[Multiple endocrine neoplasia type 2. Biological and clinical aspects].

CLASSIFICATION: Medullary thyroid carcinoma (MCT), a rare thyroid malignancy originating from the parafollicular C cell, may occur either as a hereditary or a non-hereditary entity. Hereditary MCT can occur either alone, familial MCT (FMCT), or in multiple endocrine neoplasia type 2 (MEN 2), associated with other endocrinopathies such as pheochromocytoma and/or hyperparathyroidism (MEN 2A and 2B). These hereditary disorders are due to germline mutation in the RET proto-oncogene. Early diagnosis and treatment significantly improve the outcome of patients with MCT.

DIAGNOSIS: In hereditary MTC, the MTC is usually multifocal and bilateral. Serum calcitonin measurement, a marker of disease, is superior to fine needle aspiration cytology in suggesting the diagnosis of MCT. Other investigations including ultrasonography, chest X-ray, computerized tomography and MRI may provide valuable topographic details in the assessment of the location and size of the primary tumor and metastases. The adrenomedullary disease is usually multicentric and bilateral, often detected after the onset of MCT; this disease is sought by measurement of urinary metanephrines and fractionated catecholamines. The tumor should be localised by computed tomography or MRI scans; 131I-MIBG scintigraphy is used to confirm diagnosis. Primary hyperpathyroidism generally have no symptoms, although hypercalciuria and renal calculi may occur; we screen for this disease by measurement of serum calcium, once hypercalcemia is documented, serum intact PTH should be measured to confirm the diagnosis. High-resolution small part sonography is sometimes used to differentiate parathyroid hyperplasia from solitary adenoma.