Sarcoidosis is a rare inflammatory disease that can affect different tissues and organs. The disease is characterized by the formation of granulomas, small clumps of immune cells that can form anywhere in the body. When these granulomas form in the kidney, the condition is called renal sarcoidosis.
What is renal sarcoidosis?
Renal sarcoidosis is thought to occur in about 35 to 50 percent of sarcoidosis patients. If left untreated, it can lead to kidney failure.
Hypercalcemia, or high levels of calcium in the blood, are seen in 10–17 percent of patients with sarcoidosis, and hypercalciuria —high levels of calcium in the urine — in 40–62 percent of patients. This increase in calcium can contribute to the formation of kidney stones.
The granulomas formed in sarcoidosis produce an enzyme called 1-alpha-hydroxylase. This enzyme increases the production of vitamin D by the body. Vitamin D stimulates the intestines to absorb calcium, and causes the kidneys to reabsorb calcium instead of releasing it as waste in the urine. The combination of these factors can result in higher-than-usual calcium levels in the blood. Because there is more calcium in the blood, more calcium is present in the urine as well.
High levels of calcium in the blood also cause blood vessels in the kidney to constrict, preventing proper clearance of waste from the blood and leading to dehydration. The combination of these factors set up the right conditions for the development of kidney stones, which can further obstruct the kidneys. In rare cases, inflammation and calcium buildup in the channels of the kidney can lead to kidney failure.
Renal sarcoidosis is usually accompanied by systemic sarcoidosis, and can be an early sign of more general disease. However, it can also occur on its own.
Symptoms of renal sarcoidosis
Symptoms of kidney problems caused by sarcoidosis may include:
- dehydration
- inflammation
- formation of kidney stones
Diagnosis of renal sarcoidosis
The diagnosis of renal sarcoidosis is usually made by discarding other kidney disorders, with a definitive diagnosis usually following a biopsy. A biopsy involves the surgical removal of a small piece of tissue, which is then examined under a microscope to look for sarcoidosis granulomas.
Measurements of calcium in the urine can also be used to diagnose this disease, or help in reaching a diagnosis.
Treatment of renal sarcoidosis
Intravenous (IV) fluids may be prescribed to treat dehydration.
Corticosteroids such as prednisone are the first choice of treatment, as they reduce the number and activity of granulomas, ease inflammation, and block the activity of 1-alpha-hydroxylase to reduce the absorption of calcium.
Preventive measures, such as a low dietary intake of calcium and vitamin D, as well as limiting exposure to sunlight, are also recommended.
Immunosuppressants such as azathioprine may be prescribed to reduce granuloma number and activity. Some immunosuppressant treatments commonly prescribed to treat pulmonary sarcoidosis, such as methotrexate, may not be suitable for renal sarcoidosis as they can have toxic effects on the kidneys.
Kidney failure secondary to sarcoidosis is relatively uncommon, but it can happen. Patients may placed temporarily on dialysis, in which a machine filters waste from the blood. In extreme cases, a kidney transplant may be necessary.
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