1) What is your assessment of thyroid uptake?
Although there is clearly uptake throughout the thyroid and only slightly less than in salivary glands, there is clearly increased background activity in comparison, implying reduced thyroid uptake overall.
2) What do A and B represent – can you guess the missing clinical information?
This represents intense tracer accumulation in the breasts. Such intense uptake is only really seen in the lactating breast, due to huge upregulation of the sodium iodide symporter in response to hormonal stimulation. This patient was 5 months post-partum and breastfeeding.
3) What is the complete diagnosis?
The reduced thyroid uptake in this clinical scenario indicates a diagnosis of post-partum thyroiditis. Graves’ disease may also present for the first time with thyrotoxicosis in the post-partum period but diffusely increased thyroid uptake would be expected. It is worth noting that quantitative thyroid uptake with pertechnetate is unreliable in this setting due to competitive uptake by the breasts.
4) What is the natural history of this condition?
Post-partum thyroiditis occurs in the first year after delivery in 5-10% of pregnancies. It is probably an immune-mediated phenomenon, supported by there being an increased risk of this disorder in women with thyroid autoantibodies (anti-thyroid peroxidase) and other autoimmune conditions such as type I diabetes. The biggest risk factor of all is having had post-partum thyroiditis with a previous pregnancy. Classically there is a phase of hyperthyroidism followed by a phase of hypothyroidism, each lasting a few months. Some patients will experience only one of these phases. In any event, thyroid function usually returns to normal within 12-18 months, but 25-30% of patients will subsequently develop chronic hypothyroidism over the next 5 years.
5) What are the radiation protection issues when performing thyroid scintigraphy in this setting?
As well as the usual radiation protection considerations for the patient and staff, special consideration must be made for the baby. The accumulation of pertechnetate in breast milk means that breastfeeding should be suspended for a period, and in the UK ARSAC recommend a period of 24 hours for a standard 80MBq pertechnetate dose. Mothers should be given enough notice prior to the study to allow them to store sufficient expressed milk or make alternative arrangements with formula , and during the 24 hours after the study they should express and discard breast milk at intervals.
References
- Muller AF, Drexhage HA, Berghout A. Postpartum thyroiditis and autoimmune thyroiditis in women of childbearing age: recent insights and consequences for antenatal and postnatal care. Endocr Rev 2001; 22(5):605-30
- Administration of Radioactive Substances Advisory Committee. Notes for Guidance on the Clinical Administration of Radiophamaceuticals and Use of Sealed Radioactive Sources 1998.
Contributed by Ian Hagan
The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.