WBR0270
| Author | [[PageAuthor::Gonzalo A. Romero, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Pathology, MainCategory::Pathophysiology, MainCategory::Physiology |
| Sub Category | SubCategory::Endocrine |
| Prompt | [[Prompt::A 46-year-old woman presents to the outpatient clinic for a long history of constipation. She states that her symptoms did not improve despite the use of over-the-counter fiber tablets. Her past medical history is significant for recurrent kidney stones. The patient denies any family history of similar symptoms. Upon review of systems, the patient also reports increased thirst, frequent urination, and easy fatigability. Her temperature is 37.1 °C (98.6 °F), blood pressure is 142/88 mmHg, and heart rate is 70/min. Physical examination in the clinic is unremarkable. Work-up reveals decreased bone mineral density in the distal third of the forearm. Urine work-up is remarkable for hypercalciuria. Which of the following set of serum lab results is most likely present in this patient?
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| Answer A | AnswerA::A |
| Answer A Explanation | AnswerAExp::This represents the normal range of calcium and PTH values in serum; calcium levels vary from 8.5 to 10.2 mg/dL and PTH levels vary from 15-65 pg/mL. PTH increases when the ionized calcium level decreases. |
| Answer B | AnswerB::B |
| Answer B Explanation | [[AnswerBExp::Hypoparathyroidism can be caused by surgical removal of the parathyroids (i.e. thyroid surgery), or due to an autoinmune destruction of the glands. The lab values reveal low PTH and low calcium levels.]] |
| Answer C | AnswerC::C |
| Answer C Explanation | [[AnswerCExp::Secondary hyperparathyroidism is characterized by elevated PTH due to decreased levels of calcium. The most common causes are chronic renal insufficiency (due to impaired vitamin D hydroxylation towards its active form) and intestinal malabsorption of calcium.]] |
| Answer D | AnswerD::D |
| Answer D Explanation | [[AnswerDExp::Primary hyperparathyroidism can be caused by an adenoma, hyperplasia or carcinoma in the parathyroid glands. The increased levels of PTH increase the calcium levels above 10, therefore it corresponds to upper right corner on the graph.]] |
| Answer E | AnswerE::E |
| Answer E Explanation | [[AnswerEExp::This option corresponds to hypercalcemia independent of PTH, for example seen in metastatasis or excess calcium ingestion]] |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Primary hyperparathyroidism is the most common cause of hypercalcemia. The most common cause of primary hyperparathyroidism is a single adenoma, which accounts for more than 80% of cases. Less commonly, primary hyperparathyroidism is caused by hyperplasia of the parathyroid glands or hereditary syndromes, such as multiple endocrine neoplasia (MEN) syndromes types 1 and 2A. Although the diagnosis of primary hyperparathyroidism is usually incidental since the majority of patients remain asymptomatic, manifestations of the disorder are primarily due to hypercalcemia. The classical clinical features of hypercalcemia may be summarized as: Stones, bones, groans, and psychiatric overtones.
Other features may include polyuria and polydypsia, easy fatigability, high blood pressure, insulin resistance, hyperglycemia, and dyslipidemia. Typically, initial laboratory findings of patients with primary hyperparathyroidism reveal hypercalcemia on routine work-up. Total serum calcium level should always be differentiated from free and albumin-bound circulating calcium. Accordingly, calcium levels should be corrected and calculated as follows: Corrected serum calcium (mg/dL) = Measured total calcium (mg/dL) + [0.8 x (4.0 - serum albumin (g/dL)]. Patients with hypercalcemia should undergo testing for serum PTH, which is often elevated or inappropriately normal in patients with primary hyperparathyroidism. The definitive diagnosis of primary hyperparathyroidism cannot be made until other diseases that also cause hypercalcemia and/or elevated serum PTH are excluded, such as thiazide or lithium intake, tertiary hyperparathyroidism due to end-stage renal disease (ESRD), familial hypocalciuric hypercalcemia, and PTHrp-secreting malignancies. Of note, PTH and PTHrp are measured separately during laboratory work-up, and patients with PTHrp-secreting tumors usually have low PTH and elevated PTHrp levels). Patients with primary hyperparathyroidism usually have decreased 25-hydroxyvitamin D levels due to the increased conversion to 1,25-dihydroxyvitamin D. Urinary creatinine and calcium levels should be measured to differentiate primary hyperparathyroidism from familial hypocalciuric hypercalcemia (mutation in calcium-sensing receptor gene). In patients with primary hyperparathyroidism, the urinary calcium:creatinine clearance ratio is typically > 0.01. Parathyroidectomy is often required to treat patients with symptomatic disease. Physiologically, PTH has many functions:
 Educational Objective: Hyperparathyroidism is frequently caused by a hyperfunctioning adenoma in a parathyroid gland. PTH increases calcium and phosphorus serum levels |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::PTH, WBRKeyword::Primary hyperparathyroidism, WBRKeyword::Hyperparathyroidism, WBRKeyword::Hypercalcemia, WBRKeyword::Constipation, WBRKeyword::Polyuria, WBRKeyword::Polydypsia, WBRKeyword::Calcium, WBRKeyword::Phosphate, WBRKeyword::Vitamin D, WBRKeyword::Kidney stones, WBRKeyword::Nephroplithiasis, WBRKeyword::Hypercalciuria |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |