Page 294 - Canine Lameness

266 16 ­Neurorogico giNciN rAectNe trucigi gim

16.3.3 Myopathies and Junctionopathies
Myopathies include disorders of skeletal and smooth muscle that can be acquired, hereditary, and
congenital (Taylor 2000). More commonly encountered conditions causing shifting lameness
include polymyositis, endocrine myopathies, and infectious myopathies. Fibrotic myopathies such
as infraspinatus contracture may also cause a unilateral lameness; this condition is commonly
confused with neurologic origin (Chapter 15).
Junctionopathies refer to conditions altering the neuromuscular junction, with myasthenia gravis
being the most reported and investigated. These are typified by generalized paresis, fatiguability,
and stiff and stilted gait. Occasionally a shifting or unilateral leg lameness, particularly during the
early stages, is reported but more commonly affects the pelvic limbs first (Chapter 21).
Diagnosis of myopathies and junctionopathies is supported by clinical presentation and exami-
nation and, in many cases, is confirmed by muscle and/or nerve biopsies. Serum muscle enzyme
levels (creatine kinase, lactate dehydrogenase, and aspartate aminotransferase) are elevated in
myositis while elevated titers of acetylcholine receptor antibodies confirm a diagnosis of myasthe-
nia gravis (Chapter 21). Treatment and prognosis are highly variable and will depend on the spe-
cific condition present.

16.3.4 Other Spinal Diseases Affecting the Thoracic Limb
While not a neurologic condition, dogs with immune-mediated polyarthritis (IMPA) can first pre-
sent with spinal hyperesthesia (Shaughnessy et al. 2016). Since affected animals may not show
accompanying peripheral joint effusion or pain upon range of motion (Chapter 13), this disease
can be confused with a neurologic problem. A shifting leg lameness and short-stilted gait may also
first appear in a single limb prior to becoming more generalized. The neurologic exam is usually
normal. Joint fluid analysis is necessary to establish a diagnosis (Chapter 9). Additionally, IMPA
can occur concurrently with SRMA in some dogs, another cause of cervical spinal pain.
The following conditions rarely cause neurologic deficits and clinical signs unless nerve roots
are involved, in which case a lameness or monoparesis may be seen:
Spondylosis deformans is a noninflammatory, degenerative disease of the vertebral column thought
to be caused by degeneration of the annulus fibrosis and its bony attachments (Romatowski
1986). Typical radiographic features include focal new bone formation and osteophytes on the
ventral and lateral aspects of the vertebrae (Figure 21.1F). Spondylosis deformans is a frequently
encountered condition and while it may be associated with IVD protrusions and foraminal ste-
nosis, almost always, it is an incidental finding. As such, a radiographic diagnosis of this condi-
tion should not be overinterpreted as a clinical problem. Importantly, while the term spondylosis
sounds similar to spondylitis (i.e. discospondylitis), these two conditions are entirely different
and must be differentiated. Most readily, the vertebral end plates in spondylosis are radiographi-
cally smooth and regular in contrast to the lytic and irregular end plates of discospondylitis
(Chapter 21).
Diffuse idiopathic skeletal hyperostosis (DISH) is a rare condition that affects the axial and appen-
dicular skeleton of young dogs. It causes extensive ossification of soft tissues along the vertebral
bodies, including the spinal ventral longitudinal ligament (Figure 16.1D). There is resulting
bridging of the disc spaces without evidence of IVD degeneration (Kranenburg et al. 2011).
DISH is rarely associated with clinical signs, but nerve root entrapment from foraminal stenosis
has been described (Taylor-Brown and De Decker 2017).