Incidental versus clinical diagnosis of papillary thyroid microcarcinoma. Long-term prognosis

The incidence of papillary thyroid microcarcinoma (PTMC) has increased in recent years, especially in patients operated on for presumably benign thyroid disease. The aim of this study was to analyze the differences between PTMC incidentally diagnosed and PTMC clinically diagnosed, as well as its long-term prognosis.

The study population consisted of patients with a histological diagnosis of PTMC. Patients with previous thyroid surgery, other synchronous thyroid or extrathyroid malignancies and an ectopic location of PTMC were excluded. Two groups were compared: patients with PTMC incidentally diagnosed (group 1) and patients with PTMC clinically diagnosed (group 2). A multivariate analysis of differentiating factors was performed.

PTMC clinically diagnosed had a high frequency of hypothyroidism (4.6% vs. 18.9%; P=.004), extrathyroidal extension (5.7% vs. 17.6%; P=.018), metastatic lymph nodes (1.1% vs. 18.9%; P<.001) and lymphocytic thyroiditis (5.7% vs. 27%; P<.001). In the multivariate analysis, metastatic lymph nodes (OR: 22.011, IC 95%: 2.621-184.829; P=.004) and lymphocytic thyroiditis (OR: 4.949; IC 95%: 1.602-15.288; P=.005) were associated with the clinical diagnosis of PTMC. During a mean follow-up of 119.8±65.1 months, one recurrence was detected in group 2 (0% vs. 1,4%; P=.460). No patient died due to the disease.

PTMC clinically diagnosed, although it has more aggressive histopathological characteristics (extrathyroidal extension and metastatic lymph nodes), presents a long-term prognosis similar to the PTMC incidentally diagnosed. The presence of metastatic lymph nodes and lymphocytic thyroiditis were independent factors associated with PTMC clinically diagnosed.