bulldogs showed lower HU than other breeds. In conclusion, dogs with acute thoracolumbar disc herniation exhibit a focal reduction in paraspinal muscle HU at the lesion level. This acute change is subtle but detectable with CT and may serve as an additional indicator of lesion presence or chronicity, although its clinical utility requires further investigation in larger studies.