Late-Onset Thyroid Hormone Resistance Following Total Thyroidectomy for Papillary Thyroid Cancer.

Thyroid hormone resistance (RTH) is a rare disorder characterized by impaired cellular responsiveness to thyroid hormones, leading to discordant thyroid function tests and varied clinical manifestations. We present the case of a 43-year-old Cuban-American female patient who presented with dizziness, vertigo, repeated falls, and a severe headache following a minor fall. Additional symptoms included nausea, vomiting, photophobia, cold intolerance, generalized body aches, and fatigue. Her medical history was significant for total thyroidectomy for papillary thyroid cancer, multiple sclerosis (MS), pituitary macroadenoma, Cushing's disease, and polycystic ovary syndrome (PCOS). Post-thyroidectomy, she remained on high-dose levothyroxine (400-750 mcg daily). However, laboratory tests showed persistently elevated thyroid-stimulating hormone (TSH) levels, hence raising suspicion for RTH. This case highlights the challenges of diagnosing and managing RTH, a rare endocrine disorder often resulting from mutations in the thyroid hormone receptor-beta (THB) gene. RTH is characterized by inappropriately normal or elevated TSH despite high thyroid hormone levels, reflecting tissue-level resistance. This case underscores the complexities of identifying RTH in the setting of multiple comorbidities and a history of thyroidectomy. It also emphasizes the need for clinician awareness of atypical presentations of RTH, particularly in patients with extensive endocrine and systemic histories.