Page 70 - Canine Lameness

42 4 The Neurologic Examination

Box 4.1 Neurologic Components of Gait Abnormalities
Neurogenic lameness (= Nerve root signature lameness)
●
○ UMN lesion
Not commonly associated with neurogenic lameness
■
○ LMN lesion
= Pathology affecting the afferent (dorsal) nerve root or meninges (=pain)
■
Paresis (= Partial loss of voluntary movement)
●
○ UMN lesion (brain, spinal cord: C1–C5, T3–L3)
■ = Disruption of signal transmission from brain to LMN resulting in inability to initiate
gait voluntarily (= spastic paresis)
= Pathology affecting brain or spinal cord
■
○ LMN lesion (spinal cord: C6–T2, L4–S3; nerves, neuromuscular junction, and muscle)
■ = Disruption of signal transmission from LMN to muscle resulting in inability to sup-
port weight (= flaccid paresis)
= Pathology affecting spinal cord, efferent (ventral) nerve roots, muscles, or neuromus-
■
cular junction
● Ataxia (= Incoordination)
○ UMN lesion
= General proprioceptive (brainstem, spinal cord: C1–5, T3–L3)
■
= Vestibular
■
■ = Cerebellar
○ LMN lesion
Not associated with ataxia
■

cause weakness (e.g. profound anemia, electrolyte disturbances, and nutritional deficits); in this
text, paresis will be used when referring to primary neurologic causes.
Ataxia is characterized by uncoordinated movement and originates from within the central
nervous system (CNS). Since it generally affects multiple limbs, it is not commonly confused with
orthopedic causes of lameness.
Animals with neurologic disease may display a combination of neurogenic lameness, paresis,
and/or ataxia. For example, a disc compressing the nerve roots can result in both monoparesis and
neurogenic lameness, which can be explained by involvement of ventral and dorsal nerve roots
(due to their close anatomic proximity), respectively. If the disc herniation is also compressing the
spinal cord white matter, ataxia will be evident caudal to the lesion.

4.2 Neuroanatomy Related to Limb Function

4.2.1 Anatomical Components of the Nervous System
There are three main components of the nervous system: the CNS, peripheral nervous system
(PNS), and autonomic nervous system (ANS). The CNS consists of the brain and spinal cord. The
cell bodies of the neurons are located throughout and synapse on LMNs of the PNS or ANS. The
ANS unconsciously regulates important body functions including the respiratory and circulatory
system and as such is not relevant to lameness. Most causes of lameness or paresis related to the