Flow cytometry in the diagnosis of autoimmune-related lymphoproliferative disorder and lymphoma in the head and neck region

Salivary, lacrimal, and thyroid glands are frequent sites of manifestations of autoimmune disorders in the head and neck regions. Sjögren syndrome, Hashimoto’s thyroiditis, sarcoidosis, granulomatosis with polyangiitis, and IgG4-related sialadenitis represent the most important autoimmune disorders with clinical manifestations most commonly involving salivary glands, lacrimal glands, and the thyroid. Pathophysiologically, the prolonged antigen stimulation during reactive autoimmune lymphoproliferative processes increases the risk of developing a clonal, malignant neoplasm (i.e., a lymphoma). Flow cytometry (FC) has been recognized as an important ancillary technique in the diagnosis of lymphoid neoplasms, and it can be used in conjunction with fine needle aspiration (FNA) or excisional biopsy in the evaluation of lymphoproliferative processes. Combining immunophenotyping by FC with cytomorphologic examination improves the sensitivity for lymphoma diagnosis. This overview focuses on the application of FC to detect a spectrum of salivary gland-related extranodal lymphoproliferative processes from reactive processes (follicular hyperplasia, interfollicular plasmacytosis, IgG4-related disease, and graft-versus-host disease) to neoplastic diseases, including extranodal marginal zone lymphoma (MALT lymphoma), plasmacytoma, and diffuse large B-cell lymphoma.