**Question:** A 65-year-old woman with type 2 diabetes is on hemodialysis for chronic kidney disease. She now presents to the clinic with symptoms of pain in the hands. The symptoms started many months ago and are now getting worse. She does not recall any injury to the hands and has not noticed any swelling or redness in the joints. On examination, the joints are normal with no inflammation or tenderness on palpation. There is full range of motion of the fingers and wrists. Laboratory investigations: calcium (7.2 mg/dL), phosphate (5.5 mg/dL), and PTH level (710 ng/L). (See Figure below) What is the most likely diagnosis?

A. Hypocalcemia
B. Hyperphosphatemia
C. Hyperparathyroidism
D. Hypoparathyroidism

**Correct Answer:** D. Hypoparathyroidism

**Core Concept:**
The presented case describes a patient with chronic kidney disease and type 2 diabetes on hemodialysis. This patient presents with symptoms of pain in her hands, which are consistent with a parathyroid hormone (PTH) deficiency. PTH is produced by the parathyroid glands and plays a crucial role in maintaining calcium and phosphate homeostasis in the body.

**Why the Correct Answer is Right:**
The correct answer is Hypoparathyroidism (Option D) because the patient exhibits symptoms of low calcium levels (hypocalcemia) despite normal calcium levels (7.2 mg/dL) and high phosphate levels (5.5 mg/dL). The elevated PTH level (710 ng/L) indicates the body is trying to compensate for the low calcium levels by increasing PTH production. However, the primary cause of these symptoms is the deficiency of PTH, which is why the patient has low calcium levels in spite of normal PTH levels.

**Why Other Options are Incorrect:**

A) Hypocalcemia (Option A) is incorrect because the patient's calcium levels (7.2 mg/dL) are within the normal range.

B) Hyperphosphatemia (Option B) is incorrect because the patient's phosphate levels (5.5 mg/dL) are elevated, indicating that the body is trying to counteract the hypocalcemia by increasing PTH production.

C) Hyperparathyroidism (Option C) is incorrect because elevated PTH levels (710 ng/L) suggest that the patient has a deficiency of PTH, not an excess of PTH.

**Clinical Pearls:**
Hypoparathyroidism is a rare condition that can occur in patients with chronic kidney disease on hemodialysis, as seen in this case. This condition presents with symptoms of hypocalcemia, despite normal calcium levels and elevated PTH. The elevated PTH levels are a compensatory response to the hypocalcemia. This case highlights the importance of considering differential diagnoses when evaluating patients with atypical presentations, especially in the context of certain comorbidities like chronic kidney disease.