A 55-year-old man presents to the emergency department complaining of progressive muscle cramps and tingling sensations in his hands and around his mouth that began several hours ago. He also reports a noticeable decline in his vision over the past few years, which he attributed to aging. His medical history includes a total thyroidectomy performed five years prior for medullary thyroid carcinoma, for which he has been consistently taking levothyroxine. He denies recent trauma or changes in medication. On examination, his blood pressure is 120/80 mmHg, pulse 72/min, respirations 16/min, and temperature 37.0°C. He appears anxious and demonstrates carpopedal spasm upon inflation of a blood pressure cuff (Trousseau's sign) and facial muscle twitching upon tapping the facial nerve (Chvostek's sign). Ophthalmic examination reveals bilateral lenticular opacities. The cardiac auscultation is regular without murmurs. Neurological exam shows intact motor strength but reduced sensation to light touch in a stocking-glove distribution. The patient's ECG reveals a QTc interval of 500 msec. What is the most likely underlying diagnosis given this presentation, and what is the most critical immediate therapeutic intervention?

A 60-year-old woman presents to her outpatient endocrinology clinic for routine follow-up regarding her chronic hypoparathyroidism. She underwent a total thyroidectomy for follicular thyroid carcinoma 3 years ago, which was complicated by persistent hypoparathyroidism. She has been stable on levothyroxine 100 mcg daily, calcium carbonate 1000 mg three times daily, and calcitriol 0.5 mcg twice daily. Despite adherence to her regimen, she reports new, mild, intermittent perioral numbness and occasional muscle twitches over the past month. Physical examination reveals stable vital signs, no Chvostek or Trousseau signs elicited, and an otherwise unremarkable neurological assessment. Her recent lab results show a serum calcium of 2.15 mmol/L (normal: 2.1-2.5 mmol/L), serum magnesium of 0.85 mmol/L (normal: 0.7-1.0 mmol/L), and 24-hour urine calcium excretion of 5.5 mmol/24h (normal: 2.5-7.5 mmol/24h). Her serum creatinine is 70 mcmol/L (normal: 50-100 mcmol/L), and 25-hydroxyvitamin D level is 70 nmol/L (normal: 50-125 nmol/L). Her parathyroid hormone (PTH) level is undetectable (<1 pg/mL) (normal: 10-65 pg/mL). However, her latest serum phosphorus level is 1.6 mmol/L (normal: 0.8-1.45 mmol/L). Considering her current symptoms and lab findings, what is the most crucial additional parameter to monitor in this patient's hypoparathyroidism management, and what immediate therapeutic adjustment should be considered?

A 32-year-old man presents to the emergency department complaining of acute onset muscle spasms, tingling sensations in his fingertips and around his mouth, and a feeling of "pins and needles" in his lower extremities. He reports a history of Graves' disease and underwent a total thyroidectomy five days ago. He is currently on levothyroxine replacement therapy. On examination, Chvostek's sign is positive, and Trousseau's sign can be elicited. Given these findings, what is the most likely diagnosis and the appropriate initial management strategy?