Vitamin D deficiency and rickets — MCQs

10 questions

A 70-year-old woman presents to the office for a yearly physical. She states she has recently started experiencing pain in her legs and her back. Last year, she experienced a fracture of her left arm while trying to lift groceries. The patient states that she does not consume any dairy and does not go outside often because of the pain in her legs and back. Of note, she takes carbamazepine for seizures. On exam, her vitals are within normal limits. You suspect the patient might have osteomalacia. Testing for which of the following is the next best step to confirm your suspicion?

A 57-year-old man presents the urgent care clinic with a one-week history of diffuse bone pain and generalized weakness. He was diagnosed with end-stage renal disease 6 months ago and is currently on dialysis. His wife, who is accompanying him today, adds that he is not compliant with his medicines. He has been diabetic for the last 10 years and hypertensive for the last 7 years. He has smoked 4–5 cigarettes per day for 30 years but does not drink alcohol. His family history is insignificant. On examination, the patient has a waddling gait. Hypotonia of all the limbs is evident on neurologic examination. Diffuse bone tenderness is remarkable. X-ray of his legs reveal osteopenia and osseous resorption. The final step of activation of the deficient vitamin in this patient occurs by which of the following enzymes?

A 67-year-old Caucasian female presents to her primary care physician after a screening DEXA scan reveals a T-score of -3.0. Laboratory work-up reveals normal serum calcium, phosphate, vitamin D, and PTH levels. She smokes 1-2 cigarettes per day. Which of the following measures would have reduced this patient's risk of developing osteoporosis?

A 6-month-old girl is brought to the physician for a well-child examination. She was born at 37 weeks' gestation. Pregnancy and the neonatal period were uncomplicated. The infant was exclusively breastfed and received vitamin D supplementation. She can sit unsupported and can transfer objects from one hand to the other. She babbles and is uncomfortable around strangers. She is at 40th percentile for length and at 35th percentile for weight. Vital signs are within normal limits. Physical examination shows no abnormalities. In addition to continuing breastfeeding, which of the following is the most appropriate recommendation at this time?

A 28-year-old gravida 1 para 1 woman is being seen in the hospital for breast tenderness. She reports that both breasts are swollen and tender. She is also having difficulty getting her newborn to latch. The patient gave birth 4 days ago by uncomplicated vaginal delivery. During her pregnancy, the patient developed gestational diabetes but was otherwise healthy. She took folate and insulin. She attended all her pre-natal appointments. Upon examination, the patient has a low grade fever, but all other vital signs are stable. Bilateral breasts appear engorged and are tender to palpation. There is no erythema, warmth, or induration. A lactation nurse is brought in to assist the patient and her newborn with more effective breastfeeding positions. The patient says a neighbor told her that breastmilk actually lacks in nutrients, and she asks what the best option is for the health of her newborn. Which of the following components is breastmilk a poor source of?

A 3-month-old African American boy presents to his pediatrician’s office for his routine well visit. He was born full-term from an uncomplicated vaginal delivery. He is exclusively breastfeeding and not receiving any medications or supplements. Today, his parents report no issues or concerns with their child. He is lifting his head for brief periods and smiling. He has received only 2 hepatitis B vaccines. Which of the following is the correct advice for this patient’s parents?

A 35-year-old female presents to her primary care physician complaining of right upper quadrant pain over the last 6 months. Pain is worst after eating and feels like intermittent squeezing. She also admits to lighter colored stools and a feeling of itchiness on her skin. Physical exam demonstrates a positive Murphy's sign. The vitamin level least likely to be affected by this condition is associated with which of the following deficiency syndromes?

A child presents with rachitic changes in the limbs that are not responding to Vitamin D supplementation. Investigations reveal the following results: - Calcium: $9.5 \mathrm{mg} / \mathrm{dl}$ - Phosphorus: $1.6 \mathrm{mg} / \mathrm{dl}$ - Alkaline phosphatase (ALP): 814 IU - Serum PTH: $24.2 \mathrm{pg} / \mathrm{ml}$ - Serum electrolytes, creatinine, and blood gases: Normal. What is the most likely diagnosis?

