crowds out the BONE MARROW. BONE MARROW TRANS-
PLANTATIONis at present the only successful treat-
ment for infantile osteopetrosis but itself carries
significant risk.
Adult-onset osteopetrosis is present from birth
but does not cause symptoms until adulthood
when the abnormalities of bone structure are
advanced enough to become apparent. Many
adults who have osteopetrosis do not have overt
symptoms and discover they have the disorder
when receiving treatment for another condition
for which the doctor requests an X-RAY. X-ray pro-
vides definitive diagnosis as osteopetrosis has a
distinct, characteristic presentation. There are no
treatments for adult-onset osteopetrosis other
than efforts to reduce the risk for fracture. Adult-
onset osteopetrosis increases the risk for
OSTEOMYELITIS(INFECTIONof the bone), which is one
of the common reasons people initially seek med-
ical care.
See also GENETIC DISORDERS; INHERITANCE PATTERN;
MUTATION; OSTEOMALACIA; OSTEOPOROSIS.
osteoporosis A condition of diminished BONE
DENSITY(the extent of mineralization of the bones).
Though some loss of mineralization is a normal
process of aging, osteoporosis represents an accel-
erated loss that causes health problems. Osteo-
porosis weakens the BONEstructure; increases the
risk for FRACTURE; and may result in bone deformi-
ties, particularly of the spine. The spine and hip
are most vulnerable to fracture. Osteoporosis typi-
cally affects women after MENOPAUSE, though may
develop earlier in women who do not produce
estrogen, and men age 75 and older. About 10
million Americans have osteoporosis, 80 percent
of whom are women.
Osteoporosis appears to primarily affect women
for two reasons: estrogen and body size.
Researchers do not fully understand how estrogen
protects bone health but they do know that when
estrogen levels fall dramatically, as with
menopause, bone demineralization accelerates. As
well, women have inherently less body mass—
bone mass and MUSCLEmass—than men. Some
researchers theorize that bone demineralization
takes longer to affect men because their larger
skeletons can withstand a greater loss of calcium
before becoming thin and weak.
Symptoms and Diagnostic Path
Early indications of accelerated bone loss include
loss of more than^1 ⁄ 2 inch in height and develop-
ment of kyphosis (hump in the middle of the
back). However, these signs develop slowly and
over considerable time, often several decades,
which makes them less apparent. Health experts
call osteoporosis a silent disease because there are
few indications of its presence until it is well
established. Often the first symptom of osteoporo-
sis is an unexpected fracture. The wrist, spine, and
hip are the most vulnerable sites for fracture. X-
RAYshows a characteristic porous structure to the
bones, demonstrating the loss of mineral content
and bone mass. Bone density tests such as DEXA
scan can detect demineralization before fracture
occurs.
Doctors use a scale of relative percentage of
bone loss to measure the severity of osteoporosis.
The scale represents bone loss as a standard devia-
tion (SD) from the accepted norm for optimal
healthy bone mass. An SD value of –2.5 or greater
(2.5 SDs below the norm) is diagnostic for osteo-
porosis. Testing facilities report this value as a T-
score; the norm for comparison is the bone
density of a young healthy person of the same
gender. Another representation is the Z-score,
which compares the person’s bone density to that
of the norm for others of the same age and gen-
der. Some testing facilities report bone loss as a
percentage; a –2.5 SD value represents about a 35
percent loss of bone density (bone mass is 65 per-
cent of what it should be).Treatment Options and Outlook
Weight-bearing and RESISTANCE EXERCISEis essential
to stimulate bone remodeling activity. For estab-
lished osteoporosis treatment focuses on decreas-
ing the resorption of bone to increase bone mass.
Several kinds of medications can achieve this
effect. Among them are calcium and vitamin D
supplements, estrogen supplements, bisphospho-
nates, PARATHYROID HORMONE supplement, CALCI-
TONINsupplement, and Selective estrogen receptor
modulators (SERMs). Individual circumstances
determine which treatment approaches are most
appropriate.
Calcium and vitamin D The body’s ability to
absorb dietary calcium diminishes with advancingosteoporosis 345