Thoracolumbar meningeal fibrosis in pugs

Abstract

Background: Thoracolumbar myelopathies associated with spinal cord and vertebral column lesions, with a similar clinical phenotype, but different underlying etiologies, occur in pugs.

Objectives: To further characterize the clinical and neuropathological characteristics of pugs with longstanding thoracolumbar myelopathy.

Animals: Thirty client-owned pure-bred pugs with a history of more than a month of ataxia and paresis of the pelvic limbs, suggesting a myelopathy localized to the thoracolumbar spinal cord, were included in the study.

Methods: Prospective clinicopathological study. Included pugs underwent a complete neurological examination and gross and histopathologic postmortem studies with focus on the spinal cord. Computed tomography (n = 18), magnetic resonance imaging (n = 17), and cerebrospinal fluid analysis (n = 27) were performed before or immediately after death.

Results: Twenty male and 10 female pugs had a median age at clinical onset of 84 months (interquartile range, 66-96). Affected pugs presented with a progressive clinical course and 80% were incontinent. There was circumferential meningeal fibrosis with concomitant focal, malacic, destruction of the neuroparenchyma in the thoracolumbar spinal cord in 24/30 pugs. Vertebral lesions accompanied the focal spinal cord lesion, and there was lympho-histiocytic inflammation associated or not to the parenchymal lesion in 43% of the pugs.

Conclusions and clinical importance: Meningeal fibrosis with associated focal spinal cord destruction and neighboring vertebral column lesions were common findings in pugs with long-standing thoracolumbar myelopathy.

Keywords: ataxia; meninges; spinal cord.

Figure 1

Distribution of the focal thoracolumbar spinal cord lesions and their adjacent vertebral malformations, diagnosed by computed tomography, in 17 pugs with long‐standing thoracolumbar myelopathy. Vertebral malformations included hemivertebra, hypo‐ or aplasia of the caudal articular process, and thoracolumbar transitional vertebrae. Blue bars represent focal spinal cord lesions. Red bars represent vertebral malformations

Figure 2

Transversal T2W spinal cord magnetic resonance images at the level of T10‐T11 in a pug. A ventrolateral subarachnoid diverticula (SAD) (A) is located immediately cranial to the intramedullary T2W hyperintensity (B). White arrow points at SAD in (A), at T2W hyperintensity in (B)

Figure 3

Histopathologic findings in the spinal cord from pugs affected by thoracolumbar myelopathy, showing: A, focal spinal cord lesion with segmental subdural fibrosis and adjacent slices without the fibrosis only a few millimeter cranially (CR) and caudally (CA) from the damaged area along the spinal cord; HE staining. B, Severe meningeal fibrosis with adhesion of lepto‐ and pachymeninges (asterisks). “D” indicates dorsal tract; Azan staining. C, Formation of diverticula with multiple compartments “C” of the subarachnoid space. “D” indicates dorsal tract; HE staining. D, Focal malacia with almost total destruction of the spinal cord, leptomeningeal (arrowheads) and subdural (asterisk) fibrosis with focal adhesions (arrow) and numerous arachnoidal diverticula (AD). HE staining. E, Myelin loss in the fasciculus gracilis (FG), of the dorsal funiculus, at the level of the cervical spinal cord; Luxol fast blue staining. F, Compression radiculopathy at T7. Note the enlarged transsectional diameter (blue dotted bracket) of preganglionic dorsal root (PGDR) in relation to the maximal dorsoventral diameter of the respective spinal cord segment (black dotted bracket). The most affected dorsal root further shows endoneurial oedema (blue‐lined asterisk). Both extradural parts of PGDR and ventral root (VR) present with thickening of the periradicular sheath (PRS), whereas intradural ventral rootlets are affected by a focal endoneurial fibrosis (EF), HE staining. G, Perivascular fibrosis (arrows) at the level of L3, spinal cord; Azan staining. H, Mild perivascular lympho‐histiocytic inflammation (arrows) in the cerebrum; HE staining. I, Moderate lympho‐histiocytic inflammation (arrows) in the spinal cord; HE staining. J, Moderate lympho‐histiocytic leptomeningitis (arrows) adjacent to a thoracic, malacic, focal spinal cord (SC) lesion. “X” represent pachymeninges; HE staining. K, Lack of leptomeningeal fibrosis (arrowheads) adjacent to a focal malacic cervical spinal cord lesion (*) in the dorsal horn. “D” represents dorsal tract; HE staining

Figure 4

Protrusion of chondroid tissue of the nucleus pulposus into the adjacent endplate, a so‐called Schmorl's node (arrowheads), in a pug. VE, vertebral endplate; *, intervertebral disc; HE staining