MTC in MEN2b is essentially the same as in MEN2a except that the disease is more aggressive, with metastases (spreading of the cancer) seen in infancy in some cases.
Medullary thyroid carcinoma is a cancer of the C cells of the medulla of the thyroid gland, which secrete excessive amounts of calcitonin. The MEN form of MTC is usually multifocal disease within the thyroid (as opposed to the solitary disease foci seen in non-MEN MTC). It also occurs at a younger age (as young as 2 years) but has better prognosis.
Thyroid pathology in MEN2b - click to enlarge
Diarrhoea occurs in 30% patients, associated with elevated blood calcitonin or tumour-related secretion of hormones such as serotonin and prostaglandins. In addition, ACTH may be produced ectopically, producing Cushing's syndrome (see relevant section of the Adrenal Gland for information on Cushing's). There may also be a swelling in the neck (a goitre) which may cause difficulty with swallowing (dysphagia).
Individuals may indeed be asymptomatic. In these cases, diagnosis is by screening with the pentagastrin test. Administration of pentagastrin causes a rise in calcitonin within 2-3 minutes in the presence of MTC.
When MEN is suspected, screening is very important as early detection of MTC allows curative surgery to be performed before the tumour spreads to adjacent tissues and lymph nodes. The whole thyroid and the nearby lymph nodes are removed (thyroidectomy with lymphadenectomy). In MEN2b, due to the disease being more aggressive than other forms, some advocate total thyroidectomy in infancy as soon as the child is able to withstand the trauma of surgery.
The success of the surgery may be monitored by checking blood calcitonin levels. Chemotherapy and radiotherapy have been of limited success in the treatment of MTC.
For much more information on medullary thyroid carcinoma and thyroid physiology please see the relevant parts of the 'Thyroid Gland' section of this website.