Polycystic Kidney Disease vs. Acquired Cystic Kidney Disease

Polycystic kidney disease (PKD) is a genetic disease which causes the development of cysts in a patient’s kidneys. It originates from a gene defect in the patient’s deoxyribonucleic acid (DNA) passed on to them by their parent.

The cysts start off very small and grow over many years, even decades. With the most common autosomal-dominant version of the disease, a child of someone with the condition has a 50% chance of inheriting it themselves. Both men and women can develop the disease.

There is more than one type of PKD. The main type is aforementioned autosomal-dominant with faults in genes PKD1 or PKD2, but there is also an autosomal recessive version which is a much rarer disease and caused by an alteration in the gene PKHD1. Nevertheless, the latter is the most common genetic disease for children.

On the other hand, there is only one form of acquired cystic kidney disease (ACKD). The cause of ACKD is not fully known, and contrary to PKD, it tends to develop after a patient has had chronic kidney disease for some time - most commonly when they are undergoing renal dialysis to clean the blood (for example, in end stage renal disease). The cysts are created by the build-up of waste products and the deteriorating filtration in the kidneys.

Structures of the kidneys

The cysts in PKD can cause a kidney to grow to as much as three or four times the kidney’s original size, attaining the size of an apple or an orange. The cysts grow inside the kidney and can take it over, destroying the healthy tissue and reducing the kidney’s ability to function. Subsequently, the disease can trigger chronic kidney disease.

The situation is somewhat different for ACKD, as the affected kidneys tend to stay around their original size and occasionally become smaller. Still, it must be noted that in some instances uncommon macroscopic features hamper adequate differential diagnosis in the clinical setting.

Dominant symptoms

An individual with PKD can exhibit a number of different symptoms. They may develop lumps on one or both sides of their abdomen due to the size of the kidneys. The disease can cause high blood pressure as well. Other symptoms can include blood in the urine as a result of the cysts that puncture in the kidney and patients can suffer from kidney stones. Pain is a factor too, usually from the cysts expanding its structure, but also  a feeling of the stomach being full due to the larger than average size of their renal organs. The patient can also experience joint pain.

In comparison, ACKD does not show any major symptoms. The patient does not feel any pain from the developing disease or develop blood pressure. The main problem that may occur is when a cyst punctures, resulting in pain or blood in the urine.

How many develop the disease?

PKD is the fourth most common form of kidney failure in the USA. The most common form of PKD, autosomal dominant polycystic kidney disease, affects about 1 in 500 people in the US. The less common version of PKD, autosomal recessive polycystic kidney disease affects about 1 in 200,000 people.

With ACKD, only people who have reached the latter stages of kidney disease develop it. Around 7 – 22% of people prior to dialysis get it. Then about 44% develop it within 3 years of beginning dialysis. This rises to 79% for more than three years and reaches 90% for longer than eight years.

Treatment options

There is no treatment for PKD but the symptoms, such as high blood pressure and the kidney stones that can develop, can be treated.  Recent breakthroughs in genetics have the potential to target the precise mechanisms of cyst formation and expansion, leading to novel therapies in PKD.

ACKD is fairly asymptomatic so there is usually no treatment for any particular symptoms. There is also no treatment for the condition itself. Mild bleeding episodes with pain that arise due to puncture of a cyst are usually treated with analgesics.