Page 852 - Clinical Small Animal Internal Medicine

820 Section 8 Neurologic Disease

Cerebrospinal fluid (CSF) is contained within the sub- cord disorders by cross‐sectional imaging and CSF
VetBooks.ir arachnoid space, which lies between the arachnoid and analysis combined with results for the SOD1 mutation
analysis. A dog with progressive T3–L3 myelopathy that
pia mater. Cerebrospinal fluid analysis will assist with
determining the presence of inflammatory disease.
the SOD1 mutation is likely to have degenerative
Abnormalities in CSF cytology and protein are sensitive has normal neurodiagnostics and is homozygous for
indicators of CNS disease but rarely specific for a disease myelopathy.
process. On occasion, infectious organisms or neoplastic Degenerative conditions of the vertebral column such
cells may be identified. The CSF profile, including protein as intervertebral disc herniation, cervical spondylomye-
content, cell counts and cytology, will assist the clinician lopathy, and degenerative lumbosacral stenosis second-
to narrow the differential diagnosis. arily cause myelopathy by spinal cord compression.
Additional diagnostic procedures include electrodiag- Other less common degenerative conditions of the
nostic evaluation (electromyography and nerve conduc- vertebral column include synovial cysts, canal stenosis,
tion studies), CSF protein electrophoresis, serology, and and diffuse idiopathic skeletal hyperostosis (DISH).
exploratory surgery.
Anomalies
Differential Diagnosis Dogs and cats with congenital spinal malformations
often have abnormalities involving multiple segments of
Myelopathies can be classified according to the DAMNIT the vertebral column and spinal cord. Malformations
V scheme (degenerative, anomalous, metabolic, neoplas- associated with the spinal cord are often referred to as
tic, nutritional, inflammatory‐infectious/noninfectious, spinal dysraphism that involve defects in closure of the
traumatic, toxic, vascular) (see Tables 76.1 and 76.2). neural tube. Such defects may also involve the vertebral
column. Spinal dysraphism is a result of abnormal mid-
line fusion and disrupts the normal pattern of spinal cord
Degenerative
circuits. Other defects include syringomyelia, dermoid
Degenerative conditions of the spinal cord can occur in sinus, spina bifida, and caudal vertebral hypoplasia.
both young and adult animals. Myelinopathies, axonopa- Genetic mutations and exposure to toxic and infectious
thies, and neuronopathies present initially with progres- agents at certain stages of development can lead to these
sive signs of paraparesis and eventual tetraparesis. Many malformations. Abnormal formation of vertebral bodies
of these conditions are breed specific and inherited. by itself does not cause spinal cord dysfunction but some
Recent identification of gene mutations has enhanced conditions can cause myelopathy from spinal cord com-
our understanding of the underlying pathogenesis for pression or spinal canal stenosis.
many degenerative conditions associated with ion chan- Congenital anomalies affecting the craniocervical
nel defects, abnormalities in protein aggregation, loss of junction include atlantoaxial instability and atlantooc-
enzyme function (storage disease), and dysfunction in cipital overlapping, which also can occur simultaneously.
protein metabolism and growth factors. The subsequent spinal cord compression results in signs
Canine degenerative myelopathy (DM) is an adult‐ of C1–5 myelopathy or manifests as cervical spinal pain.
onset neurodegenerative disease. Most dogs are at least 8
years old before onset of clinical signs. The initial signs Metabolic
of degenerative myelopathy typically include asymmetric
GP ataxia and spastic paresis in the pelvic limbs. At this Endocrocrine‐related peripheral neuropathies such as
stage, segmental spinal reflexes are indicative of UMN diabetes mellitus, hypothyroidism, and insulinoma para-
loss. Dogs become nonambulatory paraparetic within neoplastic neuropathy reflect as sciatic nerve disease.
one year after onset. When euthanasia is delayed, weak- Clinical signs appear in the pelvic limbs first and may
ness can ascend to the thoracic limbs with emergence of mimic myelopathy.
LMN signs, dysphagia, and widespread muscle atrophy.
Recently, a missense mutation in the gene superoxide Neoplastic
dismutase 1 (SOD1) was established as a genetic “risk
factor” for dogs developing DM. Dogs that are homozy- Tumors affecting the spinal cord are described as extra-
gous (two copies of the mutant allele) for the SOD1 dural, intradural‐extramedullary, and intramedullary
mutation are considered at risk for developing degenera- based on location with respect to the spinal cord.
tive myelopathy. Because a variety of common acquired Intramedullary tumors include gliomas (astrocytoma,
compressive spinal cord diseases can mimic early DM, a oligodendroglioma, and ependymoma) and neuronal‐
presumptive diagnosis is made by ruling out other spinal derived tumors. Common intradural‐extramedullary