I received a letter from a reader who recently discovered that a specific test for her kidney function: the GFR - glomerular filtration rate - was abnormal and that her kidneys were only functioning at 50% of their capabilities. She wanted to know if Sjogren's syndrome could be the cause, and if so, what other sjoggies would have to say about their experience with kidney failure and Sjogren's syndrome.
I wrote a post back in 2008 in which I briefly discussed Sjogren's syndrome and kidney (also known as renal) disease in generalities; however this question requires a more thorough answer. As always, I feel more comfortable describing an organ's abnormalities only after we establish some understanding of normalcy. The following sections of simplified information about normal kidney structure and function were found here: (bolding mine).
The kidneys are bean-shaped organs, each about the size of a fist. They are located near the middle of the back, just below the rib cage, one on each side of the spine. The kidneys are sophisticated reprocessing machines. Every day, a person's kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water. The wastes and extra water become urine, which flows to the bladder through tubes called ureters. The bladder stores urine until releasing it through urination.
Wastes in the blood come from the normal breakdown of active tissues, such as muscles, and from food. The body uses food for energy and self-repairs. After the body has taken what it needs from food, wastes are sent to the blood. If the kidneys did not remove them, these wastes would build up in the blood and damage the body.
The actual removal of wastes occurs in tiny units inside the kidneys called nephrons. Each kidney has about a million nephrons. In the nephron, a glomerulus-which is a tiny blood vessel, or capillary-intertwines with a tiny urine-collecting tube called a tubule. The glomerulus acts as a filtering unit, or sieve, and keeps normal proteins and cells in the bloodstream, allowing extra fluid and wastes to pass through. A complicated chemical exchange takes place, as waste materials and water leave the blood and enter the urinary system.
.....In addition to removing wastes, the kidneys release three important hormones:
- erythropoietin, or EPO, which stimulates the bone marrow to make red blood cells
- renin, which regulates blood pressure
- calcitriol, the active form of vitamin D, which helps maintain calcium for bones and for normal chemical balance in the body
For some, Sjogren's syndrome can and does indeed affect the kidneys, however Sjs is not the most frequent cause of kidney failure. The most common causes of kidney disease are diabetes and high blood pressure. People with a family history of any kind of kidney problem are also at risk for kidney disease.
When Sjogren's syndrome related kidney disease does occur, the reporting of incidence varies wildly, read this:
"Renal involvement is reported to occur in 18.4%5 to 67%6 of patients with primary Sjögren's syndrome. This considerable variation is probably due to the different classification criteria used in the studies, as well as the selection of the patients."SS-related kidney disease usually takes one of three forms:
- Damage to the tubule sections of the nephron known as tubular interstitial nephritis, a kidney disorder in which the spaces between the kidney tubules become swollen (inflamed) and damaged. A kidney biopsy of TIN would reveal lymphocytes infiltrating normal surrounding kidney tissue.
- Renal tubular acidosis, in which the kidneys don't properly remove acids in the urine, leaving too much acid in the blood and causing dangerous electrolyte imbalances in the blood.
- Less frequently, damage to the glomerulus also can occur called glomerular disease which causes a loss of blood and protein in the urine and decreases the ability of the kidney to filter waste products.
To diagnose and monitor kidney disease, several laboratory tests are routinely ordered. They may include a urinalysis and other urine tests including:
- Creatinine clearance
- Examination of the urine under a microscope
- Urine for total protein
- Uric acid in the urine
- Urine concentration test
- Urine creatinine
- Urine protein
- Urine RBC
- Urine specific gravity
- Urine osmolality
- Acid loading test (pH)
- Urine calcium
- Urine citric acid
- Urine potassium level
Kidney disease may also cause abnormal results on the following blood tests:
- Anti-glomerular basement membrane antibody test
- Anti-neutrophil cytoplasmic antibodies (ANCAs)
- Anti-nuclear antibodies
- BUN and creatinine
- Complement levels
- Blood potassium
Several other diagnostic tests may be ordered, such as x-rays, abdominal CT scans, IVP (intravenous pyelogram), and kidney biopsy.
Treatment of these and other kidney problems include the use of steroids, immunosuppressive agents, and B cell depletion therapy such as rituximab.
You can read an excellent recent study about SS-related renal disease which goes into much more specific detail here, the conclusion of which includes this:
"...Given the effect of progressive renal disease in patients with pSS, especially those who progress to severe renal impairment before diagnosis, greater emphasis should be placed on screening for renal involvement with a low threshold for early nephrology referral and KB."Well. That's my very, very, long answer to the question of whether Sjogren's syndrome can affect the renal system. The short answer?
Yes. Sjogren's syndrome can cause disease in the kidneys.
But remember: It is not the most common cause of kidney failure. Also know that our kidneys are tough and efficient organs. Damage to some of the kidney does not necessarily translate to overall kidney failure. Read this found here:
Your health care team may talk about the work your kidneys do as renal function. If you have two healthy kidneys, you have 100 percent of your renal function. This is more renal function than you really need. Some people are born with only one kidney, and these people are able to lead normal, healthy lives. Many people donate a kidney for transplantation to a family member or friend. Small declines in renal function do not cause a problem. In fact, you can be healthy with 50 percent of your renal function if it remains stable.The reader is wise to continue this discussion with a nephrologist AND her rheumatologist.
Have you had issues with Sjogren's related kidney disease?