Primary Biliary Cirrhosis (cont.)
In this Article
Metabolic Bone Disease
Patients with PBC may experience pain in the bones of their legs, pelvis,
back (spine), or hips. This bone pain can come from one of two bone diseases,
osteoporosis (sometimes referred to as thin bones) or osteomalacia (soft bones).
Patients with PBC have a 440% increase in the likelihood of having poorly
calcified bones compared to normal people of the same age and gender. Most
people with osteoporosis or osteomalacia, however, do not have bone pain. Still,
a minority do experience bone pain that can be severe, often due to bone
fractures.
Poorly calcified bones (osteopenia) characterize both osteoporosis and
osteomalacia. The cause of the osteopenia in osteoporosis, however, is not
known, although the development of osteoporosis tends to speed up in women after
the onset of menopause. In osteoporosis, there is chronic, accelerated loss of
calcium and protein from the bones. By contrast, in osteomalacia, the osteopenia
results from failure of the bones to calcify. The cause of osteomalacia is
vitamin D deficiency.
While the body's processing (metabolism) of dietary calcium and vitamin D
is normal in PBC, bone metabolism is abnormal. Normal bone metabolism involves
an ongoing balance among production of new bone, calcification of bone, and loss
of bone. Vitamin D plays a key role in regulating the deposition of calcium in
bone. What then, causes the deficiency of vitamin D in PBC? First of all,
patients with PBC and advanced cholestasis, usually recognized by significant
jaundice, can have a decreased ability to absorb dietary vitamin D from the gut.
(Please see the section on fat malabsorption and jaundice.) Additionally, poor
pancreatic function, celiac sprue, and scleroderma with bacterial overgrowth may
be present in some patients with PBC. Each of these conditions can further
impair the ability to absorb dietary vitamin D from the intestines.
The resulting vitamin D deficiency is the cause of the decreased deposit of
calcium in the bones in osteomalacia. All of this said, compared to
osteoporosis, osteomalacia is rare, especially among patients who are exposed to
sunlight throughout the year. That's because sunlight stimulates the
production of vitamin D in the skin, which can compensate for the poor
absorption of vitamin D from the diet.
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