Thyroid scan in the diagnosis of Marine-Lenhart syndrome

Learning Objectives To review the pathogenesis and management of Marine-Lenhart syndrome, and to describe thyroid scan with correlation to other imaging modalities.

Graves' disease with accompanying functioning nodules is known as Marine-Lenhart syndrome. The syndrome is rare with a reported prevalence between 2.7% to 4.1%. The pathogenesis of Marine-Lenhart syndrome is the coexistence of a TSH dependent nodule(s) and Graves' disease. The existence of stimulating autoantibodies in patients with Graves' disease may play a role in the development of Marine-Lenhart syndrome. In addition to measurement of TSH and stimulating autoantibodies, diagnosis of Marine-Lenhart syndrome is based on the appearance of thyroid scan and ultrasound. In Marine-Lenhart syndrome, there is diffusely increased uptake in the gland with foci of nodules which appear as cold areas on thyroid scans because of TSH suppression associated with Graves' disease. Following I-131 therapy, however, the nodules may persist and accumulate radiotracer as the TSH level starts to rise. Biopsy of cold nodules in patients with Grave's disease should still be considered strongly as up to 9% are malignant. Recent data showed a 25-30% rise in the prevalence of nodules in Graves’ disease patients treated with radioiodine-131 and thyroid medication. On thyroid scan, a high percentage of these nodules are hypoactive (more than 95%), and a small percentage of these subjects have hyperactive nodules. Thus, these subjects have thyrotoxicosis secondary to both Graves' disease and toxic nodular goiter. Cases represented illustrate the use of thyroid scan in the management of this syndrome