# Effect of radioiodine treatment for Graves’ disease on the generation of TSH anti-receptor stimulating antibodies (TSI)

## TL;DR

Radioiodine treatment for Graves' disease increases TSI levels, which can stay high for over a year in many patients, affecting treatment and management decisions.

## Contribution

This study shows that TSI levels rise after radioiodine therapy and remain elevated in over half of patients for up to 12 months.

## Key findings

- TSI levels increased in 72% of patients after radioiodine therapy.
- TSI remained higher than baseline in 58% of patients at 12 months.
- Persistent TSI was more common in patients with thyroid eye disease, longer disease duration, or higher baseline TSI.

## Abstract

It is well established that serum levels of TSH receptor antibodies (TRAb)
rise after radioiodine (131I) therapy for Graves’ disease (GD). However, it
remains unclear whether these post-therapy autoantibodies are predominantly
TSH receptorstimulating immunoglobulins (TSI) and how their persistence
might affect treatment outcomes.

In this prospective study, 39 patients with GD underwent 131I
therapy. Serum TRAb (measured by competitive electrochemiluminescence,
ECLIA) and TSI (measured by an IMMULITE® 2000/2000 XPi TSI
assay) were evaluated at baseline and at 1, 2, 3, 6, 9, and 12 months
post-therapy. More than 7% increase from baseline was considered a
significant rise.

At diagnosis, all 39 patients tested positive for TRAb, while 38 tested
positive for TSI. Both TRAb and TSI levels rose significantly between months
2 and 4 post-131I, followed by a progressive decline by months 9
to 12. TSI increased in 72% of patients; of these, 93% showed a gradual
decrease but remained higher than baseline in 58% at 12 months. Patients
with thyroid eye disease (TED), longer disease duration, or higher baseline
TSI more frequently exhibited persistent elevation at one year. Despite the
persistence of TSI, all patients achieved control of thyrotoxicosis
(euthyroid or hypothyroid states).

Radioiodine therapy leads to an increase in TSI, which can remain elevated
for up to 12 months in more than half of GD patients. These findings suggest
potential benefits of measuring TSI for guiding management decisions,
particularly regarding antithyroid drug discontinuation and pregnancy
planning.