Thoracolumbar myelopathies in pug dogs

Abstract

Background: Constrictive myelopathy (CM) involving a fibrous band around the spinal cord is a newly recognized disease in pug dogs.

Objectives: To identify the frequency of CM based on diagnostic imaging supplemented with necropsy; to determine whether a relationship exists between the sites of CM and other described T3-L3 myelopathies; and to determine the frequency of caudal articular process dysplasia (CAPD).

Animals: Thirty-two client-owned pug dogs diagnosed with a chronic, progressive T3-L3 myelopathy based on neurological examination performed by a board-certified neurologist.

Methods: This is a prospective study. All dogs underwent computed tomography (CT) and magnetic resonance imaging (MRI) reviewed by a board-certified radiologist. Magnetic resonance imaging abnormalities were categorized into diseases; CM only, CM plus other non-CM condition(s), or non-CM condition. Sites of CAPD were reported on CT. Nineteen dogs underwent necropsy.

Results: Magnetic resonance imaging revealed 3 dogs with CM only, 17 with CM plus at least 1 other myelopathy, 11 dogs with non-CM myelopathies only, and 1 with no MRI abnormalities. Nineteen of 32 dogs had >1 myelopathy diagnosis on MRI whereas 15/32 had >1 site of spinal cord compression. All dogs had CAPD at >1 site in the T3-L3 vertebral column on CT.

Conclusions and clinical importance: Constrictive myelopathy affected more than half of pug dogs presenting with chronic thoracolumbar myelopathies. Most had multilevel disease, concurrent myelopathies, or both. There was no apparent relationship between anatomic locations of CAPD and most severe myelopathy or myelopathy type.

Keywords: chronic; constrictive myelopathy; meningeal fibrosis; thoracolumbar arachnoid fibrosis.

FIGURE 1

(A) Sagittal T2‐weighted magnetic resonance (MR) image of the thoracolumbar region displaying a hypointense ventral and dorsal spinal cord compression and focal spinal cord atrophy at the level of T12‐T13 indicated by the arrows. (B) Transverse T1‐weighted fat saturated postcontrast MR image of the same dog at level of T12 displaying a hypointense band of tissue predominantly dorsolateral to the spinal cord. There is contrast enhancement of the ventrolateral meninges and spinal cord atrophy at this location indicated by the asterisk.

FIGURE 2

Bar graph representing total number of each myelopathy present in all pug dogs in this study. While caudal articular process dysplasia (CAPD) was present in all studied dogs, constrictive myelopathy (CM) and intervertebral disc herniation (IVDH) were the most frequently encountered compressive myelopathy on neuroimaging. No dogs had CM and subarachnoid diverticulum (SAD) combined, nor SAD alone.

FIGURE 3

Bar graph displaying number of pug dogs diagnosed with 1 type of compressive spinal cord disease or multiple types of disease. There was 1 dog diagnosed with no spinal cord lesions visible on magnetic resonance imaging. Caudal articular process dysplasia was present in all dogs and is not presented in this figure.

FIGURE 4

Graphical representation of vertebral segments affected by caudal articular process dysplasia (CAPD) (blue) and myelopathies (red). The discrepancy between the CAPD frequency in the mid‐ to caudal thoracic region, and predominance of non‐CAPD myelopathies in the caudal thoracic to cranial lumbar region, makes an association in pathogenesis less likely. Note that the vertebral segments indicate CAPD of the caudal articular process of the cranial listed vertebra, for example, T9‐T10 refers to caudal articular process of T9. The caudal‐most thoracic vertebra in a few dogs was transitional (with a vestigial rib on 1 side or both sides), we elected to call the caudal‐most joint “last thoracic to L1.”

FIGURE 5

(A) A ×10 photomicrograph of a transverse section of spinal cord stained with hematoxylin and eosin (H&E) displaying a dorsal thickening of the arachnoid layer (A) of the meninges by fibrous tissue. (B) A ×100 photomicrograph of a transverse section of spinal cord stained with H&E demonstrating a detailed look at the arachnoid fibrosis (A). DM, dura mater; GM, gray matter; PM, pia mater; SC, spinal cord; WM, white matter.