Differentials
Osteoporosis
SIGNS / SYMPTOMS
Both osteoporosis and osteomalacia may present with bone fractures. Typically, osteoporosis is painless and insidious until a fracture develops. Characteristically, osteomalacia is a painful bone disorder at onset.
Osteomalacia patients report a history of limited sunlight exposure, sunscreen use, malabsorption, anticonvulsant use, or renal failure. Osteoporosis typically occurs with advancing age and use of high-dose glucocorticoids.
INVESTIGATIONS
Osteoporosis typically presents with normal serum calcium, phosphorus, alkaline phosphatase, vitamin D, and PTH levels. In contrast, osteomalacia is characterized by hypophosphatemia, hypocalcemia, increased alkaline phosphatase levels, low levels of vitamin D metabolites, and secondary hyperparathyroidism.
Urinary calcium levels may be normal in osteoporosis but are low in osteomalacia. Both conditions appear as low bone mass on radiologic studies and dual-energy x-ray absorptiometry scan. However, specific radiologic findings unique to osteomalacia include Looser pseudofractures.
A bone biopsy is the best differentiating test.[55]
On x-ray, the coarseness of the trabeculae in osteomalacia may help to differentiate the 2 diagnoses.
Paget disease
SIGNS / SYMPTOMS
Most patients with Paget disease are asymptomatic. In contrast, patients with osteomalacia have bony tenderness and pain.
INVESTIGATIONS
Normal serum calcium and a markedly elevated serum alkaline phosphatase are seen in Paget disease. On x-ray, gross deformities of bone may be seen, characteristic of Paget disease, such as enlargement of the skull and bowing of the femur or tibia.
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