Canine hypothyroidism is very similar to HashimotoÕs lymphocytic thyroiditis in humans, which has been shown to be associated with major histocompatibilty (MHC) tissue antigens. A study of canine MHC genes has identified a particular MHC allele, DLA-DQA1*00101, in dogs with autoimmune thyroiditis, which doubles the risk of these dogs developing hypothyroidism. This rare DLA class II haplotype was found in affected Doberman pinschers, English setters, and Rhodesian ridgebacks, but was not present in affected boxers.

Several breeds (Siberian husky, shih tzu, Yorkshire terrier), not represented in the disease group, did not carry this DLA allele within their populations. Discovery of this genetic marker could provide a useful tool for selecting breeding stock to reduce the incidence of thyroiditis in pure-bred dogs.

References: Kennedy et al, Tissue Antigens 67:53-56, 2006; Happ et al, AKC Can Res Fdn Ann Report, 2005.

Parathyroid hormone (PTH) has been identified as a uremic toxin. It has been implicated in promoting progression of chronic kidney disease (CKD). Oral administration of low doses of calcitriol has been shown to reduce PTH in dogs with CKD. Uncontrolled clinical observations suggest that calcitriol therapy may prolong survival in dogs with CKD.

A double-masked, randomized, controlled clinical trial was performed to test the hypothesis that calcitriol reduces mortality in dogs with CKD. Thirty-seven client owned dogs with serum creatinine concentrations ranging from 2.0 to 6.3 mg/dl were enrolled. All dogs were > 1 year old and had stable creatinine values. They were randomly assigned to calcitriol (n = 18) or placebo (n = 19) and followed for 1 year. Initial mean serum creatinine values did not differ between groups (placebo = 4.00 ± 0.74; calcitriol = 4.08 ± 1.62). Calcitriol dosage, initially 2.5 ng/kg, was adjusted within the range of 0.75 to 5.0 ng/kg/day according to serial determinations of ionized calcium and PTH. Except for calcitriol, patient management was similar for both groups.

Calcitriol therapy was associated with a significant reduction in all-cause mortality (p = 0.036). All cause mortality rate was 63% in the placebo group and 28% in the calcitriol group. Median survival time was 365 days for dogs receiving calcitriol and 250 days for dogs receiving placebo. Thus, calcitriol appears to be effective in prolonging survival in dogs with stages 3 and 4 CKD.
Note: It does not appear to be of benefit in cats with CKC.

Reference: Polzin et al, ACVIM Forum, 2005.

Forty-five client owned cats were randomly assigned to a maintenance diet or a renal diet and evaluated tri-monthly for up to 24 months. Survival analyses were used to evaluate efficacy of the renal diet compared to the maintenance diet in minimizing uremia, renal-related mortality, and all causes of mortality.

Serum urea nitrogen concentrations were significantly lower and blood bicarbonate concentrations were significantly higher in the group fed the renal diet at baseline and during the 12- and 24-month intervals. Cats fed the maintenance diet had a significantly greater number of uremic episodes (22%) compared to cats fed the renal diet (0%). A significant reduction in renal-related mortality was observed in cats fed the renal diet.

The renal diet evaluated here was superior to an adult maintenance diet in minimizing uremic episodes and mortality rate in cats with mild to moderate spontaneous chronic renal failure.

Reference: Ross et al, ACVIM Forum, 2005.