Does Marine Lenhart Syndrome really exist?

Primary hyperthyroidism is the result of overproduction of thyroid hormone resulting in the classic symptoms of tachycardia, weight loss, diaphoresis, and hyperdefecation. There are multiple common causes to include Graves’ disease, toxic multinodular goiter, and solitary toxic adenomas. Marine Lenhart Syndrome (MLS) is a rare cause of hyperthyroidism, caused by a coexistence of constitutively active thyroid nodules and Graves’ disease. In the original document of Marine and Lenhart, there is no distinction made between the autoimmune phenomenon of Graves’ disease and the solitary toxic nodule of Plummer’s disease. Rather they are both considered to be the manifestation of the same disease. However, in the current era of radionuclide technology, a clear distinction of MLS can be seen with diffuse uptake in the thyroid gland and focused enhancement in the toxic nodules. Therefore what was previously described as one entity is now distinct as Graves’ disease and Plummer’s disease. It is also becoming increasingly clear within the literature that there is also a new phenomenon of post-radioiodine immunogenic hyperthyroidism in patients with toxic nodules and elevated autoantibodies. Therefore in order to properly treat and manage patients, a new definition of MLS may need to be proposed.