SUN-363 - Diffuse Sclerosing Papillary Thyroid Carcinoma Presenting as Biochemical and Clinical Hyperthyroidism

Diffuse sclerosing papillary thyroid carcinoma (DS-PTC) is a rare and aggressive variant of papillary thyroid cancer, typically characterized by extensive fibrosis, lymphocytic infiltration, psammoma bodies, and diffuse involvement of one or both thyroid lobes. It most commonly presents in younger individuals and is often associated with cervical lymph node metastasis at diagnosis. Hyperthyroidism is an uncommon clinical manifestation of DS-PTC, as most thyroid malignancies are functionally inactive. We report a case of DS-PTC presenting with biochemical and clinical hyperthyroidism, highlighting the diagnostic challenges and underlying pathophysiological considerations.

A 44-year-old woman presented with symptoms of thyrotoxicosis, including weight loss, palpitations, and heat intolerance. Laboratory evaluation revealed suppressed thyroid-stimulating hormone (TSH) and elevated free thyroxine (fT4). Thyroid ultrasonography demonstrated a diffusely enlarged gland with heterogeneous echotexture and scattered microcalcifications, without a dominant nodule. Radioiodine uptake was diffusely increased, initially suggestive of autoimmune hyperthyroidism. However, fine-needle aspiration cytology raised suspicion for malignancy, and subsequent histopathological examination following total thyroidectomy confirmed DS-PTC.

The coexistence of hyperthyroidism and DS-PTC is rare and may be attributed to tumor-associated stimulation of thyroid hormone production or concurrent autoimmune thyroid disease. This case underscores the importance of maintaining a high index of suspicion for malignancy in atypical presentations of hyperthyroidism, particularly when imaging findings are incongruent with classic benign etiologies. Early recognition and appropriate surgical management are critical due to the aggressive nature of DS-PTC and its propensity for regional spread.

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