Why do my muscles feel weak when I am on dialysis?

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From AAKP:

Why do my muscles feel weak when I am on dialysis?

Answer: Muscle weakness is a very common complaint of dialysis patients. When muscle strength is tested, it is often reduced – even in dialysis patients who do not feel that their muscles are weak. This finding is called “uremic myopathy.” Below are several possible reasons for this muscle weakness.

Dialysis patients are less active than people with normal kidney function. Reduced activity may lead to muscle atrophy (loss of muscle – “use it or lose it”). Increased physical activity has been shown to improve performance and quality of life.

Chronic kidney disease (CKD) may lead to poor nutrition and many dialysis patients are malnourished. Studies show that muscle strength and the normal ability of muscles to relax after contracting are related to nutrition. A dialysis patient’s muscle strength can be predicted by his or her nutritional state. Dialysis patients can work with a dietician to ensure that their diet possesses enough protein and calories to maintain optimal health.

Kidney disease causes many chemical changes in the body. Chemicals that arise when kidney function fails may damage some of the body’s lipids and proteins. This “oxidative damage” may play a role in uremic myopathy. To minimize this risk, patients should receive an adequate amount of dialysis. Ask your doctor what your dialysis dose is – your Kt/V – to be sure that dialysis is adequately removing these toxins.

Dialysis patients often have abnormalities of their bones and mineral metabolism, leading to overactivity of the small parathyroid glands in the neck (hyperparathyroidism) and vitamin D deficiency and loss of calcium in the bones (osteomalacia). These conditions commonly cause muscle weakness. Treatment of these disorders with phosphate binders, active forms of vitamin D and in some cases surgical removal of parathyroid glands, can diminish muscle weakness.

Sometimes, the medicines used to treat one problem can lead to another. In the past, aluminum-containing phosphate binders, used to treat bone and mineral abnormalities, caused an aluminum build-up in the body. Bone pain and muscle weakness were common symptoms of this aluminum toxicity. Now there are more effective phosphate binders, and aluminum-containing pills are rarely used.

Anemia, or low blood count, is common in CKD and may cause fatigue and muscle weakness. Anemia can be treated with iron and erythropoetin (EPO). Most dialysis patients report that their physical function and quality of life improve when anemia is treated and normal blood count is restored.

Many dialysis patients have high blood pressure, heart disease or congestive heart failure. Muscle weakness is a common symptom of heart disease. Many medicines are available to improve heart function. In addition, patients can keep their hearts functioning more effectively by limiting fluid intake between dialysis treatments. 

Long-term hemodialysis can lead to low levels of the chemical L-carnitine and may be related to muscle weakness and other problems, such as anemia and low blood pressure, during dialysis. L-carnitine pills have been used to treat this with variable results: some studies show that they help while others do not.

Muscle weakness has been described in both hemodialysis and peritoneal dialysis. The rapid shifts of fluids and blood chemicals during hemodialysis make the dialysis treatment itself cause muscle weakness in some patients. Blood pressure sometimes falls during hemodialysis causing muscle weakness. This is particularly true if a high rate of fluid removal is required by large weight gains between treatments. In some rare cases, a sudden rise in potassium during dialysis causes profound muscle weakness.

Since CKD, or at times the dialysis procedure itself, can cause muscle weakness, a kidney transplant can be an effective cure. While not everyone with CKD is a candidate for a kidney transplant, patients should discuss transplantation with their nephrologist and healthcare team.

Answer provided by Alan S. Kliger, MD. Dr. Kliger is Clinical Professor of Medicine, Yale University School of Medicine, and Chairman, Department of Medicine Hospital of St. Raphael, New Haven, Conn.

The Dear Doctor column provides readers with an opportunity to submit renal related health questions to healthcare professionals who specialize in the area of concern. The answers are not to be construed as a diagnosis and therefore, altercations in current healthcare should not occur until the patient's physician is consulted.

This article originally appeared in aakpRENALIFE, September 2004, Vol. 20 No. 2.
http://www.aakp.org/aakp-library/Muscle-weakness/