Latent subclinical medullary thyroid carcinoma: diagnosis and treatment.

Sporadic medullary thyroid carcinoma (SMTC) is usually diagnosed at a clinical stage often associated with lymph node involvement. Hence surgical treatment does not result in definitive cure in many patients. Studies have demonstrated that routine measurement of serum basal calcitonin (CT) in patients with nodular thyroid disease allows preoperative, early diagnosis of unsuspected SMTC. The aim of this work was to assess the results of surgery in patients operated on for subclinical SMTC detected preoperatively by measurement of serum CT. Results were compared with those obtained in patients with SMTCs diagnosed at a clinical stage and operated on during the same period. During a 4-year period (1993-1996) 24 SMTCs were diagnosed and treated in our department. They were diagnosed at a clinical stage in 13 patients (group 1): palpable thyroid tumor (n = 11), palpable metastatic lymph node (n = 6), distant metastases (n = 4). In nine cases the diagnosis was made by both fine-needle aspiration cytology and serum CT measurement. In the four other cases the initial cytology was incorrect, but the diagnosis was revised on the basis of elevated basal CT values. In 11 patients (group 2) presenting with nodular thyroid disease, SMTC was not clinically detectable. SMTC was preoperatively suspected by elevated CT levels: basal CT > 10 pg/ml and pentagastrin-stimulated CT peak > 100 pg/ml. One patient in group 1 with distant metastases was not operated on. All of the other 12 patients underwent total thyroidectomy and extensive lymph node dissection. The mean size of the tumors was 27 mm. Lymph node involvement was found in nine patients. After surgery, CT levels returned to normal in five patients but remained elevated in five others; the two remaining patients died of distant metastases. All 11 patients in group 2 underwent total thyroidectomy and central neck dissection. None of the 11 patients had nodal extension. All 11 patients are biochemically cured. It was concluded that routine measurement of basal serum CT in those with nodular thyroid disease allows early, preoperative diagnosis of subclinical SMTC and improves the results of surgery.