Vitamin D-dependent non-type 1, non-type 2 rickets in a 3-month-old Cornish Rex kitten

Abstract

CASE PRESENTATION AND ASSESSMENT: A 3-month-old female Cornish Rex kitten was found to have non-painful swelling of the carpal and tarsal regions when presented for routine neutering. The kitten was smaller in stature and less active than its siblings and, according to the owner, had a bunny-hopping gait, was reluctant to climb stairs and strained during defecation. Radiography of the affected limbs and a subsequent radiographic survey of the entire skeleton demonstrated features consistent with rickets. The three littermates were clinically and radiographically normal. As a nutritionally complete diet was being fed, it seemed most likely that the kitten had an inborn error related to vitamin D metabolism. Serum biochemistry demonstrated reduced total alkaline phosphatase activity and increased concentrations of parathyroid hormone. Concentrations of 1,25- and 25-hydroxycholecalciferol were markedly reduced, confirming the diagnosis of rickets.

Treatment: The kitten was treated with calcitriol, administered orally once daily, and improved rapidly both clinically and radiologically. Serial laboratory studies suggested that the error in vitamin D metabolism was transient, and, at the time of writing, as an adult, the cat appears to require no ongoing replacement calcitriol therapy.

Clinical relevance: This case emphasises the value of examining a full 'calcium profile' via a human or veterinary reference laboratory, and a favourable prognosis in some kittens with rickets makes such investigations worthwhile. Even when finances preclude detailed investigation, trial therapy using a nutritionally complete diet and physiological doses of calcitriol or cholecalciferol is inexpensive and can produce a good response.

FIG 1

(a) Antebrachia of the affected kitten. (b) Close-up image showing prominent swelling in the carpal region (arrow)

FIG 2

(a,b) Lateral and craniocaudal radiographs of the affected kitten's distal limb. Note the widened growth plates (white arrowheads) and mushroomed metaphyses (black arrowheads) of the distal radius and ulna. (c) A craniocaudal radiograph of a normal littermate is presented for comparison; note the greater overall bone density and the narrower physes

FIG 3

Craniocaudal radiographs of the affected kitten's distal limb before and during calcitriol therapy. Note how the diffuse osteopenia observed prior to therapy is not evident in the images taken during therapy; the bone cortices have also become much denser. The irregular widened growth plates, so prominent prior to therapy, have become progressively ‘filled in’ during therapy, while the mushroomed metaphyseal regions are gradually remodelled into a more normal appearance

FIG 4

The cat at 22 months old (February 2011). Note the normally proportioned limbs, with no evidence of residual deformity