Dimetilarginina simmetrica (SDMA) nei gatti ipertiroidei

Hyperthyroidism and chronic kidney disease (CKD) are two of the most common disease in old-aged cat population. Hyperthyroidism leads to a decrease in serum creatinine (sCr) by increasing glomerular filtration rate (GFR) and decreasing body muscle mass. This can mask a concurrent CKD that might become evident after the onset of treatment. Symmetric dimethylarginine (SDMA) is a novel, early, renal biomarker independent of body muscle mass, therefore it might be a useful marker of renal disease in hyperthyroid cats. The aim of this study was to evaluate if SDMA was affected by hyperthyroidism and if it would change after methimazole treatment. Moreover, the aim was also to evaluate if SDMA could be a valuable biomarker for the early detection of patients that would develop CKD after methimazole treatment. Twenty-four hyperthyroid cats [serum total thyroxin (T4) >40 mmol/L] with normal sCr (<1.8 mg/dL) were included. Eighteen healthy cats, older than 7 years, with normal T4 and sCr <1.8 mg/dL were enrolled as control group. Data about physical exam, emogram, serum biochemistry and T4 concentrations were evaluated. SDMA was measured on the left over serum from previous analyzes and stored at -20°C. SDMA measurement was performed on serum samples collected at the time of diagnosis of hyperthyroidism and after methimazole treatment between 14 days to 3 months days after start of treatment; follow-up was available for 10/24 hyperthyroid cats. SDMA was measured using a validated immunoassay (IDEXX SDMA test). Hyperthyroid cats were older (p=0.001) and had a lower body weight (BW) (p<0.0001) than control cats. In hyperthyroid cats sCr was positively correlated with SDMA both at diagnosis and after treatment, but correlation was stronger after treatment (r=0.49, p=0.01 vs r=0.82, p=0.005). No correlation was found between SDMA and T4 at diagnosis (r=-0.32; p=0.12). In hyperthyroid cats BW was not correlated with sCr, nor with SDMA. There was no difference for sCr between hyperthyroid cats and controls at diagnosis (p=0.3). Creatinine (p=0.006) and BW (p=0.015) significantly increased after treatment. No difference was found when comparing SDMA in hyperthyroid and control cats both at diagnosis (p=0.11) and after treatment (p=0.28); however, SDMA decrease in 7/10 cats after treatment. Six hyperthyroid cats had SDMA value higher than reference range at diagnosis. In these cats follow-up after treatment was available for 2/6 only; in both these 2 cats when T4 was normal sCr was slightly increased and SDMA was decreased. Based on this study results feline hyperthyroidism seems not to influence SDMA concentration by itself. Correlation between SDMA and creatinine was confirmed also in hyperthyroid population. Further studies are needed to better define the role of SDMA as biomarker of CKD in hyperthyroid cats.