Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 583
Joint space widening, described as an early radiographic change, and joint space collapse,
as a late change, have been reported in infectious arthritis. Recognition of these
changes is difficult because of the variation resulting from patient restraint and positioning
during radiography.
Bacterial and fungal infectious arthritis produce similar radiographic changes. Only
soft-tissue swelling has been described in mycoplasma and viral arthritis. 626,627 In visceral
leishmaniasis, the joint changes described were similar to those of degenerative
joint disease. 311 Another form of septic arthritis seen in juvenile dogs affects both physes
and joints and is referred to as puppy strangles. 631-633 Typically multiple sites are
affected.
Immune-Mediated Arthritis. Numerous systemic disorders have been associated with
immune-mediated arthritis in dogs and cats. These conditions may be classified radiographically
into two major categories: erosive and nonerosive.
Erosive Arthritis
CANINE RHEUMATOID-LIKE ARTHRITIS. Canine rheumatoid-like arthritis is the most frequently
described erosive arthritis. 623,634-640 The carpal and tarsal joints are affected most
frequently, although any joint may be involved (Fig. 4-136). The condition may be
monoarticular, although polyarticular involvement is more common and joint involvement
usually is symmetric. Soft-tissue swelling and loss of bone density around the joint
are evident early in the disease. The trabecular pattern of the distal radius, ulna, tibia,
fibula, and carpal and tarsal bones becomes coarse due to a loss of the finer secondary trabeculae.
That portion of the distal radius and distal tibia within the joint capsule area will
be affected. Round, cystlike lucencies may develop within the subchondral bone.
Progressive subchondral bone destruction occurs, especially at the articular margins. The
joint space width becomes irregular and joint deformity and subluxation may occur.
GREYHOUND POLYARTHRITIS. A specific erosive polyarthritis has been described in
Greyhound dogs 3 to 30 months of age. 426,427,641 The radiographic and pathologic changes
are similar but less severe than those of canine rheumatoid-like arthritis.
FELINE PROGRESSIVE POLYARTHRITIS. A progressive polyarthritis has been described in
mature cats, predominately in males, and has been linked to feline leukemia and feline syncytial
virus. 642-644 The disease is characterized radiographically by joint swelling, periarticular
and subchondral erosions, and joint deformity. In most cases, bony proliferation is
observed adjacent to the affected joints (Figs. 4-137 and 4-138).
Nonerosive. Nonerosive immune arthritis is characterized radiographically by softtissue
swelling without erosive bony changes despite long-standing disease. Some loss of
bone density may be observed; however, the subchondral bone and periarticular margins
appear normal (Fig. 4-139). This form of immune arthritis has been associated with idiopathic
causes; systemic lupus erythematosus; chronic inflammatory, infectious, or parasitic
diseases; and some drugs. 645-651 The offending organism does not have to be present within
the joint. A juvenile onset nonerosive polyarthritis has been reported in Akitas. The condition
is thought to be inherited. 652
Crystal-Induced Arthritis. Crystal-induced arthritis is extremely rare. Both gout urate
crystal deposition in the joints and calcium pyrophosphate dihydrate (CPPD) deposition
disease, or pseudogout, have been reported in dogs. 653-657
CPPD deposition disease usually is associated with the deposition of amorphous aggregates
of radiodense mineralizations in the soft tissues of the joint. 654-656 CPPD deposition
disease in Great Danes can result in the deposition of mineral deposits in the synovial joints
of the appendicular and axial skeleton. 653 Amorphous mineral opacities have been
reported in the diarthrodial joints of the cervical vertebral column in puppies and in the
diarthrodial joints of the cervical spine and extremities in a 1-year-old dog. 653 Abnormal
bone curvature, cortical thinning, increased medullary trabeculation, and shortening of
the long bones were noted also in the older dog.
Soft-tissue swelling with periarticular mineralization (punctate or fine linear patterns)
has been described. Extensive nodular soft-tissue mineralization was demonstrated around