What is medullary cystic kidney disease?
Medullary cystic kidney disease (MCKD) is a rare condition in which small, fluid-filled sacs called cysts form in the center of the kidneys. Scarring also occurs in the tubules of the kidneys. Urine travels in the tubules from the kidney and through the urinary system. The scarring causes these tubules to malfunction.
In order to understand MCKD, it helps to know a little bit about your kidneys and what they do. Your kidneys are two bean-shaped organs about the size of a closed fist. They’re located on either side of your spine, near the middle of your back.
Your kidneys filter and clean your blood — every day, about 200 quarts of blood pass through your kidneys. The clean blood returns to your circulatory system. Waste products and extra fluid become urine. The urine is sent to the bladder and eventually removed from your body.
The damage caused by MCKD leads the kidneys to produce urine that isn’t concentrated enough. In other words, your urine is too watery and lacks the proper amount of waste. As a result, you’ll end up urinating way more fluid than normal (polyuria) as your body tries to get rid of all the extra waste. And when the kidneys produce too much urine, then water, sodium, and other vital chemicals are lost.
Over time, MCKD can lead to kidney failure.
Juvenile nephronophthisis (NPH) and MCKD are very closely related. Both conditions are caused by the same type of kidney damage and result in the same symptoms.
The major difference is the age of onset. NPH usually occurs between ages 10 to 20, while MCKD is an adult-onset disease.
In addition, there are two subsets of MCKD: type 2 (typically affects adults ages 30 to 35) and type 1 (typically affects adults ages 60 to 65).
Both NPH and MCKD are autosomal dominant genetic conditions. This means you only need to get the gene from one parent to develop the disorder. If a parent has the gene, a child has a 50 percent chance of getting it and developing the condition.
Besides age of onset, the other major difference between NPH and MCKD is that they’re caused by different genetic defects.
While we focus on MCKD here, much of what we discuss is applicable to NPH as well.
The symptoms of MCKD look like the symptoms of many other conditions, making it difficult to make a diagnosis. These symptoms include:
- excessive urination
- increased frequency of urination at night (nocturia)
- low blood pressure
- salt cravings (due to excess sodium loss from the increased urination)
- bruising or bleeding
- easily fatigued
- frequent hiccups
- changes in skin color (yellow or brown)
- itching of the skin
- muscle cramping or twitching
- loss of feeling in the hands or feet
- vomiting blood
- bloody stools
- weight loss
- changes in mental state (confusion or altered alertness)
If you have symptoms of MCKD, your doctor may order a number of different tests to confirm your diagnosis. Blood and urine tests will be the most important for identifying MCKD.
Complete blood count
Blood urea nitrogen (BUN) testing looks for the amount of urea, a breakdown product of protein, which is elevated when kidneys aren’t functioning properly.
A 24-hour urine collection will confirm excessive urination, document the volume and the loss of electrolytes, and measure the creatinine clearance. The creatinine clearance will reveal whether the kidneys are functioning properly.
Blood creatinine test
A blood creatinine test will be done to check your creatinine level. Creatinine is a chemical waste product produced by the muscles, which is filtered out of the body by your kidneys. This is used to compare the level of blood creatinine with kidney creatinine clearance.
Uric acid test
A uric acid test will be done to check uric acid levels. Uric acid is a chemical created when your body breaks down certain food substances. Uric acid passes out of the body through urine. Levels of uric acid are usually high in people who have MCKD.
A urinalysis will be done to analyze the color, specific gravity, and pH (acid or alkaline) levels of your urine. In addition, your urine sediment will be checked for blood, protein, and cell content. This testing will assist the doctor in confirming a diagnosis or ruling out other possible disorders.
In addition to blood and urine tests, your doctor may also order an abdominal/kidney CT scan. This test uses X-ray imaging to see the kidneys and inside of the abdomen. This can help rule out other potential causes of your symptoms.
Your doctor may also want to perform a kidney ultrasound to visualize the cysts on your kidneys. This is to determine the extent of kidney damage.
In a kidney biopsy, a doctor or other health professional will remove a small piece of kidney tissue to examine it in a lab, under a microscope. This can help rule out other possible causes of your symptoms, including infections, unusual deposits, or scarring.
A biopsy can also help your doctor determine the stage of the kidney disease.
There is no cure for MCKD. Treatment for the condition consists of interventions that attempt to reduce symptoms and slow the progression of the disease.
In the early stages of the disease, your doctor may recommend increasing your intake of fluids. You may also be required to take a salt supplement to avoid dehydration.
As the disease progresses, kidney failure can result. When this occurs, you may be required to undergo dialysis. Dialysis is a process in which a machine removes wastes from the body that the kidneys can no longer filter out.
Although dialysis is a life-sustaining treatment, people with kidney failure may also be able to undergo a kidney transplant.
The complications of MCKD can affect various organs and systems. These include:
- anemia (low iron in the blood)
- weakening of the bones, leading to fractures
- compression of the heart due to fluid buildup (cardiac tamponade)
- changes in sugar metabolism
- congestive heart failure
- kidney failure
- ulcers in the stomach and intestines
- excessive bleeding
- high blood pressure
- menstrual problems
- nerve damage
MCKD leads to end-stage renal disease — in other words kidney failure will occur eventually. At that point, you will need to have a kidney transplant or undergo dialysis regularly in order to keep your body functioning properly. Talk to your doctor about your options.