Review Question - QID 220685

This patient who presents with a low-energy femoral neck lucency in the setting of hyperphosphatemia, hypocalcemia, and chronic kidney failure most likely has renal osteodystrophy.

Renal osteodystrophy represents a spectrum of diseases seen in patients with chronic renal disease. It is characterized by bone mineralization deficiency due to electrolyte and endocrine abnormalities. High turnover renal osteodystrophy is classically associated with significantly increased phosphate release from the bones to the serum. Chronic renal disease leads to a decrease in renal phosphorus excretion, which leads to phosphate retention and a significant increase in serum phosphate levels. These increased phosphate levels complex with calcium and result in decreased calcium levels. This in turn causes tertiary hyperparathyroidism.

Tejwani et al. review the evidence regarding the diagnosis and treatment of renal osteodystrophy. They discuss how high-turnover renal osteodystrophy results in increased parathyroid hormone production. They recommend medical intervention in order to normalize the underlying calcium and phosphate levels.

Figure/Illustration A is a radiograph demonstrating lucency in the inferior aspect of the femoral neck (red circle). These findings are known as Looser lines and are consistent with renal osteodystrophy.

Incorrect Answers:
Answer 1: Osteopetrosis would present with hyperdense bones. While this can result in femoral neck fractures, the calcium and phosphate levels would be normal. Treatment includes fixation of fractures and bone marrow transplant.

Answer 2: Osteoporosis would present with decreased bone mineral density that can lead to fragility fractures. This disease is primarily found in elderly women with nutritional deficiencies. Calcium and phosphate levels are typically normal in these patients. Treatment may include bisphosphonates.

Answer 3: Primary hyperthyroidism can also result in bony lesions due to abnormal mineralization of the skeleton. Patients will characteristically have brown tumors. The calcium level will be high and the phosphate level will be low. Treatment is with removing the source of parathyroid hormone production.

Answer 5: Vitamin D deficiency can also result in fragility fractures due to abnormal mineralization of bone. These patients would present with low levels of both calcium and phosphate because of decreased absorption through the gastrointestinal system. Treatment includes vitamin D repletion.

Bullet Summary:
Renal osteodystrophy would present with low calcium, high phosphate, and low energy fractures.