Bones, Calcium, Phosphate, and PTH in Kidney Failure - Bone disease due to high PTH (Renal Osteodystrophy)
|Bone disease due to high PTH (called Renal Osteodystrophy) |
Adynamic bone disease
Bone disease due to high PTH (Renal Osteodystrophy)
This is the type of bone disease that occurs when the blood levels of PTH have been very high for a long time. PTH removes calcium from the bones, and the bones try to repair themselves, but cannot do so very effectively. In the early stages, all that can be seen are changes under the microscope if a bit of bone is removed for examination (a bone biopsy).
All kidney doctors try to prevent advanced renal osteodystrophy by medical treatment and parathyroidectomy. Preventative treatment does work, so that the frightening list of problems listed below is seldom seen.
Advanced renal osteodystrophy causes weakness and loss of bones, which can be irreversible. There is a tendency to fracture of bones. Also, bone tissue it lost, especially from the tips of the fingers and ends of the collar bones. This can cause stubby fingers and hunched shoulders. The spine can also be affected, causing curvature. As other bones try to repair themselves, there can be pain around the hips and shoulders, and broadening of the cheekbones and coarsening of the skin.
Adynamic bone disease
Adynamic bone disease is not fully understood. Although the bones may have normal strength and overall appearance, they are under active. Normally bone is quite active, with constant reabsorption of bone and laying down of bone. In adynamic bone disease, both the reabsorption and laying down processes are slow. This may not be harmful to the bones themselves. Certainly in the short term, severe problems do not seem to develop.
However, the bones cannot help keep blood levels of calcium normal by soaking up calcium from the blood when levels are high. Therefore people with adynamic bone disease are prone to high calcium levels, and may be at increased risk of calciphylaxis. It is therefore necessary to monitor the levels of calcium and phosphate very carefully in this condition. PTH levels are normal.
Osteoporosis means thin bones. Most people have heard of this condition, because it is very common in the general population. It is also a problem in people with kidney diseases.
Osteoporosis, by itself, usually causes no problems. It is not until a bone breaks or a backbone is compressed that problems are recognised. Therefore there is an increasing tendency to check people with kidney disease for thin bones before any problems develop.
Thin bones can result in fractures, especially of the hip or wrist. Also, if the back is very osteoporotic, the backbones can get squashed or have compression fractures. This can lead to a loss of height, bent back and back pains (NB. there are many other causes of back pain).
Osteoporosis is found especially in women who have gone through the menopause, people who are immobile, and those who have been on steroids tablets (prednisolone) for a long time.
Osteoporosis is diagnosed by a special X-ray called a DEXA scan, and if you are at risk, kidney units may screen patients at high risk of osteoporosis with these scans.
The treatment for osteoporosis consists of sensible exercise (the bones get stronger if they are used), a good diet and stopping smoking. If someone is taking steroid tablets, it may be possible to stop them. Women may benefit from hormone replacement therapy and, finally, there are drugs which can strengthen bones.
Osteoarthritis is one of the commonest forms of arthritis, and occurs in people with kidney trouble just as it does in the general population.
Joints are affected, most commonly the knees, hips and hands. There is not enough space here to discuss osteoarthritis at length, (Click here to link to the Arthritis Research Campaign (UK) where there is more information, including downloadable leaflets).
A particular problem with osteoarthritis in people with kidney trouble is the treatment for pain. Painkilling drugs most suitable for people with osteoarthritis can damage kidneys, and must either be avoided or used with extreme caution. These drugs are the NSAIDS (non-steroidal anti-inflammatory drugs). They are often prescribed, but can be purchased without prescription as ibuprofen (often under the trade names Nurofen or Advil). More details and alternatives to these drugs are given elsewhere on this website (click here)
Amyloid is a general term for a range of conditions where there is microscopic deposition of material in the tissues of the body. It has a particular appearance under the microscope. There are several causes of amyloid, and it is described elsewhere on this website (click here)
One particular type of amyloid can cause problems in people who have been on dialysis for over 10 years. It is called dialysis amyloid. Dialysis amyloid is caused by the build up of a chemical called beta-2 microglobulin. This normally passes out of the body through the kidneys. However, the plastic membranes used in haemodialysis are not as efficient as the human kidney, so that beta-2 microglobulin is not removed well by haemodialysis. Peritoneal dialysis removes it reasonably well, but dialysis amyloid can also occur if someone has been on peritoneal dialysis for many years.
The first sign of dialysis amyloid is usually around the wrist. Amyloid can build up and press on the nerve that supplies the thumb and first two fingers, causing weakness and pins and needles. This is called carpal tunnel syndrome (there are other causes of this apart from amyloid). An operation can reduce the pressure.
Dialysis amyloid can also cause weakness in the bones around the hips, or in the neck.
Dialysis amyloid is hard to treat. If there is a successful kidney transplant, the excess beta-2 microglobulin passes out of the body quickly. This is the only really effective treatment. By using a high-flux dialysis membrane and long hours of haemodialysis, it may be possible to reduce the effects of dialysis amyloid in some cases.
Infections in the bones or joints are rare, but can be seen in people with kidney trouble. If someone on haemodialysis is prone to getting infections in the blood (perhaps because a plastic tube in the vein is used for dialysis), there is a risk. Infections may cause a joint to become enlarged and red, or cause the development of a severe and unusual pain in the hip or back. Treatment with antibiotics is effective, though surgery or removal of fluid from joints using needles may be needed.
Gout occurs in joints, which become suddenly swollen, red hot and very, very painful. Gout is caused by the build-up of a chemical called uric acid in the blood. This is normally removed by the kidneys, so gout can occur as kidney failure develops. Also, gout is common in people with kidney transplants, because some of the anti-rejection drugs cause retention of uric acid in the blood.
Sometimes uric acid can deposit in tissues outside joints, usually in the fingers or toes. A swelling containing a white cheesy material develops.
The treatment of gout is with painkillers, followed by preventative treatment once the painful attack has settled down. In kidney disease, anti inflammatory medications are avoided so a medication call colchicine is used. Sometimes steroid therapy is used to as an anti-inflammatory treatment as well.
Preventative treatment is usually effective with a drug called allopurinol. Unfortunately this cannot be used in people with kidney transplants who are treated with azathioprine, because of a serious drug interaction, but it is possible to change this medication to alternative medication if allopurinol is necessary.
The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.