USMLE/COMLEX 2 - Hypoparathyroidism & Calcium Imbalances

Here are key facts for USMLE Step 2 & COMLEX-USA Level 2 from the Parathyroid Hormone & Calcium Homeostasis tutorial, as well as points of interest at the end of this document that are not directly addressed in this tutorial but should help you prepare for the boards. See the tutorial notes for further details and relevant links.

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1. Low parathyroid hormone leads to low levels of calcium and high levels of phosphate. 2. Neuromuscular effects: Muscle weakness, Paresthesia (tingling or burning, especially in the feet, hands, and around the mouth), Cramping, Tetany. 3. Laryngospasms, bronchospasms, and stridor are also associated with hypoparathyroidism. 4. Two key signs of tetany in hypoparathyroidism: Chvostek sign and Trousseau's sign. 5. Chvostek sign: tapping the facial nerve (in the parotid gland/masseter muscle area) produces facial muscle spasms. 6. Trousseau's sign: carpopedal spasm seen after a few minutes of wearing an inflated blood pressure cuff (20 mmHg above systolic pressure). In the spasm, the patient will have flexed wrist, thumb, and metacarpophalangeal but hyperextended fingers. 1. Most often the result of surgical removal or damage to the parathyroid glands. 2. Other causes include autoimmune destruction (i.e., Autoimmune polyglandular syndrome type 1), congenital lack of functioning parathyroid glands, and very low magnesium levels. 3. Typical reference blood calcium range is 2.2-2.6 mmol/L (8.6-10.3 mg/dL). 4. Pseudohypoparathyroidism: Patients present with signs and symptoms associated with hypoparathyroidism but normal or elevated levels of parathyroid hormone – these patients have hormone resistance in the target organs. 1. Activated Vitamin D and calcium supplements, possibly magnesium supplements. 2. Patients are often recommended diets high in calcium (consume more green leafy vegetables, legumes, fortified cereals) and low in phosphorous (so, consume less meat, soft drinks, and dairy products, which are high in phosphorus).

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1. Muscle weakness 2. Paresthesia (tingling or burning, especially in the feet, hands, and around the mouth) 3. Cramping 4. Tetany 5. Laryngospasms, bronchospasms, and stridor 1. Irritability and confusion. 1. Include prolonged QT interval or heart failure. 1. Cataracts 1. Chvostek sign: tapping the facial nerve (in the parotid gland/masseter muscle area) produces facial muscle spasms. 2. Trousseau's sign: carpopedal spasm seen after a few minutes of wearing an inflated blood pressure cuff (20 mmHg above systolic pressure). In the spasm, the patient will have flexed wrist, thumb, and metacarpophalangeal but hyperextended fingers. 1. Disorders that cause excessive bone resorption (and therefore calcium release): Cancers, Paget disease, hyperthyroidism, Familial hypocalciuric hypercalcemia, Vitamin D toxicity, etc. 2. Disorders that cause excessive gastrointestinal calcium absorption: Sarcoidosis, other granulomatous diseases. 3. Drugs that increase extracellular calcium, including lithium and thiazide diuretics. 1. Vitamin D deficiency or resistance (including antiseizure drugs that alter vitamin D metabolism) 2. Pancreatitis 3. Magnesium imbalances 1. Activated Vitamin D and calcium supplements, possibly magnesium supplements. 2. Dietary modifications: high in calcium (green leafy vegetables, legumes, fortified cereals) and low in phosphorous (avoid meat, soft drinks, and dairy products). 3. In response to reduced extracellular calcium concentration, the parathyroid glands secrete parathyroid hormone (PTH). 4. If Vitamin D levels are high, parathyroid hormone secretion is inhibited.

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Below is information not explicitly contained within the tutorial but important for USMLE & COMLEX 2. 1. IV calcium gluconate for symptomatic patients or severe hypocalcemia 2. Cardiac monitoring due to risk of arrhythmias with rapid correction 3. Treatment of underlying causes (e.g., surgical hypoparathyroidism, vitamin D deficiency) 1. Often asymptomatic and discovered incidentally on routine labs 2. Classic symptoms: "stones, bones, abdominal groans, and psychic moans" 3. First-line treatment for symptomatic disease is parathyroidectomy 4. Surgical criteria for asymptomatic patients include age <50, significant hypercalcemia, reduced bone density, kidney stones 1. Pregnancy: physiologic changes in calcium homeostasis; management modifications needed 2. Chronic kidney disease: complex alterations in PTH, vitamin D, calcium, and phosphate 3. Elderly patients: increased prevalence of vitamin D deficiency and osteoporosis 1. Sestamibi scan for localizing parathyroid adenomas 2. Ultrasound as complementary study for surgical planning 3. CT and MRI roles in complicated cases 4. 4D-CT emerging as highly sensitive localization technique