Key Clinical Updates in Rickets & Osteomalacia
Patients with high FGF-23 levels can have genetic testing for X-linked hypophosphatemic rickets (PHEX), autosomal dominant hypophosphatemic rickets (FGF23), and autosomal recessive hypophosphatemic rickets (DMP1).
In hypophosphatemic patients without such mutations, searching for a tumor causing tumor-induced osteomalacia is reasonable, particularly in patients with bone pain or fractures.
Such tumors are typically small and may be located anywhere, so they are best localized using a whole-body DOTATATE-PET/CT scan.
For patients with tumoral hypophosphatemia, resection of the tumor normalizes serum phosphate levels, but about 20% experience recurrence, usually in the same location.
With both tumoral and genetic FGF-23-related hypophosphatemia, therapy with burosumab improves osteomalacia.
For patients who cannot take burosumab or who continue to have hypophosphatemia, oral phosphate supplements must be given long-term; oral phosphate causes diarrhea at higher doses, however, so many patients do not achieve normal serum phosphate levels. Calcitriol, 0.25–0.5 mcg daily is given to improve the impaired calcium absorption caused by the oral phosphate.
Patients with hypophosphatasia may be treated with asfotase alfa (Strensiq). Teriparatide can improve bone pain and fracture healing. Bisphosphonates are contraindicated.
ESSENTIALS OF DIAGNOSIS
Low bone density from defective mineralization.
Caused by deficiency in calcium, phosphorus, or low alkaline phosphatase.
Rickets: defective bone mineralization in childhood or adolescence before epiphyseal fusion.
Osteomalacia: defective bone mineralization in adults with fused epiphyses.
Painful proximal muscle weakness (especially pelvic girdle); bone pain.
Low serum 25-hydroxy-vitamin D (25-OHD), hypocalcemia, hypocalciuria, hypophosphatemia, secondary hyperparathyroidism.
Classic radiologic features may be present.
Defective mineralization of the growing skeleton in childhood causes permanent bone deformities (rickets). Defective skeletal mineralization in adults is known as osteomalacia. It is caused by inadequate calcium or phosphate mineralization of bone osteoid.
Causes of osteomalacia are listed in Table 26–11.
Table 26–11.Causes of osteomalacia.1 ||Download (.pdf) Table 26–11. Causes of osteomalacia.1
Insufficient sunlight exposure
Kidney: chronic kidney disease, nephrotic syndrome, kidney transplantation
Nutritional deficiency of vitamin D
Malabsorption: aging, excess wheat bran, bariatric surgery, pancreatic enzyme deficiency, orlistat
Vitamin D–dependent rickets types I and II
Phenytoin, carbamazepine, valproate, or barbiturate therapy (long-term)
Dietary calcium deficiency
Fanconi syndrome, renal tubular acidosis, and alcoholism
Nutritional deficiency of phosphorus
Phosphate-binding antacid therapy
Tumoral hypophosphatemic osteomalacia
X-linked hypophosphatemic rickets
Other disorders, including paraproteinemias, glycogen storage diseases, neurofibromatosis, Wilson disease
Inhibitors of mineralization
Disorders of bone matrix
Vitamin D is predominantly synthesized in the skin during exposure to ultraviolet B light (Table 26–11). Vitamin D is also consumed in the diet from plants (ergocalciferol, D2) or ...