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16

Neurological Disease of the Thoracic Limb

Lisa Bartner

Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA

16.1 Introduction

When presented with a patient displaying a thoracic limb lameness, neurologic dysfunction should
always be considered a differential diagnosis and a systematic approach is necessary to determine the
cause of the gait abnormality. While there are many conditions affecting both thoracic limbs, these
conditions are generally less confusing to differentiate from orthopedic disease than a dog presenting
with monoparesis or unilateral neurogenic lameness (see Chapter 4 for definitions, Box 4.1).
Furthermore, as described in Chapter 4, the same condition may result in monoparesis and/or uni-
lateral neurogenic lameness if the dorsal and ventral nerve roots are affected, because of the close
juxtaposition between sensory and motor components supplied by these two. For example, a nerve
sheath tumor affecting the nerve root may cause inability to support weight (ventral root involve-
ment) and pain during weight support (dorsal root involvement). The focus of this chapter is diseases
that cause symptoms that can easily be confused with orthopedic causes of lameness (in its broader
applied terminology). For nervous system conditions, an anatomic diagnosis must be reached before
making a list of etiologic diagnoses; Chapter 4 described the neurologic examination and localization
(i.e. anatomic diagnosis). Table 16.1 outlines common differential diagnoses and diagnostic steps for
neurological diseases causing monoparesis or neurogenic lameness of the thoracic limb.

Video 16.1

Complete brachial plexus avulsion: clinical exam and presentation.

16.2 Relevant Anatomy

Branches of the sixth, seventh, eighth cervical, and the first and second thoracic spinal nerves fuse
and form the brachial plexus. There is variability among individual animals where some can either
have the fifth cervical and/or or lack the second thoracic spinal nerve(s), sometimes referred to as

Canine Lameness, First Edition. Edited by Felix Michael Duerr.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/duerr/lameness