A 65-year-old female with chronic renal failure presents with recent onset of bone pain. Serum analysis reveals decreased levels of calcium and elevated levels of parathyroid hormone. One of the mechanisms driving the elevated PTH is most similar to that seen in:

Q10

A 68-year-old man comes to the physician because of fatigue and muscle cramps for the past 4 weeks. He has also noticed several episodes of tingling in both hands. He has not had fever or nausea. He has had a chronic cough for 10 years. He has chronic bronchitis, hypertension, and osteoarthritis of both knees. His father died from lung cancer. Current medications include salbutamol, ibuprofen, and ramipril. He has smoked 1 pack of cigarettes daily for 45 years. He is 175 cm (5 ft 9 in) tall and weighs 68 kg (163 lb); BMI is 22 kg/m2. His temperature is 36.7°C (98°F), pulse is 60/min, and blood pressure is 115/76 mm Hg. While measuring the patient's blood pressure, the physician observes carpopedal spasm. Cardiopulmonary examination shows no abnormalities. His hematocrit is 41%, leukocyte count is 5,800/mm3, and platelet count is 195,000/mm3. Serum alkaline phosphatase activity is 55 U/L. An ECG shows sinus rhythm with a prolonged QT interval. Which of the following is the most likely underlying cause of this patient's symptoms?

Vitamin D deficiency and rickets US Medical PG Practice Questions and MCQs

Question 1: A 70-year-old woman presents to the office for a yearly physical. She states she has recently started experiencing pain in her legs and her back. Last year, she experienced a fracture of her left arm while trying to lift groceries. The patient states that she does not consume any dairy and does not go outside often because of the pain in her legs and back. Of note, she takes carbamazepine for seizures. On exam, her vitals are within normal limits. You suspect the patient might have osteomalacia. Testing for which of the following is the next best step to confirm your suspicion?

A. Vitamin D2 (ergocalciferol)
B. 25-hydroxyvitamin D (Correct Answer)
C. Pre-vitamin D3
D. 1,25-hydroxyvitamin D
E. 7-dehydrocholesterol

Explanation: ***25-hydroxyvitamin D*** - This is the **best initial test** for evaluating vitamin D deficiency, which leads to **osteomalacia**. - It reflects the circulating levels of vitamin D and is the **most accurate indicator** of the body's vitamin D stores. *Vitamin D2 (ergocalciferol)* - While D2 is a form of vitamin D, measuring only D2 levels is **not sufficient** to assess overall vitamin D status. - The standard test measures total circulating vitamin D, which includes both D2 and D3, but specifically **25-hydroxyvitamin D** reflects the active usable form. *Pre-vitamin D3* - **Pre-vitamin D3** is a precursor molecule formed in the skin from 7-dehydrocholesterol upon UV exposure, and it rapidly isomerizes to vitamin D3. - It is **not a stable measurable form** in the blood for assessing vitamin D status or diagnosing osteomalacia. *1,25-hydroxyvitamin D* - This is the **active hormonal form of vitamin D**, primarily regulated by parathyroid hormone (PTH) and kidney function. - Levels can be normal or even elevated in early vitamin D deficiency due to increased PTH, making it **less reliable** for initial assessment of deficiency. *7-dehydrocholesterol* - **7-dehydrocholesterol** is a precursor molecule in the skin that is converted to pre-vitamin D3 by UV radiation. - Measuring this precursor is **not clinically significant** for diagnosing osteomalacia or assessing vitamin D deficiency.

Question 2: A 57-year-old man presents the urgent care clinic with a one-week history of diffuse bone pain and generalized weakness. He was diagnosed with end-stage renal disease 6 months ago and is currently on dialysis. His wife, who is accompanying him today, adds that he is not compliant with his medicines. He has been diabetic for the last 10 years and hypertensive for the last 7 years. He has smoked 4–5 cigarettes per day for 30 years but does not drink alcohol. His family history is insignificant. On examination, the patient has a waddling gait. Hypotonia of all the limbs is evident on neurologic examination. Diffuse bone tenderness is remarkable. X-ray of his legs reveal osteopenia and osseous resorption. The final step of activation of the deficient vitamin in this patient occurs by which of the following enzymes?

