Prevalence of thyroiditis and immunohistochemistry study searching for a morphologic consensus in morphology of autoimmune thyroiditis in a 4613 autopsies series

We sought to verify the prevalence of lymphocytic thyroiditis (LT) and Hashimoto's thyroiditis (HT) in autopsy materials. Cases examined between 2003 and 2007 at the Department of Pathology of Faculty of Medicine of São Paulo University were studied. Immunohistochemical analyses were conducted in selected cases to characterize the type of infiltrating mononuclear cells; in addition, we evaluated the frequency of apoptosis by TUNEL assay technique and caspase-3 immunostaining. Significant increase in overall thyroiditis frequency was observed in the present series when compared with the previous report (2.2978% vs. 0.0392%). Thyroiditis was more prevalent among older people. Selected cases of LT and HT (5 cases each) had their infiltrating lymphocytes characterized by immunohistochemical analyses. Both LT and HT showed similar immunostaining patterns for CD4, CD8, CD68, thus supporting a common pathophysiology mechanism and indicating that LT and HT should be considered different presentations of a same condition, that is, autoimmune thyroiditis. Moreover, apoptosis markers strongly evidenced that apoptosis was present in all studied cases. Our results demonstrated an impressive increase in the prevalence of thyroiditis during recent years and our data support that the terminology of autoimmune thyroiditis should be used to designate both LT and HT. This classification would facilitate comparison of prevalence data from different series and studies.