Page 166 - Canine Lameness

138 11 Diagnostic Approach to Neoplastic Conditions Causing Lameness

11.3 Specific Tumors

Many histologic types of neoplasm cause lameness in dogs. Both skin and subcutaneous tumors
may occur in the thoracic and pelvic limbs. Tumors can also originate from muscles, bones, or the
joint capsule.

11.3.1 Skin and Subcutaneous Neoplasia
Tumors of the skin and subcutaneous tissues can affect any aspect of the limbs. Common tumors
of the skin and subcutaneous tissues are mast cell tumors, soft tissue sarcomas, and lipomas. Both
skin and subcutaneous tumors can cause lameness if they are painful. Furthermore, subcutaneous
tumors can interfere with the tendons, muscles, and joint motion or irritate adjacent nerves and
thereby result in lameness. Infiltrative tumors into a muscle, such as infiltrative lipoma or soft tis-
sue sarcoma, are examples of a tumor that can interfere with muscle function.

11.3.2 Muscle Neoplasia

Tumors of the muscles are not well described in the canine literature, and primary tumors of the
muscles, such as rhabdomyosarcomas, appear to be quite rare. Anecdotally, other tumors arising
within a muscle, such as hemangiosarcoma, histiocytic sarcoma, and soft tissue sarcoma, are more
common than primary muscle tumors. Other differentials for mass effects in muscles include
infection and muscle tears. Tumors of the muscle should be considered as a differential diagnosis,
particularly if swelling and muscle tears are observed without a history of trauma.

11.3.3 Bone Neoplasia

Tumors of the bones and synovium frequently cause severe lameness because of their intimate
association with the tissues involved in motion. Tumors of the bone can be either primary or meta-
static. Primary bone tumors can be osteosarcoma, chondrosarcoma, fibrosarcoma, and hemangio-
sarcoma. By far the most common (98% in one study) tumor of the appendicular skeleton is
osteosarcoma with large and giant breeds being predisposed. Osteosarcoma is most commonly
diagnosed in 7–9 year old dogs, however, even dogs of 1–2 years of age may be affected (Liptak et al.
2004). Osteosarcoma most commonly occurs in the metaphyseal regions of bones, most frequently
in the distal radius and proximal humerus. Diaphyseal lesions have been reported but are uncom-
mon. Chondrosarcoma is the second most common bone tumor.
As a rule, any carcinoma of a bone should be considered metastatic. As such, once a bone carci-
noma is diagnosed, the primary tumor should be identified. In general, a thorough physical exam
(including a rectal exam), radiographs of the chest and abdomen, and abdominal ultrasound are
appropriate first steps.
Other tumors affecting the bones include lymphoma and plasma cell tumor/multiple myeloma.
Multiple myeloma can be associated with hyperglobulinemia. A chemistry panel and protein elec-
trophoresis may be used to detect a monoclonal gammopathy.

11.3.4 Joint Capsule Neoplasia
The most common tumors arising from the joint capsule are histiocytic sarcoma, synovial myxo-
mas, and synovial cell sarcoma (Craig et al. 2002). The most common breeds affected are the