A. α-1-antitrypsin
B. 24,25 hydroxylase
C. α-Glucosidase
D. 7-α-hydroxylase
E. 1-α-hydroxylase (Correct Answer)

Explanation: ***1-α-hydroxylase*** - The patient's symptoms (diffuse bone pain, generalized weakness, waddling gait, hypotonia, osteopenia, and osseous resorption) in the context of **end-stage renal disease (ESRD)** and non-compliance strongly suggest **renal osteodystrophy**, specifically **osteomalacia** due to impaired vitamin D activation. - In ESRD, the kidneys are unable to produce sufficient amounts of **calcitriol (1,25-dihydroxyvitamin D)**, which is the active form of vitamin D. The enzyme responsible for the final activation step, converting 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, is **1-α-hydroxylase**, primarily located in the renal proximal tubules. *α-1-antitrypsin* - This enzyme is a **serine protease inhibitor** primarily involved in protecting tissues from damage by proteases, especially in the lungs. - Deficiency is associated with conditions like **emphysema** and **liver disease**, not directly with bone metabolism or vitamin D activation. *24,25 hydroxylase* - The enzyme **24-hydroxylase** inactivates calcitriol and its precursor by converting them into inert forms. - Its activity would lead to reduced active vitamin D, mimicking a deficiency, but it is not the enzyme responsible for the **final activation step** of vitamin D. *α-Glucosidase* - This enzyme is crucial for the digestion of **carbohydrates** in the small intestine, breaking down complex sugars into glucose. - Deficiencies are associated with conditions like **Pompe disease (glycogen storage disease type II)**, which primarily affects muscle and liver, not vitamin D metabolism. *7-α-hydroxylase* - **Cholesterol 7-α-hydroxylase (CYP7A1)** is a rate-limiting enzyme in the **bile acid synthesis pathway** in the liver. - It plays no direct role in the activation of vitamin D; its function is related to cholesterol metabolism and bile production.

Question 3: A 67-year-old Caucasian female presents to her primary care physician after a screening DEXA scan reveals a T-score of -3.0. Laboratory work-up reveals normal serum calcium, phosphate, vitamin D, and PTH levels. She smokes 1-2 cigarettes per day. Which of the following measures would have reduced this patient's risk of developing osteoporosis?

A. Weight loss
B. Reduced physical activity to decrease the chance of a fall
C. Initiating a swimming exercise program three days per week
D. Calcium and vitamin D supplementation
E. Smoking cessation (Correct Answer)

Explanation: ***Smoking cessation*** - **Smoking** is a well-established, modifiable risk factor for osteoporosis that directly impairs bone metabolism - Cigarette smoking **decreases osteoblast activity**, increases **bone resorption**, and reduces intestinal calcium absorption - This patient is **actively smoking 1-2 cigarettes per day**, making cessation the most relevant preventive measure for her specific situation - **Smoking cessation** would have directly addressed a harmful exposure that contributed to her bone loss *Calcium and vitamin D supplementation* - While important for bone health, this patient's laboratory work-up shows **normal serum calcium and vitamin D levels** - Supplementation beyond adequate levels has **limited additional benefit** for osteoporosis prevention in patients with normal baseline values - Supplementation is most beneficial in patients with documented **deficiency** or inadequate dietary intake *Weight loss* - **Weight loss** and being underweight are actually **risk factors for osteoporosis** - Lower body weight reduces mechanical loading on bones, which is necessary for maintaining bone density - Weight-bearing stress stimulates bone formation through mechanotransduction *Initiating a swimming exercise program three days per week* - While **swimming** is excellent for cardiovascular fitness and overall health, it is **not a weight-bearing exercise** - Osteoporosis prevention requires **weight-bearing or resistance exercises** such as walking, jogging, dancing, or strength training - These activities provide the mechanical stress needed to stimulate bone formation *Reduced physical activity to decrease the chance of a fall* - **Reducing physical activity** accelerates bone loss due to decreased mechanical loading - While fall prevention is important in osteoporosis management, it should focus on **environmental modifications** and **balance training**, not activity reduction - Maintaining appropriate physical activity is essential for preserving bone density

