Page 1169 - Small Animal Internal Medicine, 6th Edition

CHAPTER 65 Disorders of the Spinal Cord 1141

thoracolumbar IVD extrusion presenting with complete FIBROCARTILAGINOUS EMBOLISM
paralysis and loss of deep pain perception, focal spinal cord Acute infarction and ischemic necrosis of the spinal cord
VetBooks.ir damage and swelling result in spinal cord ischemia and pro- parenchyma occur when fibrocartilage presumably from the
nucleus pulposus of the IVD is embolized into the very small
gressive myelomalacia of the cord cranial and caudal to the
original lesion (i.e., ascending descending myelomalacia, pro-
leptomeninges. This causes peracute nonprogressive signs of
gressive hemorrhagic malacia). This condition usually devel- arteries and veins supplying the spinal cord parenchyma and
ops within 5 days of the original disk extrusion. Myelomalacia spinal cord dysfunction affecting any region of the spinal
should be suspected when the line demarcating the presence cord and results in paresis or paralysis. The cause of this
of the cutaneous trunci reflex moves cranially or the patellar disorder is unknown. It is most common in medium-sized
and withdrawal reflexes are lost (LMN signs) in the rear and large-breed dogs. It has also been described in small-
limbs of a dog that had UMN paralysis in the rear limbs breed dogs, especially the Miniature Schnauzer, and in a few
when first evaluated. Most affected dogs are also very anxious cats. Most affected dogs are young or middle-aged, with the
and experience a great deal of pain. When ascending majority of cases between 3 and 7 years of age. A few dogs
descending myelomalacia is recognized, euthanasia should younger than 1 year of age have been recognized with FCE,
be recommended; no chance for recovery exists, and most especially Irish Wolfhounds. No gender predilection exists.
affected dogs will die within a few days of respiratory
paralysis. Clinical Features
The onset of neurologic signs is very sudden. In about half
TRAUMATIC DISK EXTRUSIONS of all cases, FCE occurs immediately after minor trauma
Exercise or trauma-induced peracute disk extrusions (Han- or during exertion. Neurologic examination reflects a focal
sen’s type III disk extrusion, acute noncompressive nucleus spinal cord lesion, and the deficits observed depend on the
pulposus extrusion: ANNPE) occur occasionally in dogs region of spinal cord affected and severity of cord involve-
without preexisting degenerative disk disease. The sudden ment. The thoracolumbar cord (causing UMN signs in the
explosive rupture of the annulus in these dogs usually occurs rear limbs) and the lumbosacral intumescence (causing
during running or jumping or in association with a fall or LMN signs in the rear limbs) are most often affected. The
motor vehicle accident. This results in an acute nucleus pul- cervical cord is affected less frequently (10%), but it may
posus extrusion with neurologic signs caused by spinal cord be the site most often affected in small-breed dogs. Neu-
bruising, hemorrhage, and edema. Predisposed breeds rologic dysfunction may be mild or severe. Asymmetry is
include Border Collies, Labrador Retrievers, Staffordshire common, with the right and left sides affected to different
Bull Terriers, Sighthounds, and other large-breed athletic degrees. Dogs may cry out as though in pain at the onset
dogs. The onset of signs is peracute and associated initially of signs, and dogs evaluated within 2 to 6 hours of onset
with discomfort, but within 12 to 24 hours there is no site of sometimes exhibit focal spinal hyperpathia (i.e., painful-
pain on spinal palpation. Neurologic signs reflect the loca- ness); however, this resolves quickly, and most affected dogs
tion and severity of the spinal injury. Asymmetry is common. do not exhibit pain by the time they are brought to a veteri-
Spinal radiographs do not reveal evidence of chronic disk narian, even on manipulation of their spine. The lack of pain
degeneration or mineralization, but mild IVD space narrow- and the asymmetry are very helpful in differentiating FCE
ing is often evident at the site of disk extrusion. Advanced from other disorders that cause peracute nonprogressive
imaging typically reveals a focal area of T2 weighted (T2W) neurologic dysfunction, such as acute type I IVD extrusion
intramedullary spinal cord hyperintensity overlying an IVD and fracture/luxation. FCE typically causes peracute non-
space, a reduced volume of the T2W hyperintense nucleus progressive signs, but up to 30% of affected dogs can have
pulposus signal at that site, mild narrowing of the associated some worsening of neurologic signs within minutes to hours
disk space, and a variable amount of extradural material in of onset.
the canal at that site with little or no spinal cord compression.
The pathology in these dogs is related to cord bruising and Diagnosis
hemorrhage from the force of the disk extrusion without FCE is suspected on the basis of signalment, history, and
significant spinal cord compression, so surgical decompres- recognition of peracute, nonprogressive, nonpainful spinal
sion is not warranted. Traumatic disk extrusion in older dogs cord dysfunction. Spinal radiographs are normal but assist
and chondrodystrophic dogs will occasionally (<30%) result in ruling out diskospondylitis, fractures, lytic vertebral neo-
in moderate to severe spinal cord compression by extruded plasia, and IVDD. CSF is usually normal, although an
disk material requiring surgical decompression so imaging increase in protein (especially albumin) concentration may
should always be recommended. The recommended treat- be observed in some (50%) cases, and neutrophil numbers
ment for noncompressive traumatic disk extrusion is sup- may be slightly increased within the CSF in the first 24 hours
portive care and physical therapy. Most dogs that have deep after the onset of clinical signs. Myelography or spinal CT
pain sensation will regain the ability to walk within 1 to 4 may be performed to rule out compressive lesions of the
weeks, but some residual paresis is common. Urinary or fecal spinal cord for which emergency surgery might be indicated,
incontinence, when present, may take longer to recover from such as fractures, disk extrusion, and neoplasia. MRI may
or may be permanent. reveal focal edema and T2W hyperintensity within the spinal