From the Guidelines
Elevated Thyroid Peroxidase (TPO) and Thyroid Stimulating Immunoglobulin (TSI) levels are indicative of an immune-mediated thyroid disorder, and the patient should be managed conservatively with close monitoring of thyroid function and initiation of thyroid hormone replacement therapy when necessary, as recommended by the Society for Immunotherapy of Cancer (SITC) toxicity management working group 1. The presence of elevated TPO and TSI levels suggests an autoimmune thyroiditis, which can lead to thyrotoxicosis and eventually hypothyroidism.
Key Considerations:
- Thyroiditis is a self-limiting process, but it can lead to permanent hypothyroidism after an average of 1 month after the thyrotoxic phase and 2 months from initiation of immunotherapy 1.
- Conservative management during the thyrotoxic phase of thyroiditis is sufficient, and non-selective beta blockers may be needed in symptomatic patients 1.
- Repeat thyroid hormone levels should be performed every 2–3 weeks, and thyroid hormone replacement therapy should be initiated at the time of hypothyroidism diagnosis 1.
Management Approach:
- Monitor thyroid function closely: Repeat thyroid hormone levels every 2–3 weeks to assess for development of hypothyroidism.
- Initiate thyroid hormone replacement therapy: Start thyroxine 0.5-1.5 μg/kg (start low in elderly, if cardiac history) when hypothyroidism is diagnosed, as recommended by the European Society for Medical Oncology (ESMO) clinical practice guidelines 1.
- Manage symptoms: Use propranolol or atenolol for symptoms of hyperthyroidism, and consider carbimazole if anti-TSH Receptor Ab positive 1.
- Continue immune checkpoint inhibitor therapy: Unless the patient is unwell with symptomatic hyperthyroidism, in which case the therapy should be withheld until symptoms are controlled 1.
From the Research
Implications of Elevated TPO and TSI Levels
- Elevated Thyroid Peroxidase (TPO) and Thyroid Stimulating Immunoglobulin (TSI) levels are associated with autoimmune thyroid disease (AITD) 2
- AITD can result in dysfunction of the thyroid gland, including hyperfunction, hypofunction, or both 2
- Elevated TPO levels are a hallmark of AITD and are present in almost all patients with Hashimoto's thyroiditis, in two-thirds of patients with postpartum thyroiditis, and in 75% of patients with Graves' hyperthyroidism 2
- TSI levels are specific for Graves' disease and can stimulate the TSH receptor, causing hyperthyroidism 3, 4
- Elevated TPO and TSI levels can be associated with a range of clinical presentations, including Graves' disease, Hashimoto's thyroiditis, and subacute thyroiditis 3, 4
- In some cases, elevated TPO levels may be associated with other autoimmune disorders, such as multiple system atrophy (MSA) 5
- The presence of elevated TPO and TSI levels can indicate a switch from blocking to stimulating autoantibodies, leading to changes in the patient's euthyroid state 3
- Elevated TPO and TSI levels can be used as diagnostic markers for AITD, but their presence does not necessarily predict the clinical course of the disease 2, 3, 4
- Treatment with anti-thyroid drugs can decrease TPO and TSI levels, but may not eliminate them completely 6