USMLE/COMLEX 3 - Hypoparathyroidism & Calcium Imbalances

Here are key facts for USMLE Step 3 & COMLEX-USA Level 3 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. Treatments include activated Vitamin D and calcium supplements, possibly magnesium supplements. 2. Dietary recommendations: high in calcium (green leafy vegetables, legumes, fortified cereals) and low in phosphorous (less meat, soft drinks, and dairy products, which are high in phosphorus). 3. Low parathyroid hormone leads to low levels of calcium and high levels of phosphate. 4. Typical reference blood calcium range is 2.2-2.6 mmol/L (8.6-10.3 mg/dL). 1. Hypoparathyroidism is 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. 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. 4. Cardiovascular effects include prolonged QT interval or heart failure. 5. In response to reduced extracellular calcium concentration, the parathyroid glands secrete parathyroid hormone (PTH). 1. Two key signs of tetany in hypoparathyroidism: Chvostek sign and Trousseau's sign. 2. Chvostek sign: tapping the facial nerve (in the parotid gland/masseter muscle area) produces facial muscle spasms. 3. 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.

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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. Psychiatric: Irritability and confusion. 2. Cardiovascular: Include prolonged QT interval or heart failure. 3. Ocular: Cataracts 1. Disorders that cause excessive bone resorption: Cancers, Paget disease, hyperthyroidism, Familial hypocalciuric hypercalcemia, Vitamin D toxicity. 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 (less meat, soft drinks, and dairy products). 3. If Vitamin D levels are high, parathyroid hormone secretion is inhibited. 4. Prolonged exposure to parathyroid hormone promotes resorption of old bone, releasing calcium and phosphate into extracellular fluid. 5. Parathyroid hormone increases calcium reabsorption in the distal convoluted tubule of the nephrons. 1. 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. 2. This is very rare.

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Below is information not explicitly contained within the tutorial but important for USMLE & COMLEX 3. 1. Hypercalcemic crisis: aggressive IV hydration, calcitonin, bisphosphonates, hemodialysis in severe cases 2. Symptomatic hypocalcemia: IV calcium gluconate, correction of underlying magnesium deficiency if present 3. Recognition and management of calcium disorders in critically ill patients 1. Monitoring parameters for chronic hypoparathyroidism therapy 2. Titration strategies for vitamin D and calcium supplementation 3. Management of complications: kidney stones, hypercalciuria, nephrocalcinosis 4. Recombinant PTH therapy for refractory cases 1. Geriatric considerations: altered calcium metabolism, polypharmacy interactions 2. Pregnancy and lactation: adaptive changes in calcium homeostasis, management modifications 3. Chronic kidney disease: secondary hyperparathyroidism, calcimimetic agents, phosphate binders 4. Post-bariatric surgery: altered calcium absorption, supplementation requirements 1. Calcimimetics and calcilytics: modulation of calcium-sensing receptor (CaSR) 2. PTH analogs: treatment options for refractory hypoparathyroidism 3. New approaches to surgical management of parathyroid disorders 4. Monitoring technologies for long-term calcium management