Sonographic studies have revealed that IgG4-thyroiditis is significantly associated with diffuse low echogenicity, whereas non-IgG4 thyroiditis seems to be associated with diffuse coarse echogenicity.

Several sonographic patterns have been reported in HT [33–35] and studies aimed at the identification of an association between sonographic findings and the degree of thyroid function impairment have been conducted [36, 37]. Data have been reported demonstrating that patients with remarkable hypoechogenicity of the thyroid gland (i.e., the echogenicity of the thyroid was almost equal to or less than that of the adjacent muscles) had abnormally low T4 and abnormally high TSH more frequently than patients with coarse echogenicity. Thus, the observation that IgG4-thyroiditis is significantly associated with diffuse low echogenicity is likely to suggest that this form is more frequently associated with hypothyroidism and follicular degeneration [2]. See Fig. 7.1 for representative ultrasound images of normal thyroid and chronic Hashimoto’s thyroiditis.

The potential association between IgG4-RD and thyroid disease represents a matter of increasing interest. There is no doubt that larger studies are needed in order to better define this relationship. Identifying subsets of patients with IgG4-thyroiditis, based either on tissue or serum findings, could be important for several clinical aspects. The more rapid progression towards surgery due to thyroid gland enlargement in the IgG4-thyroiditis subgroup could lead investigators to explore whether this subset warrants immunosuppressive therapy, and whether immunosuppression may halt disease progression. In addition, a more rapid loss of thyroid function of IgG4-thyroiditis patients may lead to earlier interventions in treating hypothyroidism. Finally, from an investigative perspective, IgG4-related and -unrelated forms of thyroiditis may recognize different proteins as target antigens of autoantibody production, and may reveal different immunopathogenic patterns leading to thyroid inflammation and fibrosis.