From the Guidelines
In osteomalacia, characteristic laboratory findings include low serum calcium, low phosphorus, elevated alkaline phosphatase (ALP), and elevated parathyroid hormone (PTH) levels, as seen in the patient with suspected osteomalacia who has generalized bone pain, loose bulky stools, muscle weakness, and a distended abdomen, with X-ray films showing generalized demineralization of bones, absence of the lamina dura, and fracture-like lines in the bones of the feet 1.
Biochemical Changes
The effects on calcium, phosphorus, alkaline phosphatase (ALP), and parathyroid hormone (PTH) levels in a patient with suspected osteomalacia can be summarized as follows:
- Calcium levels decrease due to inadequate vitamin D, which impairs intestinal calcium absorption.
- Phosphorus levels drop because vitamin D deficiency reduces phosphate absorption and secondary hyperparathyroidism increases renal phosphate excretion.
- ALP rises as osteoblasts increase production to compensate for impaired bone mineralization.
- PTH elevates as a compensatory mechanism to the low calcium levels, attempting to restore calcium homeostasis by increasing bone resorption, enhancing renal calcium reabsorption, and promoting phosphate excretion.
Pathophysiology
These biochemical changes reflect the underlying pathophysiology of osteomalacia, where inadequate bone mineralization occurs despite normal bone matrix formation, typically due to vitamin D deficiency, phosphate deficiency, or mineralization defects 1.
Treatment Implications
The treatment of osteomalacia involves addressing the underlying cause of the disease, such as vitamin D deficiency or phosphate deficiency, and may include supplementation with vitamin D and phosphate, as well as other measures to promote bone health 1.
Key Findings
Key findings in osteomalacia include:
- Low serum calcium and phosphorus levels
- Elevated ALP and PTH levels
- Generalized demineralization of bones on X-ray
- Absence of the lamina dura on X-ray
- Fracture-like lines in the bones of the feet on X-ray These findings are consistent with the diagnosis of osteomalacia and highlight the importance of prompt treatment to prevent further bone damage and improve quality of life 1.
From the Research
Effects on Calcium, Phosphorus, Alkaline Phosphatase, and Parathyroid Hormone
- Calcium levels are typically low in patients with osteomalacia, as seen in the case of a 17-year-old Filipino male hemodialysis patient 2.
- Phosphorus levels are also reduced in osteomalacia, often due to a disturbed phosphate metabolism, as mentioned in a study on metabolic bone disease osteomalacia 3.
- Alkaline phosphatase (ALP) levels are typically elevated in osteomalacia, as noted in a study on osteomalacia 3 and another on the complexities of osteomalacia 4.
- Parathyroid hormone (PTH) levels can be increased in osteomalacia, particularly in cases of secondary hyperparathyroidism, as observed in a patient with adult-onset vitamin D-resistant osteomalacia 5.
Biochemical Assessment
- A full biochemical assessment of mineral metabolism is necessary to diagnose osteomalacia, including measurements of serum calcium, phosphorus, ALP, and PTH levels, as well as 25-hydroxycholecalciferol (25OH-vitamin D) levels 2, 4.
- Both too-high and too-low serum ALP levels can be important for diagnosis, highlighting the complexity of osteomalacia 4.
Treatment and Management
- Treatment strategies for osteomalacia comprise supplementation of vitamin D and calcium, and for patients with intestinal malabsorption syndromes, vitamin D and calcium are also given parenterally 3.
- In cases of renal phosphate wasting syndromes, substitution of phosphate is the treatment of choice, except for tumor-induced osteomalacia, where removal of the tumor can lead to a cure in most cases 3.