Define and contrast osteoporosis and osteomalacia.
Both osteoporosis and osteomalacia can cause weak bones.
In osteoporosis, there is decreased bone mass with a normal ratio of mineral to matrix.
In this iliac crest biopsy, above, osteoporosis is inferred by the small amount of bone (seen in black)
In osteomalacia, the ratio of mineral to matrix is decreased (ie there is too much matrix relative to the amount of bone)
In this iliac crest biopsy, below, osteomalacia is seen. there is lots of OSTEOID (matrix, red) vs bone (again seen in black)
Osteoporosis causes decreased bone mass, with a normal ratio of bone mineral to matrix in addition to altered bone microarchitecture. The catch-phrase of osteoporosis is "normal-enough bone, but not enough of it!"
Clinical features of osteoporosis include fractures from minimal trauma, particularly in the thoracic and lumbar spine, wrist and hip.
Thoracic vertebral compression fractures can cause dorsal kyphosis (Dowager's hump).
Plain x-rays show decreased bone density; but only once at least 30% of bone is lost. Dual-energy x-ray absorptimoetry (DEXA) is the diagnostic test for osteoporosis; it reports bone density in terms of T scores, representing deviations from the mean of normal individuals). A DEXA > 2.5 is diagnostic of osteoporosis. Lab values of serum calcium, phosphorus and alakaline phosphatase are not diagnostic.
Osteomalacia is characterized by a decreased ratio of bone mineral to matrix.
Osteomalacia when it appears in children is called rickets", seen below
Histologically, the un-mineralized osteoid appears as a thickened layer of matrix. The disease causes characteristic symptoms of diffuse bone pain, tenderness and muscle weakness. X-rays commonly show decreased bone density with thinning of the cortex. Advanced disease can cause concavity of vertebral bodies (codfish vertebrae) and bowed legs.
In addition, fissures/cracks (so-call Looser's zones) may appear. These are incomplete fractures, as shown below, are filled with the un-mineralized osteoid seams.
Lab findings may show low serum and urinary calcium and high serum alkaline phosphate.