A 46-year-old woman presents to her primary care doctor to request a referral to ophthalmology. Her vision has been steadily declining over the past 2 years and she thinks she needs a prescription for glasses. She further complains that her lips and feet feel numb. Her medical history is notable for medullary thyroid cancer status post total thyroidectomy. Her periods are regular. She enjoys a diverse diet and takes levothyroxine. Her blood pressure is 110/70 mmHg, pulse is 80/min, and respirations are 12/min. She is alert and oriented. Her pupils are equal, round, and reactive to light, but appear opacified. Extraocular movements are intact, albeit slow. Her visual acuity is decreased bilaterally. The remainder of her physical exam is unremarkable. Her basic metabolic panel is shown below: Na+: 139 mEq/L Cl-: 100 mEq/L K+: 4.9 mEq/L HCO3-: 25 mEq/L BUN: 10 mg/dL Glucose: 110 mg/dL Creatinine: 0.8 mg/dL Thyroid-stimulating hormone: 1.5 µU/mL Ca2+: 7.0 mEq/L Phosphorus: 6.5 mEq/L Albumin: 3.6 mg/dL The patient's ECG is shown in Figure A. What is the most likely cause of this presentation?
Iatrogenic hypoparathyroidism
Somatization
Multiple endocrine neoplasia
Hyperkalemia
Iatrogenic hypoparathyroidism
This patient who presents with cataracts and a prolonged QTc interval on ECG most likely has symptomatic hypocalcemia secondary to the surgical removal of all of her parathyroid glands (iatrogenic hypoparathyroidism).

Thyroid surgery may mandate the removal of parathyroid glands if there is evidence of malignant invasion. One parathyroid gland is enough to maintain eucalcemia, but accidental/intentional removal of all the glands is possible. Less common causes are autoimmune parathyroid destruction or parathyroid infiltration by disorders like sarcoidosis or Wilson disease. Many patients are asymptomatic, but chronic hypocalcemia is associated with increased phosphate levels, prolonged QT interval, Parkinsonian signs, cataracts, and cognitive impairment. Severe, acute hypocalcemia can present with tetany, papilledema, and seizures. Treatment is with calcium and parathyroid hormone replacement.

Clarke et al. review the evidence regarding the diagnosis and etiologies of hypoparathyroidism. They discuss how the most common cause is post-surgical. They recommend obtaining genetic testing in cases where the etiology is unclear.

Figure/Illustration A shows an ECG with a prolonged QTc interval at approximately 500 msec (blue circle).

Incorrect Answers:
Answer A: This patient is mildly hyperkalemic, but her symptoms and signs are not associated with hyperkalemia. Patients with hyperkalemia present with heart palpitations, shortness of breath, chest pain, nausea, or vomiting. ECG will demonstrate peaked T waves.

Answer C: The patient is on levothyroxine with appropriate TSH levels. Hypothyroidism is not associated with QT prolongation. Patients with hypothyroidism will present with cold intolerance, delayed responsiveness, and myxedema coma. Treatment is with increasing the levothyroxine dose.

Answer D: Multiple endocrine neoplasia is associated with medullary thyroid cancer, but this patient has no evidence of additional organ disease. Other signs of multiple endocrine neoplasia include pancreatic tumors, pheochromocytoma, or a Marfanoid habitus. Treatment is with surgical excision of tumors.

Answer E: This patient most likely has a biological reason for her symptoms, so somatization is less likely. Patients with somatizing disorders have psychological distress that manifests as physical symptoms. These patients will not have organic correlates of disease such as abnormal ECG results.

Bullet Summary:
Iatrogenic hyperparathyroidism after the removal of the thyroid gland is the most common cause of hypocalcemia.