The Geriatric Cat: Diseases and Thyroid Dysfunction

Mooney, Carmel T (1994) The Geriatric Cat: Diseases and Thyroid Dysfunction. PhD thesis, University of Glasgow.

Abstract

This study describes the previous and current prevalence of medical diseases affecting geriatric cats in a referral population. Abnormalities of circulating thyroxine (T4) concentrations are described in sick cats and a simplified approach to treatment of hyperthyroidism with radioactive iodine (131I) evaluated. There was an increase in the number of cats presented at Glasgow University Veterinary School from, 417 between 1970 and 1972, to 835 between 1990 and 1992. Of these, 57 (13.7 %) cats of five years of age or over were referred as medical cases in the former time period, whereas 162 (19.4 %) were referred in the latter period. The most common disorders recognised between 1970 and 1972 were systemic neoplasia (21.1 %), gastrointestinal disease (19.3 %) and renal disease (8.8 %). The most common disorders diagnosed between 1990 and 1992 were hyperthyroidism (51.2 %), systemic neoplasia (10.5 %), viral infections (8.0 %) and renal disease (3.7 %). There was no conclusive clinical evidence of hyperthyroidism in cats between 1970 and 1972. Geriatric cats examined between 1970 and 1972 were significantly (P < 0.001) younger (mean +sd, 8.4 +4.0 years) than those seen between 1990 and 1992 (11.7 +3.3 years). Cats may now be living longer; the emergence of hyperthyroidism may be related in part to this increased longevity. A pre-precipitated total T4 antibody radioimmunoassay kit and a free T4 equilibrium dialysis kit were validated for use with cat serum. The mean +sd (reference range) serum total T4 concentration in healthy cats (n = 50) was 26.00 +7.62 (10.75 - 41.25) nmol/1. The serum free T4 concentration (n = 38) was 24.79 +8.33 (8.14 - 41.45) pmol/1. The calculated free T4 fraction was 0.10 +0.06 (range, 0.04 - 0.37) %. In cats with non-thyroidal illnesses (n = 107), serum total T4 concentrations (mean +sd, 17.35 +8.49; range, 2.00 - 45.33 nmol/1) were significantly (P < 0.001) lower than in healthy cats. There was a significant (P 0.001) inverse correlation between mortality and serum total T4 concentrations. Serum free T4 concentrations (mean +sd, 27.70 + 13.53; range 1.52 - 75.54 pmol/1) were not significantly (P > 0.05) different compared to healthy cats. Three cats (3.1 %) had serum free T4 concentrations below the reference range. Corresponding serum total T4 concentrations were also depressed. Twelve cats (12.2 %) had serum free T4 concentrations above the reference range. Corresponding serum total T4 concentrations tended to remain within the reference range. The calculated free T4 fraction in the sick cats (mean +sd, 0.24 +/-0.30; range, 0.06 - 2.10 %) was significantly (P < 0.001) elevated compared to healthy cats. Serum total T4 concentrations (mean +sd, 164.02 +102.10; range, 39.69 - 575.57 nmol/1) were significantly (P < 0.001) higher in hyperthyroid (n = 95) compared to healthy cats. The serum total T4 concentration was not diagnostically elevated in three (3.2 %) hyperthyroid cats. The specificity, sensitivity and efficiency of serum total T4 estimations for diagnosing hyperthyroidism in this population were 100, 96.9 and 98.5 %, respectively. Serum free T4 concentrations (mean +sd, 233.32 + 177.08; range, 46.88 - 687.61 pmol/1) were significantly (P < 0.001) higher in hyperthyroid (n = 26) compared to healthy cats. The serum free T4 concentration was not diagnostically elevated in one (3.8 %) hyperthyroid cat. The specificity, sensitivity and efficiency of this test were 93.9, 96.2 and 94.4 %, respectively. There was a highly significant correlation (r = 0.92, P < 0.001) between serum total and free T4 concentrations in the healthy and hypeithyroid cats. There was no significant (P > 0.05) difference in free T4 fractions between hyperthyioid (mean +sd, 0.11 +0.04; range, 0.07 - 0.25 %) and healthy cats. A simple method of dose estimation was devised based on clinical severity of the thyrotoxicosis, serum total T4 concentration and size of goitre. The mean +sd dose of administered to 50 cats was 143 +24 MBq. The treatment was effective in 47 (94 %) cats. There was no significant (P > 0.05) difference in the outcome between cats in which was injected intravenously (n = 27) or subcutaneously (n = 23).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Nash Andrew
• Keywords: Veterinary science
• Date of Award: 1994
• Depositing User: Enlighten Team
• Unique ID: glathesis:1994-76332
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 15:35
• Last Modified: 19 Nov 2019 15:35
• URI: https://theses.gla.ac.uk/id/eprint/76332