What is Your Diagnosis? (Bilateral Forelimb Deformity and Abnormal Gait in a Young Devon Rex)

What is Your Diagnosis?

An 8-month-old, intact female Devon Rex cat was presented to the University Veterinary Centre, Sydney with bilateral forelimb deformity and an abnormal gait. The deformities had been present at birth and resulted in dystocia (a caesarean section was not necessary). She had been the only kitten in the litter and it was unknown if either parent had produced other abnormal offspring from prior matings.

The cat appeared bright and responsive. She was well grown and had a good appetite. Both forelimbs had a varus deformity at the carpus and a medial angulation of the forearm. She stood with her elbows abducted and flexed and walked with a squatted, stiff gait due to the medial angulation of the antibrachii and carpi and the restricted range of elbow movement (this was not quantitated with goniometry). Neither limb could be straightened fully with manipulation, due to contracture of the medial tendons and muscles, as well as the bony deformity. The carpi could not be straightened, nor the elbows fully extended, however they did not appear unstable and neither was painful on palpation or manipulation. The first digits of both front paws were absent and the cat had a short, stiff tail. The hindlimbs and rest of the physical examination were unremarkable.

Fig 1.

Fontal view of fore limbs. Note the varus deviation and foreshortening of antibrachii.

Fig 2.

Craniocaudal radiographs of both forelimbs.

Fig 3.

Mediolateral radiographs of both forelimbs.

Examine the photographs of the cat and the radiographs of the thoracic limbs and tail and consider the following questions.

• What is your diagnosis based on the history, physical findings and interpretation of the radiographs?

• What is the treatment and likely prognosis for this condition?

Radiographic interpretation

The radius is absent bilaterally and the ulnae are thickened and misshapen, curving cranially and medially. The humeroulnar articulation is incongruent with shallow trochlear notch and increased opacity in the adjacent subchondral bone bilaterally, indicative of sclerosis. Periarticular mineral opacities are present adjacent to the humeral condyles and the coronoid processes of the ulnae, consistent with osteoarthritis. The distolateral aspect of the ulna is misshapen also, with an undulating medial to lateral slope apparently accommodating the proximal aspect of the adjacent cuboidal bones of the carpi bilaterally. The medial aspect of the radialcarpal bone is absent, as are the phalanges of the first digit bilaterally. The coccygeal vertebrae II-IX are fused in a helical fashion.

Discussion

Radial agenesis is defined as the congenital underdevelopment or absence of the radial structures of the forearm (James et al 1999). In humans it is well documented and classification schemes based on the severity of the deformity have been described (James et al 1999). Radial agenesis is the most frequent hemimelia reported in the dog and cat. Although involvement of a single limb is most common, bilateral cases have been reported in two families of Chihuahua (Alonso et al 1982) and two related cats (Swalley & Swalley 1978). Total absence of the radius is often accompanied by complete or partial absence of the radial carpal bone and first digit (Johnson & Watson 2000).

Since the radius is the main weight-bearing bone of the forearm its absence usually results in severe deformity and impaired function. The ulna becomes thickened and curved due to increased load bearing, and the paw develops a varus deformity because of loss of medial support structures and contracture of extensor tendons (Betts 1981). The elbow joint is also affected due to the presence of humeroulnar subluxation secondary to lack of support from the radial head (Johnson & Watson 2000).

Many factors may affect the embryonic development of the forelimb and the pathogenesis of radial agenesis in both humans and domestic species is not well understood. The trait may be heritable in some cases (Alonso et al 1982), and although this has not been confirmed with test matings, there are anecdotal reports of the trait being produced by the deliberate breeding of some polydactyl cats (www.cfainc.org/comments-twistykats.html). Another hypothesis is that hemimelia results from an injury to the neural crest by a teratogen in utero and that the pattern of deformity follows the distribution of sensory nerves. It is proposed that the sensory nerve tissue exerts a trophic effect on the developing embryonic limb tissues, and therefore in their absence normal development does not occur (Winterbotham et al 1985). Various aetiological factors have been proposed, including inflammatory or infectious conditions, vaccines, maternal disease, malnutrition and various drugs, for example, Thalidomide (Lewis & Van Sickle 1970, Winterbotham et al 1985).

Radiographic documentation of absent or hypoplastic radial structures (radius, radial carpal bone and/or the first digit) is necessary to confirm the diagnosis. Complicating factors such as fractures, dislocations or other skeletal anomalies may also be detected using this imaging modality.

Treatment of choice for a unilaterally affected animal is considered to be limb amputation (Manley & Amundson 1993). Obviously, bilaterally affected individuals present a much greater challenge. Treatment in humans is aimed at minimising the angular deformity, and thereby produce a more aesthetically acceptable limb, rather than to improve limb function. Various attempts to surgically improve the varus deviation have been reported in dogs and cats (Swalley & Swalley 1978, Pedersen 1968); however, these have not been shown to be effective. Euthanasia may be necessary if limb function is severely affected bilaterally. In this particular case the cat was left untreated, as she was able to function reasonably well. Although she will most probably develop severe degenerative joint disease in the future, her quality of life was considered to be acceptable at this stage.