An infiltrate of IgG4-positive lymphoplasmacytic cells can occur in thyroiditis.
General features:
(1) The histologic appearance may be classified as Riedel's thyroiditis or a variant of Hashimoto's thyroiditis.
(2) Inflammation may be limited to the thyroid or part of a systemic IgG4-related disease.
(3) diffuse sonographic echogenicity of the thyroid gland.
(4) elevated serum concentration of IgG4
(5) elevated serum thyroid autoantibodies
Histologic features:
(1) a dense infiltrate of IgG4-positive lymphocytes and plasma cells (see below).
(2) fibrosis vs sclerosis vs stromal fibrosis, which may be mild and which may be interfollicular
Criteria of Li et al (2009):
(1) > 20 IgG4 positive plasma cells per high power field
(2) IgG4 to IgG ratio > 30%
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Specialty: Endocrinology, Immunology/Rheumatology
