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242 Degenerative Myelopathy

PHYSICAL EXAM FINDINGS • Degenerative lumbosacral stenosis TREATMENT
Early disease: upper motor neuron (UMN) • Cervical spondylomyelopathy Treatment Overview
VetBooks.ir • Asymmetrical truncal general proprioceptive Initial Database There are no proven effective therapies for DM.
• Other coexisting orthopedic diseases and
signs in pelvic limbs:
spinal cord disorders
Supportive and palliative care are provided to
ataxia
• UMN spastic paraparesis (long stride length)
• Postural reaction deficits (e.g., toe dragging, • Neurologic exam (p. 1136) maintain quality of life.
absent proprioceptive placement [paw ○ See Physical Exam Findings above for Acute and Chronic Treatment
replacement]) clinical findings. Exercise, vitamin supplementation (B 12 , E, and
• Spinal reflexes present or exaggerated ■ Nonpainful progressive myelopathy C), and protease inhibitors (aminocaproic acid)
• Absence of paraspinal hyperesthesia ○ Neuroanatomic localization: initial disease have been advocated as potential therapies,
Late disease: lower motor neuron (LMN) signs stage—UMN signs (T3 to L3 spinal cord although efficacy of medical therapy still
and spread to thoracic limbs: segments); later disease stage involves remains to be proven.
• Paraplegia and LMN signs develop in pelvic LMN signs to the pelvic and thoracic • Ongoing clinical trials are testing therapeutic
limbs; then weakness and neurogenic muscle limbs; terminal stage—generalized LMN strategies for canine DM.
atrophy spread to thoracic limbs. signs to include brainstem signs • Encourage exercise and physical rehabilitation
• Widespread muscle atrophy and wasting • Clinical pathologic tests: generally unremarkable in ambulatory dogs to slow onset of disuse
• Flaccid tetraparesis • Thoracic radiography muscle atrophy.
• Urinary and fecal incontinence ○ Screening for metastatic neoplasia (CNS • When the dog becomes nonambulatory, keep
• End stage: swallowing and respiratory neoplasia, differential diagnosis) on a well-padded surface.
dysfunction • Survey spinal radiography • Monitor for urinary and fecal incontinence.
• Genetic testing ○ Basic nursing care and hygiene if inconti-
Etiology and Pathophysiology ○ A direct mutation test for a suscep- nence occurs to prevent the onset of urine
Cause: mutation in the SOD1 gene, resulting tibility gene is available through the scald, infected decubital ulcers, or similar
in a toxic gain of function Orthopedic Foundation for Animals skin lesions
• Misfolding of the SOD protein causes (www.offa.org) and other genetic testing • Monitor for decubital ulcers in dogs with
abnormal accumulations of aggregates in companies. For diagnostic purposes, a generalized muscle atrophy.
the neuron. blood sample can be submitted through • Assistive walking devices enable ambulation
• Dogs homozygous for the mutation are at the Animal Molecular Genetic Diseases support and improve quality of life.
risk for DM. Laboratory at the University of Missouri
• Neuropathologic lesion distribution in (www.caninegeneticdiseases.net). Possible Complications
the CNS involves axons and myelin in all ○ Dogs that are homozygous for the muta- • Urinary tract infection; see bacterial cystitis
funiculi of the spinal cord, notably the dorsal tion are at risk for DM, but not all at-risk (p. 232)
funiculus and dorsal portion of the lateral dogs will develop DM. Some dogs that • Decubital ulcer formation
funiculus of the thoracolumbar spinal cord. are heterozygous for the mutation have
• Neurons in affected dogs contain cytoplas- developed DM. Recommended Monitoring
mic aggregates that stain with anti-SOD1 ○ For recessive diseases, the results are • Monitor for secondary urinary tract infection.
antibodies and show loss in terminal disease. expressed as follows: • Monitor for proper nursing care.
• Some studies have shown degenerative ■ Normal: homozygous for the normal
changes in some neurons of the brainstem. gene PROGNOSIS & OUTCOME
• Dogs with chronic DM develop muscle ■ Carrier: heterozygous, with one copy
atrophy consistent with denervation. each of the normal and mutated gene • Long-term prognosis is considered poor.
Peripheral nerve lesions are consistent with ■ At risk: homozygous for the mutated • Dogs often lose their ability to ambulate
an axonopathy and secondary demyelination. gene in the pelvic limbs within 12 months from
• The clinical spectrum of DM has now been onset of signs.
broadened to include the UMN and LMN Advanced or Confirmatory Testing • The disease eventually will progress to
systems and is considered a multisystem • Clinical working diagnosis is based on ruling affect the thoracic limbs and swallowing
disease involving central and peripheral out other diseases that cause progressive function.
axons. myelopathy. • Owners of large dogs often will elect for
• Cerebrospinal fluid analysis (pp. 1080 euthanasia when their dog needs ambulatory
DIAGNOSIS and 1323): may show increased protein assistance.
concentration.
Diagnostic Overview • Electrophysiologic testing PEARLS & CONSIDERATIONS
The diagnosis of DM is based on exclusion of ○ Electromyography and nerve conduction
other spinal cord disorders that mimic it. The studies Comments
genetic test may assist with interpretation of ○ Used for ruling out other neuropathic • Lack of paraspinal hyperesthesia is a key
clinical signs and diagnostic testing toward a disorders clinical feature of DM.
presumptive diagnosis of DM. ○ In later disease stage, dogs with DM show • A suspected diagnosis is based on exclusion
evidence of peripheral axonopathy and of other spinal cord disorders.
Differential Diagnosis secondary demyelination.
Other spinal cord disorders mimic signs of DM: • Cross-sectional imaging: no evidence of a Technician Tips
• Intervertebral disc disease: Hansen type II compressive myelopathy • Physical rehabilitation using light exercise
○ The Pembroke Welsh corgi is a chon- ○ CT combined with myelography may improve the patient’s quality of life.
drodystrophic breed that is also prone ○ MRI (p. 1132) • Caution must be used when rehabilitation—
to Hansen type I intervertebral disc disease • Definitive diagnosis is determined only by especially therapeutic exercise—is considered
• Inflammatory disease of the spinal cord: postmortem histopathologic examination because these dogs can be exhausted easily.
myelitis of the spinal cord and peripheral nervous Inducing fatigue in already diseased muscle
• Spinal cord neoplasia system. can potentially hasten the disease process.

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