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

## TL;DR

This study found that dogs with spinal disc herniations show reduced muscle density near the injury site, detectable via CT scans, which could help assess spinal conditions.

## Contribution

The study introduces CT-based muscle attenuation as a potential biomarker for spinal pathology in dogs.

## Key findings

- Dogs with spinal injuries had lower muscle HU at the lesion site compared to controls.
- Older dogs and French Bulldogs showed lower overall muscle HU.
- A logistic regression model using HU changes correctly classified ~70% of cases.

## Abstract

Computed tomography (CT) can quantify muscle composition in dogs by measuring tissue density in Hounsfield units (HU). Lower HU indicates fattier or less dense muscle. This study compared lumbar epaxial muscle attenuation between dogs with thoracolumbar spinal disc herniations to that of healthy control dogs. Dogs with spinal injuries had lower muscle HU at the site of the lesion (suggesting acute muscle degeneration) compared to controls, whereas their muscle HU farther away from the lesion remained closer to normal. Control dogs had uniform muscle HU along the spine. We also noted that older dogs and certain breeds (like French Bulldogs) tended to have lower muscle HU. These findings suggest that CT assessment of paraspinal muscles may provide additional information about the presence and duration of spinal conditions in dogs.

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, p < 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, p = 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.