Question 4: A 6-month-old girl is brought to the physician for a well-child examination. She was born at 37 weeks' gestation. Pregnancy and the neonatal period were uncomplicated. The infant was exclusively breastfed and received vitamin D supplementation. She can sit unsupported and can transfer objects from one hand to the other. She babbles and is uncomfortable around strangers. She is at 40th percentile for length and at 35th percentile for weight. Vital signs are within normal limits. Physical examination shows no abnormalities. In addition to continuing breastfeeding, which of the following is the most appropriate recommendation at this time?

A. Continue vitamin D
B. Introduce solid foods
C. Introduce solid foods and add vitamin C
D. Introduce solid foods and cow milk
E. Introduce solid foods and continue vitamin D (Correct Answer)

Explanation: ***Introduce solid foods and continue vitamin D*** - At **6 months of age**, infants typically show developmental readiness for **solid foods**, such as the ability to sit unsupported and transfer objects, while **breastfeeding** continues to be important. - **Vitamin D supplementation** should continue as it is crucial for bone health and is not adequately supplied by breast milk or early solid foods alone. *Continue vitamin D* - While vitamin D supplementation is important, this option **misses the crucial developmental milestone** of introducing solid foods at 6 months. - At this age, infants' **iron stores** begin to dwindle, and solid foods are needed to provide essential nutrients not sufficiently met by breast milk alone. *Introduce solid foods* - This option correctly identifies the need to introduce solid foods but **fails to mention the continued importance of vitamin D supplementation**. - Breastfed infants require continued **vitamin D supplementation** to prevent **rickets**, as breast milk does not contain sufficient amounts. *Introduce solid foods and add vitamin C* - While **vitamin C** is important, the primary focus at 6 months should be on **iron-rich solid foods** and continued **vitamin D supplementation**. - Breast milk contains adequate vitamin C, and introducing diverse solid foods typically provides enough, making dedicated vitamin C supplementation usually unnecessary unless a deficiency is identified. *Introduce solid food and cow milk* - **Cow's milk** should **not be introduced** as a primary drink before **12 months of age** because it can cause **gastrointestinal bleeding**, **iron-deficiency anemia**, and is difficult for infants to digest. - Introducing cow's milk too early can also interfere with the absorption of essential nutrients from breast milk or formula.

Question 5: A 28-year-old gravida 1 para 1 woman is being seen in the hospital for breast tenderness. She reports that both breasts are swollen and tender. She is also having difficulty getting her newborn to latch. The patient gave birth 4 days ago by uncomplicated vaginal delivery. During her pregnancy, the patient developed gestational diabetes but was otherwise healthy. She took folate and insulin. She attended all her pre-natal appointments. Upon examination, the patient has a low grade fever, but all other vital signs are stable. Bilateral breasts appear engorged and are tender to palpation. There is no erythema, warmth, or induration. A lactation nurse is brought in to assist the patient and her newborn with more effective breastfeeding positions. The patient says a neighbor told her that breastmilk actually lacks in nutrients, and she asks what the best option is for the health of her newborn. Which of the following components is breastmilk a poor source of?

