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17

Neoplastic Conditions of the Thoracic Limb

Bernard Séguin

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

17.1 Introduction

One of the most important neoplastic differential diagnoses for thoracic limb lameness includes
osteosarcoma of the distal radius and proximal humerus. However, other neoplastic conditions,
such as brachial plexus tumors and soft tissue tumors affecting the triceps, should also be consid-
ered. Although these latter tumors are rare, establishing a diagnosis early during the course of
progression is crucial to provide the best treatment and outcome possible. Please refer to Chapter 11
for details regarding the diagnostic workup of neoplasia.

17.2 Neoplasia of Specific Regions

17.2.1 Distal Limb Region
Tumors of the distal region of the limb commonly lead to visible swelling and/or palpable mass
formation, thereby making them visible to owners. On the other hand, absence of swelling or a
mass does not rule out neoplasia. Dogs may also present with lameness. Pain on palpation is a com-
mon finding but because some dogs do not tolerate palpation of their digits or manus/pes, inter-
pretation of the physical exam findings in these dogs can sometimes be difficult. Radiographs
should be considered whenever any subcutaneous tumors or non‐movable masses or swellings are
identified. Digital lesions causing bone lysis are more likely to be a malignant neoplasm (Marino
et al. 1995); however, common differential diagnoses include osteoarthritis and osteomyelitis. To
obtain a diagnosis, a fine‐needle aspirate (FNA) can be performed for non‐osseous tumors or osse-
ous tumors with lysis. A biopsy is generally necessary for non‐lytic osseous tumors or when a
nondiagnostic sample is acquired from FNA. Once a diagnosis of neoplasia is suspected or con-
firmed, chest radiographs and FNA of the regional lymph node(s) should be considered.
Neoplasia of the distal limb can be arbitrarily divided into tumors that affect the digits and those
that affect other tissues (i.e. non‐digital tumors). Regarding the latter, the most common non‐digital
tumors include mast cell tumor and soft tissue sarcoma, and the diagnostic approach to these

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