Blood pressure in hyperthyroid cats before and after radioiodine treatment

Abstract

Background: Hyperthyroid cats commonly have systemic hypertension, with a reported prevalence of 7% to 48%. Although hypertension might be expected to resolve once treatment restores euthyroidism, it can persist or only first develop after treatment.

Objectives: To determine the proportion of hyperthyroid cats with hypertension (systolic blood pressure [SBP] ≥160 mm Hg), persistence or first development of hypertension after successful radioiodine treatment, and correlation of post-treatment hypertension with azotemia or hypothyroidism.

Animals: Four hundred one hyperthyroid nonazotemic cats were included in the study.

Methods: Prospective, cross-sectional and before-and-after studies. All hyperthyroid cats had SBP measured by Doppler; 255 had SBP rechecked 6 months after successful radioiodine (¹³¹I) treatment.

Results: Of untreated hyperthyroid cats, 108/401 (27%) were hypertensive. A higher proportion of hypertensive cats were nervous/excited compared with normotensive cats (47% vs 12%; P < .001). Of the initially hypertensive cats, 87/108 cats were reexamined after ¹³¹I treatment; 43/87 (49%) cats normalized SBP, whereas 44/87 (51%) remained hypertensive. Of the initially normotensive cats, 16/168 (9.5%) first developed hypertension after successful ¹³¹I treatment. 7/60 (12%) of the ¹³¹I-treated hypertensive cats were azotemic and 9/60 (15%) were hypothyroid. A higher proportion of cats remaining hypertensive had nervous/excited demeanor than did normotensive cats (50% vs 17%; P < .001).

Conclusions/clinical importance: Hypertension, when present, resolves in many hyperthyroid cats after successful treatment. Hyperthyroid cats uncommonly develop new hypertension after treatment. Persistent or newly detected hypertension was unrelated to azotemia or iatrogenic hypothyroidism. More frequently perceived nervousness/anxiety in radioiodine-treated hypertensive cats suggests that many of these cats might have "situational" hypertension, as hyperthyroid-induced hypertension should resolve after treatment.

Keywords: 131I; Doppler; feline; hypertension; hyperthyroidism; radioactive iodine.

FIGURE 1

Flowchart for enrollment of hyperthyroid cats in the before‐after study, separated into 3 thyroid outcome groups. The 3 clinics included the Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium; Iodocat, Madrid, Spain; and the Animal Endocrine Clinic, New York, New York, USA.

FIGURE 2

Boxplots of systolic blood pressure (SBP) measurements in 401 untreated hyperthyroid cats, divided into groups based on severity of disease, based on serum thyroxine (T₄) and triiodothyronine (T₃) concentrations. (A) SBP in 200 cats with serum T₄ < 9.4 μg/dL (blue box) versus 201 cats with serum T₄ ≥ 9.4 μg/dL (red box). (B) SBP in 200 cats with serum T₃ < 126 ng/dL (blue box) versus 201 cats with T₃ ≥ 126 ng/dL (red box). Boxes represent the interquartile range (IQR; 25th‐75th percentile). The horizontal bar in each box represents the median value. The whiskers indicate the range of data values unless outliers are present, in which case, the whiskers extend to a maximum of 1.5 times the IQR. Such outlying data points are represented by open circles. The dotted line indicates the SBP cutoff value of ≥160 mm Hg, above which indicates hypertension.

FIGURE 3

Boxplots of systolic blood pressure measurements in 401 untreated hyperthyroid cats, separated into 2 groups based on the temperament or demeanor score (ie, calm/anxious versus nervous/aggressive ⁴⁴ ). See Figure 2 for key.

FIGURE 4

Boxplots of systolic blood pressure (SBP) values in 255 hyperthyroid cats before and after treatment, divided into 2 groups based on their initial blood pressure category (normotensive vs hypertensive). (A) Before and after SBP in 168 initially normotensive cats. (B) Before and after SBP in 87 initially hypertensive cats. See Figure 2 for key.

FIGURE 5

Flowchart for changes in systolic blood pressure (SBP) category (hypertensive vs normotensive) in 255 hyperthyroid cats studied before and after ¹³¹I treatment.

FIGURE 6

Boxplots of posttreatment systolic blood pressure values in 255 cats, divided into the 211 nonazotemic cats and 44 cats with azotemia. See Figure 2 for key.

FIGURE 7

Boxplots of posttreatment systolic blood pressure values in 255 cats, divided into the 193 euthyroid cats and 62 cats with iatrogenic hypothyroidism. See Figure 2 for key.

FIGURE 8

Boxplots of systolic blood pressure (SBP) measurements in 255 hyperthyroid cats before and after treatment, separated into 2 groups based on the temperament or demeanor score (ie, calm/anxious vs nervous/aggressive ⁴⁴ ). (A) Pretreatment SBP in 2 demeanor groups. (B) Posttreatment SBP in 2 demeanor groups. See Figure 2 for key.