Impact of chronic lymphocytic thyroiditis on the prognosis of differentiated thyroid cancer

Full text: The association of chronic lymphocytic thyroiditis (CLT) and differentiated thyroid cancer, and its prognosis significance remain controversial. We investigate the prognosis impact of this association by reviewing our series of patients being followed for differentiated thyroid cancer (DTC) at the department of nuclear medicine of Sahloul. Among the 350 patients followed in our department, 30 (8.5%) had histologically proved CLT, with infiltration of the non- tumoral thyroid tissue. A second group of 60 patients (without evidence of lymphocytic infiltration) was selected randomly and used as controls. The median of follow-up for these two groups was 4 years. The frequency of papillary thyroid cancer was significantly higher in the group with CTL (90% vs 74%; p=0.05). The larger diameter of the tumor didn't differ significantly (p= 0.36) between the group with TLC (mean=2.7; SD=1.98) and the control group 3.08 (SD=1.66). There was also no significant difference in capsular infiltration (37% vs 36%; p=0.96), nodal metastases (47% vs 43%; p=0.74), multicentric tumors (37% vs 38%; p=0.99) and bilateral tumors (20% vs 22%; p=0.9). At initial presentation, distant metastases were less frequent in patients with coexisting CLT and DTC (3% vs 12%, p<1%). Nevertheless, if we consider only patients with papillary thyroid cancer, the difference was not statistically significant (0% vs 6%; p=0.23). During the follow-up (mean 4 years), there was no significant difference in nodal relapse (20% vs 8% p=0.1), and distant metastasis (6% vs 3%: p=0.45). No death was noted in the first group, and two were observed in the second (patients with follicular thyroid cancer). The most striking result of this study is the total absence of significant impact of CLT on the prognosis of DTC. Our results seem to be on opposite to those of the majority of authors, underlying the complexity of this entity. We think that some factors specific to our population (iodine diet, ethnical factors etc.) may explain this uncommon result. (author)