A 58-year-old woman presents with difficulty in swallowing. A thorough workup by a gastroenterologist fails to reveal any primary esophageal disease. The woman is referred to an endocrinologist for evaluation of her thyroid. The endocrinologist suspects Riedel thyroiditis. Which of the following findings on physical examination would best help confirm the diagnosis?

Riedel thyroiditis, also called ligneous (rocklike) stroma, is a rare form of chronic thyroiditis characterized microscopically by a marked fibrous reaction that destroys most or all of the thyroid gland and may involve adjacent structures. The etiology is unknown. Clinically, this disease tends to affect middle-aged and older, mostly female patients and causes the thyroid to have a firm "woody" texture. It may be clinically mistaken for a neck malignancy and can cause symptoms of stridor, dyspnea, dysphasia, laryngeal nerve paralysis, or hypothyroidism. Eyeball protrusion suggests the hypehyroidism of Graves disease. A massive, soft thyroid gland suggests multinodular goiter. A painful and tender thyroid suggests subacute granulomatous (de Quervain) thyroiditis. Ref: Lal G., Clark O.H. (2010). Chapter 38. Thyroid, Parathyroid, and Adrenal. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.