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. These cysts scar the kidneys and cause them 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 is not concentrated enough. In other words, your urine is essentially 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.
Types of MCKD
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 30-35) and type 1 (typically affects adults 60-65).
Causes of MCKD
Both NPH and MCKD are autosomal dominant genetic conditions. This means that 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 this article focuses on MCKD, much of what is discussed is applicable to NPH as well.
Symptoms of MCKD
Unfortunately, the symptoms of MCKD look like the symptoms of many other conditions, making it difficult to make a diagnosis. These symptoms include:
- excessive urination (medically known as polyuria)
- increased frequency of urination at night
- low blood pressure
- salt cravings (due to excess sodium loss from the increased urination)
As the disease progresses, kidney failure (also known as end-stage renal disease) may result. Symptoms of kidney failure can include the following:
- 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 and/or feet
- vomiting blood
- bloody stools
- weight loss
- changes in mental state (confusion or altered alertness)
Testing for and Diagnosing MCKD
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. These tests are outlined below.
Complete Blood Count
A complete blood count looks at your overall numbers of red blood cells, white blood cells, and platelets. This test looks for anemia and signs of infection.
Blood urea nitrogen (BUN) testing looks for the amount of urea, a breakdown product of protein, which is elevated when kidneys are not 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 patients that 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 these 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 understand the stage of the kidney disease.
How Is MCKD Treated?
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 may 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, patients with kidney failure may also be able to undergo a kidney transplant.
Long-Term Complications of MCKD
The complications of MCKD can impact various organs and systems. Complications 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
What Is the Outlook for MCKD?
Unfortunately, MKCD leads to end-stage renal disease — in other words, eventually, kidney failure will occur. 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.