Changes in Bone Density: Decreased

10.1055/b-0034-87945

Changes in Bone Density: Decreased

Several terms are commonly used to describe the decreased density of bones. Osteoporosis is a disease of reduced bone mineral density that leads to fracture and is defined as measured by dual energy X-ray absorptiometry or quantitative CT. Osteomalacia describes bone softening due to defective bone mineralization. In children, osteomalacia is known as rickets, and because of this the term osteomalacia is often restricted to the adult form of the disease. Although many of the features of osteoporosis and osteomalacia overlap, they are distinct disorders.

Osteomalacia is a defect in mineralization of osteoid, the protein framework in bones, and is usually the result of low vitamin D levels. Osteopenia is a term for low bone mineral density and may be a precursor to osteoporosis.

**Table 5.92 Bone density: decreased**
Diagnosis	Findings	Comments
Osteopenia from disuse	Regional decreased bone density involving immobilized limbs. Cortex is diffusely thinned and the trabeculae are rarified. Metaphyseal ends may be sharply defined.	Commonly observed during immobilization after trauma/fracture. May accompany soft-tissue atrophy in chronic disuse, arthrogryposis, and other degenerative disorders of muscle and nerves.
Rickets Fig. 5.177, p. 618 Fig. 5.178, p. 618 Fig. 5.4, p. 496 Fig. 5.62, p. 537 Fig. 5.69, p. 542	Skeletal changes depend on the patient’s age. Wide and hazy growth plates, ill-defined architecture of the trabeculae. Hazy metaphyseal end plates with cupping.	All forms of rickets (vitamin D–deficiency, renal osteodystrophy, vitamin D–resistance, etc). Cortical erosions occur in secondary hyperparathyroidism.
Steroid therapy Fig. 5.113, p. 573	Systemic decrease in bone density. Cortex is diffusely thinned and the trabeculae are rarified.	Decrease in osteoblast activity relative to osteoclasts.
Hematologic disorders	Systemic decrease in bone density may be accompanied by changes characteristic for a particular disorder (e.g., hair-on-end skull in thalassemia major).	Proliferation of cells or deposition of metabolites replaces bone. DD: sickle cell disease, thalassemia major, lysosomal storage disease, leukemia, mastocytosis, mucolipidosis.
Diffuse metastatic disease Fig. 5.179, p. 618	Diffuse bone demineralization may mask lytic lesions.	Pathologic fractures.
JIA	Periarticular bone demineralization.	Demineralization may be accompanied by soft-tissue swelling (synovial hypertrophy), joint space narrowing, and/or periarticular erosions.
Scurvy	(see Table 5.43 )
Hyperphosphatasia	Meshed radiolucent bone texture.	Progressive skeletal deformity. Enlargement and thickening of the skull and bowed limbs. High levels of serum alkaline phosphatase.
Congenital hyperparathyroidism	Pronounced bone demineralization, cortical erosions, and Trümmerfeld fractures in the metaphyses.	Coarse bone trabeculae, subperiosteal bone resorption, and metaphyseal cupping.
Osteogenesis imperfecta types I and IV	Diffuse osteopenia
Idiopathic juvenile osteoporosis	Disseminated osteoporosis and vertebral body collapse. Presents with bone pain between 8–14 y of age. May spontaneously resolve.
Homocystinuria	(see Table 5.45 )
Metaphyseal chondrodysplasia, Jansen type	Osteopenia in 70%. Extensive irregularity in mineralization of markedly expanded and cup-shaped metaphyses.	Relatively preserved epiphyses. The deformity of the metaphyses decreases in adult life.