A. Whey protein
B. Vitamin D (Correct Answer)
C. Lysozymes
D. Phosphorus
E. Immunoglobulin A

Explanation: ***Vitamin D*** - **Breast milk** is naturally a **poor source of vitamin D**, making supplementation necessary for breastfed infants to prevent **rickets** and ensure adequate bone development. - While small amounts of vitamin D are present, they are often insufficient to meet the infant's requirements, especially if maternal vitamin D levels are also low. *Whey protein* - **Whey protein** is a major component of breast milk, contributing to its digestibility and providing essential **amino acids** for infant growth. - It is specifically rich in **alpha-lactalbumin**, which has both nutritional and antimicrobial properties. *Lysozymes* - **Lysozymes** are abundant in breast milk and play a crucial role in the infant's innate **immune defense** by breaking down bacterial cell walls. - These enzymes help protect against gastrointestinal infections and contribute to the establishment of healthy gut flora. *Phosphorus* - **Phosphorus** is an essential mineral found in sufficient quantities in **breast milk**, crucial for **bone mineralization**, energy metabolism, and cell function. - Its concentration is carefully regulated to meet the needs of the growing infant without overloading immature kidneys. *Immunoglobulin A* - **Secretory IgA (sIgA)** is the predominant **immunoglobulin** in breast milk, providing passive immunity by coating the infant's intestinal tract and preventing pathogen attachment. - It is crucial for protecting the infant from various infections, especially those affecting the gastrointestinal and respiratory systems.

Question 6: A 3-month-old African American boy presents to his pediatrician’s office for his routine well visit. He was born full-term from an uncomplicated vaginal delivery. He is exclusively breastfeeding and not receiving any medications or supplements. Today, his parents report no issues or concerns with their child. He is lifting his head for brief periods and smiling. He has received only 2 hepatitis B vaccines. Which of the following is the correct advice for this patient’s parents?

A. He should be sleeping more.
B. He should have his serum lead level checked to screen for lead intoxication.
C. He should start vitamin D supplementation. (Correct Answer)
D. He should start rice cereal.
E. He needs a 3rd hepatitis B vaccine.

Explanation: ***He should start vitamin D supplementation.*** - **Exclusively breastfed** infants, regardless of maternal vitamin D intake, require **vitamin D supplementation** due to insufficient amounts in breast milk. - The recommended daily dose is **400 IU** starting from the first few days of life, to prevent **rickets** and promote bone health. - **African American infants** have an additional risk factor due to increased skin melanin content, which reduces cutaneous vitamin D synthesis from sunlight exposure. *He should be sleeping more.* - A 3-month-old infant typically sleeps between **14-17 hours per day**, with **waking periods to feed** and interact. - The case description does not indicate any concerns with the child's sleep patterns, and **developmental milestones** like lifting his head and smiling are being met. *He should have his serum lead level checked to screen for lead intoxication.* - **Lead screening** is not routinely recommended for all infants unless specific **risk factors** are present, such as living in an older home with lead paint, or having siblings with elevated lead levels. - There are no reported risk factors for lead exposure in this patient's history. *He should start rice cereal.* - Introduction of solid foods, such as rice cereal, is typically recommended around **6 months of age**, when the infant shows signs of **developmental readiness**. - These signs include **head control**, sitting with support, and showing interest in food. *He needs a 3rd hepatitis B vaccine.* - The **third dose of the hepatitis B vaccine** is typically administered between **6 and 18 months of age**. - At 3 months old, the infant is not yet due for his third dose.

Question 7: A 35-year-old female presents to her primary care physician complaining of right upper quadrant pain over the last 6 months. Pain is worst after eating and feels like intermittent squeezing. She also admits to lighter colored stools and a feeling of itchiness on her skin. Physical exam demonstrates a positive Murphy's sign. The vitamin level least likely to be affected by this condition is associated with which of the following deficiency syndromes?

A. Rickets and osteomalacia
B. Hemolytic anemia
C. Night blindness
D. Increased prothrombin time and easy bleeding
E. Scurvy (Correct Answer)

Explanation: ***Scurvy*** - This condition is likely **cholestasis** due to common bile duct obstruction, given the RUQ pain after eating, light-colored stools, itchiness, and **positive Murphy's sign**. - Cholestasis impairs the absorption of **fat-soluble vitamins** (A, D, E, K), but not **water-soluble vitamins** like vitamin C, which prevents scurvy. *Rickets and osteomalacia* - These conditions are caused by **vitamin D deficiency**, which is a **fat-soluble vitamin**. - Impaired fat absorption in cholestasis would significantly impact vitamin D levels, leading to increased risk of rickets in children and osteomalacia in adults. *Hemolytic anemia* - This can be caused by **vitamin E deficiency**, a **fat-soluble vitamin**. - Cholestasis impairs vitamin E absorption, which can lead to increased red blood cell fragility and hemolytic anemia. *Night blindness* - This is a classic symptom of **vitamin A deficiency**, which is a **fat-soluble vitamin**. - Impaired fat absorption in cholestasis would reduce vitamin A uptake, contributing to night blindness. *Increased prothrombin time and easy bleeding* - These symptoms are indicative of **vitamin K deficiency**, a **fat-soluble vitamin**. - Vitamin K is essential for the synthesis of clotting factors, and its absorption is severely hindered in cholestasis, leading to coagulopathies.

