# Comparison of the Changes in Quality-of-Life of Cats with Hyperthyroidism Treated with Radioiodine or Antithyroid Drugs—A Preliminary Study †

## TL;DR

This study compares how the quality of life of hyperthyroid cats improves over time with two different treatments, finding that both improve it, but it remains lower than in healthy cats.

## Contribution

The study provides preliminary evidence on longitudinal HRQoL changes in hyperthyroid cats treated with radioiodine or antithyroid drugs.

## Key findings

- Quality of life improved over time in hyperthyroid cats regardless of treatment type.
- HRQoL scores remained lower than in non-hyperthyroid cats even after treatment.
- Treatment type and thyroid hormone normalization had no significant impact on HRQoL improvement.

## Abstract

Cats with hyperthyroidism have reduced quality-of-life, but how this is affected by different treatment forms over time is unknown. This study examined how health-related quality-of-life changes in hyperthyroid cats receiving either curative radioiodine therapy or palliative antithyroid medication. Quality of life was evaluated using a validated questionnaire before radioiodine treatment or within six months of starting antithyroid drugs and re-assessed at follow-up one, three, and six months later, alongside thyroid hormone concentrations. The study revealed that cats’ quality-of-life improved over time, regardless of the treatment type or normalisation of thyroid hormone concentrations. However, even after treatment, quality-of-life remained lower than that of cats without hyperthyroidism. This study underscores the need for ongoing monitoring and care to ensure the best possible quality-of-life for affected cats.

A previous cross-sectional study found impaired health-related quality of life (HRQoL) in hyperthyroid cats, but the longitudinal impact of treatment—especially differences between radioiodine (RAIT) and antithyroid drug (ATD) approaches—remains unclear. This study aimed to evaluate changes in HRQoL in recently diagnosed (<6 months) hyperthyroid cats that underwent RAIT or received ATD. HRQoL was assessed using the validated HyperthyroidismQoL-cat questionnaire at baseline and after 1, 3, and 6 months, alongside thyroid status (eu-/hypo-/hyperthyroid) evaluation. Mixed-effects model analysed the influence of treatment type, timepoint, and thyroid status on log(HRQoL). HRQoL differences between groups at baseline and comparison to a non-hyperthyroid control group (n = 322) from a previous study at month 6 were examined using Mann–Whitney U tests. Data are presented as median (range), with significance set at p < 0.05. Thirty-eight client-owned hyperthyroid cats (15 ATD, 23 RAIT) were included. HRQoL scores at baseline did not differ between groups (RAIT: 103.5 [27–211], ATD: 73 [22–260], p = 0.22). HRQoL significantly improved over time (p < 0.001) but was not affected by treatment type (p = 0.20) or thyroid status (p = 0.40). Despite improvement, HRQoL remained lower than in non-hyperthyroid controls (hyperthyroid: 42.5 [3–161.5], non-hyperthyroid: 27 [0–249], p = 0.007). This study highlights the overall positive impact of treatment on HRQoL, but due to the lack of randomisation and heterogeneity of subjects and treatment, conclusion have to be considered preliminary.