Serum Cobalamin and Methylmalonic Acid Concentrations in Hyperthyroid Cats Before and After Radioiodine Treatment

Abstract

BackgroundHyperthyroidism, the most common endocrine disorder in cats, has been associated with low serum cobalamin concentrations. Whether this is a functional cobalamin deficiency of clinical importance has not been assessed.Hypothesis/ObjectivesCats with hyperthyroidism experience a functional cobalamin deficiency which correlates with their clinical catabolic state and is reversible with return of the euthyroid state.AnimalsThirty‐nine client‐owned hyperthyroid cats.MethodsProspective observational study. Serum cobalamin, methylmalonic acid, and clinical scores were determined in each hyperthyroid cat at enrollment and when euthyroid (60 days after radioiodine treatment).ResultsFive of the 39 hyperthyroid cats (13%) had a low serum cobalamin concentration ranging from <150 to 290 ng/L. Serum cobalamin concentrations normalized to >350 ng/L in 2 of the hypocobalaminemic cats once euthyroid. None of the hyperthyroid/hypocobalaminemic cats had increased serum methylmalonic acid concentrations (175–601 nmol/L). In cats with clinical and biochemical hyperthyroidism, there was no correlation between serum cobalamin concentrations with total T4 concentration (P = .12) or clinical scores including body weight (P = .11) and BCS (P = .54).Conclusions and Clinical ImportanceIn this population of hyperthyroid cats, the prevalence of hypocobalaminemia was low. Specifically, hyperthyroid cats, in which concurrent gastrointestinal disease is unlikely. Hypocobalaminemia is not a functional deficiency requiring supplementation in hyperthyroid cats without gastrointestinal disease.

Effects of 6 Weeks of Parenteral Cobalamin Supplementation on Clinical and Biochemical Variables in Cats with Gastrointestinal Disease

“…It has recently been shown that hypocobalaminemia in cats with hyperthyroidism, in which underlying gastrointestinal disease is unlikely, is not a functional deficiency requiring supplementation . In contrast, all four hyperthyroid cats in the present study also had biochemical evidence of Cbl deficiency.…”

“…In contrast, all four hyperthyroid cats in the present study also had biochemical evidence of Cbl deficiency. This difference probably is a reflection of variances in inclusion criteria; we deliberately aimed to select cats with gastrointestinal disease, whereas the other study excluded cats suspected of having or diagnosed with gastrointestinal disease …”

“…Although it is not known when depletion of cellular Cbl stores and increases in MMA levels begin in the course of subnormal serum Cbl concentrations, MMA is currently considered the best indicator of Cbl status in cats . Studies examining biochemical Cbl deficiency in cats have focused on serum MMA concentration, and urine MMA concentration has been only sporadically reported . In humans, a linear relationship exists between serum and urine MMA concentrations .…”

Cobalamin (Vitamin B12) – Diagnostische und therapeutische Bedeutung in der Kleintiergastroenterologie

“…Diese kann mit niedrigen Cobalaminkonzentrationen im Serum einhergehen (Prävalenz ca. 40%) 24 . Allerdings handelt es sich bei hypocobalaminämischen Katzen mit unbehandelter Hyperthyreose, sofern nicht gleichzeitig eine chronische gastrointestinale Erkrankung oder EPI vorliegt, nicht um einen funktionellen Cobalaminmangel (d. h. auf zellulärer Ebene) und verlangt daher nicht zwangsläufig eine Supplementation 24 .…”

Effect of age, sex and body weight on the serum concentrations of cobalamin and folate in cats consuming a consistent diet

“…1,7 In addition to typical disease associations, some authors have suggested that feline cardiomyopathy, arterial thromboembolism and hyperthyroidism are associated with decreased serum cobalamin concentrations; 8,9 although a recent study found that the prevalence of hypocobalaminaemia in hyperthyroid cats was low, while folate was significantly lower in hyperthyroid cats compared with when the same cats were euthyroid post-radioiodine treatment. 10 Lastly, congenital abnormalities impeding cobalamin absorption have been reported, albeit rarely, in cats. 11,12 Factors other than disease have been found to have an effect on cobalamin and folate serum concentrations.…”