Clinical history A 14 year old male neutered house cat presented with a persistent swelling on the right antebrachium - this injury has been present for 3 months with only minimal change in size. Radiographs were made of the right forelimb. What is your diagnosis? Radiographic changes
- Changes in the radius
- Both cortical shadows and medullary cavity are poorly identified but have an appearance that suggests bony repair
- Periosteal new bone has an intact border and does not show signs of activity
- A small, well-defined focal lucency is noted in the cortex of the distal radius caudally and laterally
- Changes in the ulna
- The ulna appear radiographically normal without a similar pattern of productive/destructive radiographic changes
- The elbow joint has increased width with the trochlea appearing displaced proximally suggesting a shortened radius
- A small opacity of bone density is present dorsal to the radial carpal bone - the radiocarpal joint space is identified - the carpal bones do not appear to be in a normal alignment
- Soft tissue swelling is uniform throughout the antebrachium
Radiographic diagnosis
- The pattern of destruction/production in the distal radius is suggestive of a malignant bone tumor but involves over 1/2 of the radial shaft
- The absence of an aggressive periosteal new bone plus the apparent well-structured bony repair supports a benign lesion possibly suggestive of a chronic osteomyelitis
- The absence of change in the ulna when compared with the marked change in the radius does not support a history of bone trauma such both bones would be expected to have been fractured
- Involvement of only one bone plus the age of the cat rules out developmental or metabolic lesions
- While the lesion does not appear as an acute bone infection, it could be a chronic lesion that has remained active within the radius producing a reparative lesion
- The tentative diagnosis was that of a chronic osteomyelitis
- See comments
Comments
- A more detailed history was obtained from the owner relative to the earlier injury- it was probable that the cat received a bite wound, had an active osteomyelitis that was inadequately treated and developed into a chronic osteomyelitis that affected the entire radial shaft - an abscess and phlegmonous cellulitis developed quickly at the time of first presentation and may have influenced the manner in which the entire radius was affected
- The radiographic appearance is in agreement with this diagnosis
- Often an infectious lesion spreads to an adjacent bone or even to an adjacent joint space - that did not happen in this cat
- The pattern of presentation of the carpal bones suggests a possible trauma with fracture/subluxation
- The patient was placed on antibiotic therapy and improved clinically
- A lesion with such modeling of the cortex and medullary cavity in an older patient is always suspect for malignant tumor - these are less common in cats
- The clinical history in this patient was important in reaching the diagnosis of a chronic bone infection
