Riedel's thyroiditis with destruction of thyroid cartilage: A case report.

Riedel's thyroiditis (RT) is a rare IgG4-related disease typically presenting with fibrotic thyroid enlargement and compressive symptoms. However, we herein report an unusual case of probable RT that involved laryngeal invasion and the thyroid cartilage destruction. In this case, a 46-year-old man presented with hoarseness, dysphagia, and a laryngeal mass. Imaging further revealed the thyroid cartilage permeative destruction with communication into the laryngeal lumen, raising suspicion of malignancy. Subsequent surgical exploration showed inflammatory granulation tissue eroding the thyroid cartilage. Histopathological examination demonstrated fibrous hyperplasia with lymphoplasmacytic infiltration, in hotspots approximately 15 IgG4-positive plasma cells per high-power field, and an IgG4/IgG-positive plasma cell ratio of ∼43%. Storiform fibrosis and obliterative phlebitis were absent. These findings confirmed probable RT with inflammatory pseudotumor formation. To our knowledge, this appears to be among the first reported cases of RT causing thyroid cartilage destruction. The mechanism is speculative but may involve chronic vascular compromise or direct inflammatory erosion. Therefore, RT should be considered in the differential diagnosis of atypical laryngeal lesions with cartilage involvement.