Prevalence of Marine-Lenhart syndrome on 99mTc-thyroid scintigraphy and response to radioiodine: A single institutional retrospective study

Marine-Lenhart Syndrome is a rare entity, described as Graves' disease with coexisting functioning thyroid nodules. It is often diagnosed on thyroid scintigraphy as a cold nodule with surrounding extranodular hyperactivity initially and postradioiodine ablation, they regain function on the follow-up thyroid scintigraphy due to endogenous thyroid-stimulating hormone (TSH) stimulation. We retrospectively reviewed all thyroid scintigraphy database performed between January 2018 and March 2020 in our institute. We searched patients with Graves' disease with the following criteria to suggest Marine-Lenhart Syndrome: (a) initial thyroid scintigraphy showing features of Graves' disease with coexistent poorly functioning nodules (b) There is normalization of uptake within the nodule on thyroid scan after radioiodine ablation suggestive of endogenous TSH stimulation (this also indirectly proves nodules are TSH dependent), (c) nodule(s) is/are benign on fine-needle aspiration cytology. Four patients (1.46%) were confirmed as Marine-Lenhart Syndrome as per the criteria. Three patients were female, and one was male. The eye signs were present in two of four patients. Two patients had two hypofunctioning nodules, whereas the remaining two had a single nodule and required re-ablation with radioiodine. Marine-Lenhart Syndrome requires special attention as these patients are relatively radioiodine resistant, require higher activity for iodine-131; however, it is curable with radioiodine treatment.