Question 8: A child presents with rachitic changes in the limbs that are not responding to Vitamin D supplementation. Investigations reveal the following results: - Calcium: $9.5 \mathrm{mg} / \mathrm{dl}$ - Phosphorus: $1.6 \mathrm{mg} / \mathrm{dl}$ - Alkaline phosphatase (ALP): 814 IU - Serum PTH: $24.2 \mathrm{pg} / \mathrm{ml}$ - Serum electrolytes, creatinine, and blood gases: Normal. What is the most likely diagnosis?

A. Hypophosphatemic rickets (Correct Answer)
B. Vitamin D-dependent rickets type 2
C. Vitamin D-dependent rickets type 1
D. Chronic renal failure
E. Vitamin D deficiency rickets

Explanation: ***Hypophosphatemic rickets*** - The combination of **rachitic changes** not responding to Vitamin D, **low serum phosphorus (1.6 mg/dl)**, and **normal calcium and PTH levels** strongly points to hypophosphatemic rickets, a condition characterized by impaired renal phosphate reabsorption. - The **elevated alkaline phosphatase** indicates increased bone turnover as the body tries to mineralize bone despite phosphate deficiency. *Vitamin D-dependent rickets type 2* - This condition involves resistance to **1,25-dihydroxyvitamin D**, leading to **hypocalcemia** and elevated PTH, none of which are present here. - It would also typically show an inadequate response to Vitamin D, but the primary biochemical derangement is different. *Vitamin D-dependent rickets type 1* - This type is caused by a defect in **1-alpha-hydroxylase**, leading to an inability to convert 25-hydroxyvitamin D to its active form, resulting in **hypocalcemia** and elevated PTH, which are not observed. - It would also show a poor response to standard Vitamin D supplementation. *Vitamin D deficiency rickets* - This is the most common form of rickets caused by inadequate Vitamin D intake or synthesis, presenting with **hypocalcemia**, **elevated PTH**, and **low phosphorus**. - However, it typically responds well to Vitamin D supplementation, unlike the presentation here, and would show elevated PTH levels. *Chronic renal failure* - Chronic renal failure would present with **elevated creatinine**, and typically leads to **secondary hyperparathyroidism** (elevated PTH), **hyperphosphatemia**, and metabolic acidosis, none of which are suggested by the provided lab results. - The serum electrolytes, creatinine, and blood gases are explicitly stated as normal.

Question 9: A 65-year-old female with chronic renal failure presents with recent onset of bone pain. Serum analysis reveals decreased levels of calcium and elevated levels of parathyroid hormone. One of the mechanisms driving the elevated PTH is most similar to that seen in:

A. Decreased functioning of the calcium-sensing receptor (CASR)
B. Sarcoidosis
C. Parathyroid adenoma
D. End stage liver failure
E. Insufficient Ca intake (Correct Answer)

