AFIP Systemic Pathology

JPC SYSTEMIC PATHOLOGY

Nervous System

January 2017

N-M03

 

Signalment (JPC 1533450):  Three-year-old great Dane

 

HISTORY:  This dog was euthanized because of acute atraumatic, flaccid paralysis of the hind limbs.  At necropsy, lesions were present from the 3rd through the 7th lumbar spinal cord segments and the 1st through the 3rd sacral segments.

 

HISTOPATHOLOGIC DESCRIPTION:  Spinal cord, lumbar:  Within the ventral horns and ventral funiculi, most severely affecting the gray matter, there are multifocal, up to 2x1mm, asymmetrical areas of necrosis characterized by cavitation and loss of normal neurofibrillary architecture (infarcts)  with replacement by debris, mild hemorrhage and numerous foamy macrophages (gitter cells).  Multifocally, vessels within the adjacent gray and white matter and meninges are variably occluded by pale, amphophilic, fibrocartilaginous emboli.  Adjacent to necrotic areas there are increased numbers of elongate microglial cells (rod cells), occasional degenerate neurons characterized by swollen neuronal cell bodies with pale central cytoplasm with dispersed Nissl substance and peripheralized nucleus (central chromatolysis), and scattered spongiosis.  Multifocally within the ventral funiculus there are areas of axonal degeneration (Wallerian degeneration) characterized by dilated myelin sheaths with swollen, homogeneous eosinophilic axons (spheroids) or with loss of axons and replacement by necrotic debris or gitter cells (ellipsoids).  There is a focally extensive area of dural ossification up to 0.5 mm in diameter.

 

MORPHOLOGICAL DIAGNOSES:

1.  Spinal cord, lumbar, grey and white matter:  Necrosis, multifocal and asymmetrical, with multiple fibrocartilaginous emboli (infarcts) and Wallerian degeneration, great Dane, canine.

2.  Spinal cord, lumbar, dura mater:  Dural ossification, focal.

 

ETIOLOGIC DIAGNOSIS:  Embolic myelopathy (Ischemic myelopathy due to fibrocartilaginous embolism)

 

GENERAL DISCUSSION

·       Fibrocartilaginous embolic myelopathy (FCME) is a peracute neurological syndrome in which fibrocartilaginous emboli cause ischemic necrosis and infarcts in the spinal cord 

·       Emboli usually occlude leptomeningeal or intramedullary vessels

·       All levels of the spinal cord can be affected

·       Primarily affects large and giant breed dogs between the ages of 3 to 7 years

·       Common in dogs and occurs less frequently in other domestic animals

·       Not reported in chondrodystrophic breeds

·       Miniature Schnauzers are the most commonly affected small breed

 

PATHOGENESIS

·       Pathogenesis is not clearly delineated

·       Generally associated with type II herniations

·       Recent history of exercise is common

·       One study reported that 60% of confirmed cases of canine ischemic myelopathy had a history of trauma or exercise

·       Histochemicalliy identical to the nucleus pulposus of an intervertebral disk

·       Theories on the entry of the nucleus pulposus into the vascular system:


·       Herniation of the nucleus pulposus directly into the longitudinal internal ventral vertebral venous plexus with reflux back to the spinal cord vasculature            

·       Presence of arteriovenous connections

·       Entrance of nucleus pulposus through reactive, newly formed arterial vessels in the annulus fibrosus and from small arteries in the disk

·       Prolapse of nucleus pulposus into marrow cavity of adjacent vertebral body

 

TYPICAL CLINICAL FINDINGS:

·       Affected dogs are bright and alert

·       Rapid progression from apparent lameness to paralysis in one or more limbs over the course of a few hours followed by static clinical signs

·       Paralysis is frequently asymmetrical

·       60% of canine cases present with pelvic limb deficits

·       A combination of lower and upper motor neuron pareses is commonly seen

·       Pain is often diminished

·       Hyperesthesia is absent

·       Ipsilateral Horner’s syndrome may be present if there is severe injury to the cervical lateral funiculus or the gray matter of the cranial thoracic segments

·       Spinal radiographs often appear normal

·       Cerebral spinal fluid (CSF) may have elevated protein concentration with normal cell count (albuminocytologic dissociation)

·       The white blood cell count in the CSF may occasionally be slightly elevated during the early stages as a result of the inflammatory reaction to the spinal cord ischemia

 

TYPICAL GROSS FINDINGS:

·       Acute focal infarct involving cervical or lumbar cord most commonly 

·       Affected segments may appear slightly swollen and soft (malacia)

·       Cord surface may be gray (total ischemia) or red/brown (hemorrhage)

·       Elevation/rupture of the annulus fibrosus and dorsal longitudinal ligament with extrusion of nucleus pulposus may be noted

·       The disc may be macroscopically normal

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

·       The diagnostic finding is the intravascular emboli of fibrocartilage that may completely or partially occlude the affected blood vessel

·       Commonly the ventral spinal artery and vein

·       Necrosis can be localized or diffuse

·       Gray matter necrosis: Embolus size dependent and occlusion of the spinal artery or its central (sulcal) branches

·       White matter necrosis: Occlusion of circumferential branches (arterial vasocorona)  of the spinal and radicular arteries

·       Margins of lesion are well demarcated

·       Neuronal and glial ghosts are common

·       Chronic lesions have neovascularization at periphery with macrophage aggregates and few neutrophils

·       Ischemic areas liquefy and have abundant gitter cells

·       Wallerian degeneration may develop if ventral gray matter horns are affected

·       Emboli may be seen in leptomeningeal and intramedullary vessels

 

ADDITIONAL DIAGNOSTIC TESTS:

·       Myelogram to determine spinal cord swelling

·       Emboli stain blue-gray with H&E,  tan with phosphotungstic acid hematoxylin (PTAH), blue with Alcian blue, and are PAS positive

·       Striking metachromasia of the material with toluidine blue is helpful in locating the emboli

 

DIFFERENTIAL DIAGNOSIS:

·       Rapid paresis/paralysis

·       Intervertebral disc disease

·       Trauma to vertebrae/spinal cord

 

COMPARATIVE PATHOLOGY

·       Also reported in the cat, horse, pig, sheep, and man

·       In man –  associated with trauma

·       Schmorl’s node – protrusion of the cartilage of the intervertebral disc through the vertebral body endplate and into the adjacent vertebra

·       Mink – emboli possibly in the pulmonary arteries

·       Schmorl’s nodes are common

 

References:

1.        Adaska JA, Lynch S. Fibrocartilaginous embolic myelopathy in a Sumatran tiger (Panthera tigris sumatrae). J Zoo Wildl Med. 2004;35:242-244.

2.        Hawthorne JC, Wallace LJ, Fenner WR, Waters DJ. Fibrocartilagenous embolic myelopathy in miniature schnauzers. J Am Anim Hosp Assoc. 2001;37:374-383.

3.        Landolfi JA, Saunders GK, Swecker WS. Fibrocartilaginousembolic myelopathy in a calf. J Vet Diagn Invest. 2004;16:360-362.

4.        Oliver JE, Lorenz MD, Kornegay JN. Pelvic limb paresis, paralysis, or ataxia. In: Oliver JE, Lorenz MD, Kornegay JN eds. Handbook of Veterinary Neurology, 3rd ed. Philadelphia, PA: W.B. Saunders Co.; 1997:157-158.

5.        Ricci E, Cavicchio P, Cantile C. Fibrocartilaginous embolic myelopathy in a lion (Panthera leo). J Zoo Wildl Med. 2010;41(2):334-7.

6.        Stedman NL, Brown TP, Rowland GN. Intravascular cartilaginous emboli in the spinal cord of turkeys. Av Dis. 1998;42:423-428.

7.        Summers BA, Cummings JF, de Lahunta A. Degenerative diseases of the central nervous system.  In: Duncan L, ed. Veterinary Neuropathology. St. Louis, MO: Mosby; 1995:246-249.

8.        Thompson K. Bones and joints. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 5th ed. Philadelphia, PA: Elsevier; 2007:156-157.

9.        Vadevelde M, Higgins RJ, Oevermann A.  Vascular disorders. In: Vadevelde M, Higgins RJ, Oevermann A, eds. Veterinary Neuropathology: Essentials of Theory and Practice. 1st ed. Ames, IA: Wiley-Blackwell: 2012:44-56.

10.     Walling BE, Stewart MC, Valli VE. Pathology in practice. Fibrocartilaginous embolism. J Am Vet Med Assoc. 2011;239(2):199-201.

 

 


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