Front Matter

Chapter 17 Diagnosis of and Treatment Options for Disorders of the Spine 445

atrophy in muscle, nerve fiber loss with axonal
degeneration, and secondary myelin loss in
myelinated fibers of the peripheral nerves
(Awano et al., 2009; Shelton et al., 2012). Studies
conducted on the thoracic intercostal muscles
and associated thoracic motor and sensory neu­
rons of dogs with DM indicate that there are
significant atrophic changes in these muscles at
defined disease stages but there is no apparent
degeneration of the associated motor neurons
(Morgan et al., 2013, 2014). However, significant
sensory neuron degeneration did precede any
evidence of motor neuron pathology (Morgan
et al., 2014). The clinical spectrum of DM has
now been broadened to involve both the UMN
and LMN systems and is considered a multi­
system disease involving the central and
peripheral motor and sensory axons (Coates &
Wininger, 2010; Johnston et al., 2001).

Since most of the dogs in the initial reports

were German Shepherd Dogs, the disease also

was called German Shepherd Dog myelopathy

(Braund & Vandevelde, 1978). However, in those

same earlier reports, other breeds were repre­

sented (Averill, 1973; Braund & Vandevelde,

1978). Canine DM is now recognized as a com­

mon problem in a number of pure breeds and

mixed breeds with an overall prevalence of

0.19% (Coates et al., 2007; Zeng et al., 2014).

Pathophysiology

The cause underlying canine DM has been

enigmatic for many years. In 2009, Awano and

collegues identified a c.118G >A transition in the

SOD1 gene that predicted an E40K missense

underlying canine DM. In this initial study, there

Table 17.1 Classification of myelin, axonal, and neuronal disorders of the central nervous system (CNS) (spinal cord)
and peripheral nervous system (PNS)

Neuroanatomic pathology Specific description

CNS—Encephalopathy/encephalomyelopathy

Myelinopathy Hypomyelination

Dysmyelination: leukodystrophy, myelinolytic disorders

Leukomyelopathy

Leukoencephalomyelopathy

Spongy degeneration Myelin vacuolation

Neuronal vacuolation

Axonopathy: Wallerian degeneration, distal

axonopathy (dying‐back neuropathy), segmental

degeneration

Central axonopathy

Central–peripheral axonopathy

Central–peripheral distal axonopathy

Neuroaxonal dystrophy Axonal transport disorder

Multisystem degeneration Axonopathy, neuronopathy, and neuropathy

PNS—Neuropathy

Neuronopathy: degeneration and loss of neurons,

neurofibrillary accumulations in neurons

Motor neuronopathy

Sensory neuronopathy

Myelinopathy Segmental demyelination

Hypomyelination

Axonopathy Sensory–motor neuropathy: distal sensorimotor,

central–peripheral distal axonopathy

Sensory neuropathy

Metabolic neuropathy

Autonomic neuropathy