Discussion Topic #2: Calcium Homeostasis (Endocrine System)

Case Study: Calcium Homeostasis 

Introduction: Patient Case Summary

During a 62-year old female patient’s yearly physical exam, your colleague at the clinic asks for your input regarding the patient’s case. The patient has asked for a second opinion so your colleague provides you with the following information:

• Issues with recurring kidney stones AND calcium in her urine;
• Bone density scan shows significant bone thinning;
• Blood work shows significant elevation of serum calcium at 16.5 mg/dl (normal reference range for postmenopausal females: 8.4-10.7 mg/dl);
• Vitamin D-25 deficiency;
• Patient complains of other non-specific symptoms: increased fatigue, sleep issues, difficulty in concentrating, and loss of initiative.

Collaboration: Patient seeks second-opinion

Your colleague dismisses the non-specific symptoms as related to possible depression and/or anxiety. He also thinks that the LOW vitamin D-25 is the cause  of the LOW serum calcium levels.

Also, he believes that the decreased bone density means she has osteoporosis. His plan is to prescribe an anti-depressant ,with possible referral to a psychiatrist, medication for osteoporosis, and a vitamin D supplement. 

Your keen critical thinking abilities and expertise in human physiology means that you don’t agree with this analysis. You respectfully disagree and tell your colleague that he is missing the full picture.  In particular, you refer your colleague to review calcium homeostasis mechanisms which do not support his conclusion that low vitamin D-25 causes low serum calcium. 

Patient Follow-up #1: Next Steps

Rather than dismissing the patient’s neuropsychiatric symptoms as simply depression, your position is that these must be considered in the context of the recurring kidney stones, elevated serum calcium, and bone thinning.

You explain to the patient that it is important to connect the dots to see the full picture. Based on the preliminary labs done and her bone density scan, you note that there must be something wrong with calcium homeostasis.

In fact, you also share with the patient that the latest medical publications, discuss that patients with these test results combined with the neuropsychiatric symptoms are most likely experiencing primary hyperparathyroidism (PHPT).

After explaining this to the patient, she asks you to consult on her case and what should be done next.

You order follow-up blood work to check parathyroid hormone levels, along with serum calcium and vitamin D. You also order a radiologic work-up of her parathyroid glands. 

Patient Follow-up #2: Diagnostic Test Results & Diagnosis

The labs reveal significant elevation of PTH and confirm elevated serum calcium levels with vitamin D deficiency.  The scan shows a growth on her parathyroid glands, most likely a benign parathyroid adenoma.

All this data confirms the diagnosis of: Primary Hyperparathyroidism (PHPT).

Now, you are meeting the patient to discuss these results and her diagnosis.

The patient is confused and asks you to explain what you mean by “calcium homeostasis.” She also doesn’t understand why her PTH is high, Ca2+ is high, but vitamin D is low.

She needs your support by explaining the mechanisms involved in the physiological regulation of calcium homeostasis. You schedule a follow-up meeting in your office to explain these mechanisms.

Questions

Calcium homeostasis is critical for maintaining healthy body functions. 

In preparation for your patient meeting, please examine the mechanisms for endocrine regulation of calcium homeostasis and apply your understanding by answering the following:

**Note: These questions may be answered using our class resources – Ch. 11 lecture discussion, PPT notes, and textbook.

1. Identify the two major hormones in humans that are critical for regulating calcium homeostasis.
2. Explain the step-by-step mechanisms by which these hormones increase extracellular calcium concentration.
3. Based on your understanding of  #1 & #2, briefly explainhow the patient’s high levels of PTH are leading to decreased bone density.

Discussion Topic #2: Calcium Homeostasis (Endocrine System) Answer

1. The two main hormones that regulate calcium homeostasis are Parathyroid hormone and 1,25-dihydroxyvitamin D (1,25-(OH)₂D). The parathyroid hormone is a protein hormone that is produced by the parathyroid gland, and consequently increases the extracellular Ca2+ concentration. On the other hand, (1,25-(OH)₂D) is the hormonal form of Vitamin D, and comes directly from the kidneys. It works mainly to increase the intestinal absorption of Ca2+.