Friday, April 25, 2008

Bilateral diffuse cortical thinning

What that mouthful means is irreversible loss of kidney function. The nephrologist (kidney specialist) says that Kristanne has third-stage Chronic Kidney Disease. Stage 1 is minor loss of function, stage 5 is kidney failure.

At this point, Kristanne has about 50% of the kidney capacity that she needs, which means that her kidneys are overstressed and will continue to suffer damage. The doctor says her kidney function will continue to decline until her kidneys eventually fail, at which point she will need a kidney transplant. It's not something that will happen soon -- it's probably 10 years out, and if she's careful she can stretch it a little more, but barring a miracle of some sort (stem cell therapy is a possibility) she'll eventually need a new kidney.

That's the summary, read on for the details.

The cortex of the kidney is the outer region, and it's the part of the kidney that does the real work of filtering waste products out of the blood. The rest of the kidney is pretty much just plumbing. "Cortical thinning" is just what it sounds like. The cortex has gotten thin, meaning there's much less of the tissue that does the work. "Diffuse" means that it has happened all over the kidney, rather than being localized in one part and "bilateral" means that the cortexes of both kidneys have thinned.

How did this happen? It's not completely clear, but some things are. First, this is not something that has happened in the last few months. The doctor says it takes years of kidney damage to produce this kind of thinning. Second, it's some sort of vascular problem. There are other causes of kidney damage, but they have indicators which aren't present in Kristanne's case, like excessive protein in the urine.

The most likely cause is fibromuscular dysplasia (FMD), which obstructs blood flow to the kidneys. This condition is genetic, which fits with her family history of kidney disease, and it causes both kidney damage and high blood pressure, which fits with the high blood pressure she has had and the kidney damage she now has. The reason obstructed blood flow to the kidneys causes high blood pressure is because the kidneys are the primary regulators of blood pressure. When they see reduced blood flow, they assume that's because the pressure is too low, so they release hormones that cause it to increase.

To determine if FMD is the cause, there are four tests that can be done. The first is an MRI. Unfortunately, the drug administered for the MRI has been found to cause nephrogenic systemic fibrosis in rare cases (about one in three to four thousand), and that condition is fatal. So that test is out. The second is a CT scan, but it also requires the use of a problematic dye. This one isn't fatal, but it does cause kidney damage and loss of kidney function. Not a good idea when kidney function is already poor. So that's also out. The third is an ultrasound, which is inexpensive, harmless, non-invasive and so new that very few radiologists know how to do it. The fourth is surgical, basically to perform an angioplasty on the renal arteries to see if there is a narrowing. Surgery has its own risks, though, and it doesn't always help.

So, the doctor is sending Kristanne to a hospital in Salt Lake to see if maybe there's a radiologist there that knows how to examine the renal arteries and decide if they're narrowed. If so, then he'll recommend the balloon angioplasty or stenting to open up the blood flow.

Even if they can find and fix the original source of the problem, though, Kristanne's kidneys will not repair themselves. Fixing the problem is just part of the overall strategy to slow further damage.

Other parts of the strategy are:

  • Tight control of blood pressure. BP that is too high damages the kidneys, but so does BP that is too low. Kristanne's systolic (higher number) must be kept between 110 and 120.
  • Control of cholesterol. Kristanne's LDL cholesterol is just a tiny bit above the high end of the normal range, but the doctor wants to get it to the low end of the normal range. High cholesterol does kidney damage.
  • Exercise. Regular exercise improves blood flow to the kidney.
  • Weight loss. The work the kidneys have to do is directly proportional to body mass. Reduced body mass means reduced load on the kidneys. If Kristanne's kidney function weren't as bad as it is, she might be able to lose enough weight to where her kidneys could fully handle the job. In that case, assuming good control of blood pressure and cholesterol, they might not deteriorate. They're too far gone for that, they'd be overloaded even if she were dangerously underweight, but reducing the overload will slow the decline.
  • Protein. Protein consumption should be moderate, not too high or too low.
One more question we had was why the kidney damage wasn't detected until now. The doctor says th test most often used to diagnose renal insufficiency is creatinine levels in urine. Unfortunately, although that test is cheap and easy enough to do for everyone during their regular exams, creatinine levels don't rise until kidney function has already dropped below about 70% of necessary. Since healthy people have almost twice the renal capacity they need, that means that over 60% of total kidney function is lost before the problem is noticed. The doctor says that there are some new tests coming out which will do a better job of detecting the problem early yet still be cheap and easy enough to do routinely, but creatinine is the best we've had.

So, that's the scoop. Bad news, but not immediately dangerous. I'm going to be mean and make Kristanne start exercising with me whether she wants to or not. Coincidentally, I've recently started an exercise program that we can do together. Maybe I'll talk about it in another post, but this one is more than long enough.

Kristanne's not sure how she feels about it yet. As for me, I'm just determined to get her to do the things the doctor has suggested to de-stress her kidneys as much as possible and stretch their life.
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