A 55-year-old woman presents with diffuse bone pain and muscle weakness. Laboratory tests reveal low serum calcium, low serum phosphate, and markedly elevated serum alkaline phosphatase. These findings are most characteristic of which metabolic bone disorder?

1. A

   Osteoporosis

2. B

   Osteomalacia

3. C

   Paget's disease

4. D

   Osteitis fibrosa cystica

Appeared in: NORCET 6 mains-2024

Explanation

Listen in Hindi

• The patient's laboratory results show low serum calcium, low serum phosphate, and markedly elevated alkaline phosphatase (ALP).
• This specific combination is the hallmark biochemical profile for osteomalacia.
• Osteomalacia is caused by impaired bone mineralization, most commonly due to severe vitamin D deficiency, which explains the low calcium and phosphate absorption.
• The body compensates for low calcium by increasing parathyroid hormone (PTH), which stimulates osteoblasts, leading to a rise in ALP, and also causes renal phosphate wasting.

Why Other Options Were Wrong

• Option A: In osteoporosis, the primary problem is loss of bone mass, not a defect in mineralization. Therefore, serum calcium, phosphate, and alkaline phosphatase levels are typically normal.
• Option C: Paget's disease is characterized by disorganized bone remodeling. It typically presents with a markedly elevated alkaline phosphatase, but serum calcium and phosphate levels are usually normal.
• Option D: Osteitis fibrosa cystica is a manifestation of severe hyperparathyroidism. In primary hyperparathyroidism, serum calcium is high (hypercalcemia) and phosphate is low. The patient in the scenario has low calcium.

Related Visual

Clinical Relevance

• Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Differential diagnosis of metabolic bone disorders based on laboratory findings as background academic context rather than a clinical decision trigger.
• Nurses must be able to recognize the signs of osteomalacia, including bone pain and muscle weakness, and understand the significance of the associated lab values.
• Patient education is crucial, focusing on vitamin D and calcium intake, the importance of sunlight exposure for vitamin D synthesis, and fall prevention strategies due to increased fracture risk.
• Monitoring for treatment response includes assessing for improvement in symptoms and normalization of lab values (calcium, phosphate, and ALP).

How to Approach the Question

• First, identify the key information in the clinical scenario: the patient's symptoms (bone pain, muscle weakness) and the triad of lab results (low Ca, low PO4, high ALP).
• Recognize that the question asks for the 'most characteristic' disorder, implying you need to match the full clinical and lab picture to one of the options.
• Systematically evaluate each option against the provided lab data.
• Recall or deduce the typical biochemical profiles for each metabolic bone disorder.
• For Osteoporosis, remember labs are usually normal.
• For Paget's disease, remember the isolated high ALP.

Concept Tested & Keywords

• Concept Tested: Differential diagnosis of metabolic bone disorders based on laboratory findings.
• Stem keywords: diffuse bone pain, muscle weakness, low serum calcium, low serum phosphate, elevated serum alkaline phosphatase
• Lead-in keywords: most characteristic
• Clinical cues: The combination of bone pain, muscle weakness, and the specific lab triad (low calcium, low phosphate, high ALP) is a classic presentation.
• Negative lead-in flag: false

Question ID

QpDEvLVBAWi0Z2MHxYh3Cz

Copy ID

Reference Book

E6 Medicine Davidson Principles Practice 24e p. 1073-1075

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 167-169