Explanation: ***Insufficient Ca intake*** - **Chronic renal failure** impairs the kidney's ability to activate **vitamin D**, leading to **decreased calcium absorption** from the gut. - This resulting **hypocalcemia** stimulates the parathyroid glands to increase **PTH secretion** to normalize calcium, a response similar to that seen with insufficient dietary calcium intake. *Decreased functioning of the calcium-sensing receptor (CASR)* - A dysfunctional CASR would lead to **hypercalcemia** and inappropriately normal or elevated PTH, as the parathyroid gland would not recognize normal or high calcium levels. - In chronic renal failure, the primary issue is **hypocalcemia** leading to secondary hyperparathyroidism, not a problem with calcium sensing itself. *Sarcoidosis* - Sarcoidosis can cause **hypercalcemia** due to extrarenal production of **1,25-dihydroxyvitamin D** (calcitriol) by activated macrophages. - This condition would typically lead to **suppressed PTH levels**, which is the opposite of the elevated PTH seen in the patient's case. *Parathyroid adenoma* - A parathyroid adenoma causes **primary hyperparathyroidism**, characterized by **hypercalcemia** and inappropriately high PTH levels. - The patient in the vignette presents with **hypocalcemia**, making primary hyperparathyroidism less likely as the direct cause of the elevated PTH. *End stage liver failure* - Liver failure can impair **vitamin D hydroxylation** in the liver, leading to **decreased 25-hydroxyvitamin D** levels. - While this can contribute to hypocalcemia and elevated PTH (secondary hyperparathyroidism), it is distinct from the primary mechanism in renal failure involving the kidney's crucial role in **1-alpha hydroxylation** of vitamin D.

Question 10: A 68-year-old man comes to the physician because of fatigue and muscle cramps for the past 4 weeks. He has also noticed several episodes of tingling in both hands. He has not had fever or nausea. He has had a chronic cough for 10 years. He has chronic bronchitis, hypertension, and osteoarthritis of both knees. His father died from lung cancer. Current medications include salbutamol, ibuprofen, and ramipril. He has smoked 1 pack of cigarettes daily for 45 years. He is 175 cm (5 ft 9 in) tall and weighs 68 kg (163 lb); BMI is 22 kg/m2. His temperature is 36.7°C (98°F), pulse is 60/min, and blood pressure is 115/76 mm Hg. While measuring the patient's blood pressure, the physician observes carpopedal spasm. Cardiopulmonary examination shows no abnormalities. His hematocrit is 41%, leukocyte count is 5,800/mm3, and platelet count is 195,000/mm3. Serum alkaline phosphatase activity is 55 U/L. An ECG shows sinus rhythm with a prolonged QT interval. Which of the following is the most likely underlying cause of this patient's symptoms?

A. Multiple endocrine neoplasia
B. Ectopic hormone production
C. Medication side effect
D. Destruction of parathyroid glands
E. Vitamin D deficiency (Correct Answer)

Explanation: ***Vitamin D deficiency*** - The patient's symptoms of **fatigue**, **muscle cramps**, **paresthesias** (tingling in hands), and **carpopedal spasm** (Trousseau's sign) are classic manifestations of **hypocalcemia**. - The **prolonged QT interval** on ECG further confirms hypocalcemia. - **Vitamin D deficiency** is the most common cause of hypocalcemia in elderly patients, especially those with: - **Chronic disease** (chronic bronchitis) - **Limited sun exposure** (likely given chronic illness) - **Poor nutrition** or malabsorption - **Normal alkaline phosphatase** (55 U/L) helps rule out severe bone disease - This is the most likely diagnosis given the clinical presentation and demographic factors. *Multiple endocrine neoplasia* - **MEN syndromes** (MEN1, MEN2a) typically cause **primary hyperparathyroidism** with **hypercalcemia**, not hypocalcemia. - There is no evidence of other endocrine tumors or family history to suggest MEN. *Ectopic hormone production* - **Ectopic PTHrP production** (e.g., from squamous cell lung carcinoma) causes **hypercalcemia**, not hypocalcemia. - While the patient has smoking history and chronic cough, his presentation is clearly hypocalcemia. *Medication side effect* - The patient's current medications (**salbutamol**, **ibuprofen**, **ramipril**) are not commonly associated with symptomatic hypocalcemia. - None of these medications typically cause carpopedal spasm or prolonged QT interval from calcium disturbances. *Destruction of parathyroid glands* - **Hypoparathyroidism** from parathyroid destruction (surgical, autoimmune, or infiltrative) would cause hypocalcemia. - However, there is **no history** of neck surgery, radiation, or autoimmune disease. - Without such history, this is less likely than vitamin D deficiency in an elderly patient with chronic disease.

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