POLYCYSTIC KIDNEY DISEASE - a patient's guide
What is it?
Autosomal dominant polycystic kidney disease (ADPKD) affects about one person per thousand and accounts for 5-10 percent of patients commencing dialysis with end stage renal disease. Less than one percent of nephrons are affected. The kidneys steadily increase in size and most people enter end stage renal failure in the 4th to 6th decade of life. Some patients are completely unaware of their disorder until a chance discovery in later life and never require dialysis therapy. About 40 percent of patients are unable to give a family history consistent with polycystic kidney disease suggesting the possibility of a high spontaneous mutation rate.
What are the symptoms?
Pain is the most common symptom and may be unilateral or bilateral, a vague sense of heaviness, or a dull aching to knife-like and stabbing loin pain. The pain may be related to blood vessel rupture with haemorrhage into a cyst or around a cyst. When the pain is persistent the possibility of infection, kidney stones, or tumours must be considered.
Other modes of presentation include blood in the urine, urinary tract infection which may be difficult both to diagnose and treat, or the passage of urinary stones. Hypertension develops in more than half of patients at some time in the course of the disease. It often develops in more than half of patients at some time in the course of the disease. It often precedes measurable change in renal function by several years. Hypertension is one of the most important risk factors for progression of rental insufficiency as well as contributing to overall cardiovascular deaths.
Cerebral aneurysms are found with increased frequency in ADPKD patients, with an overall prevalence of about 5 percent. Recent data suggests that 12 percent of all affected patients die from a neurological event, six percent of them with a subarachnoid haemorrhage. About 6 percent of patients presenting with berry aneurysms have associated polycystic kidney disease.
Both kidneys are abnormal, although one of the pair may be considerably larger than the other. Kidneys are usually diffusely cystic and commonly have lengths ranging from 15-20cm. Massive proteinuria is rare. Ultrasonography is the most cost effective method of screening for ADPKD. A diagnosis can be established in virtually all patients older than 30 years. In individuals younger than 30, a positive diagnosis by ultrasound is estimated to be 22 percent, 66 percent, and 85 percent, in ages five, 15 and 25 years respectively.
In other words the probability of having ADKPD after normal ultrasound test results in patients who have 1st degree relatives with the diagnosis is 46 percent, 28 percent and 14 percent for people in their 1st, 2nd and 3rd decades respectively. It is recommended that screening take place over the age of 20 and if negative be repeated over the age of 30 if concern remains. Recent data shows that there is an increase in the left ventricular mass index already evident in affected adolescents and because of this finding all children of affected families should have their blood pressure and renal function checked at regular intervals, every 2-5 years, to allow intervention. A case can be put against screening because of the clear negative implications which arise in relationship to insurance ratings and job applications for affected individuals. While genetic testing for PKD1 and 2 genes has not yet entered current clinical practice, it is possible, and this possibility raises further ethical issues.
What can be done to help?
It is currently recommended that those who have a positive family history of cerebral aneurysms or who themselves have had a history of previous aneurysm rupture should be screened with either high resolution CT scan or magnetic resonance angiography (MRI). It is uncommon for aneurysms under 10mm in diameter to rupture and thus over this size should be considered for surgery. It is not recommended that others be screened routinely for berry aneurysms.
Pain episodes often associated with haematuria last a few days to weeks and resolve spontaneously. They are usually managed with simple analgesia. Sometimes chronic pain can be relieved by cyst aspiration or surgical decompression.
One or more cysts may become infected and like any deep seated infection the condition may be difficult to treat. Some cysts are only accessible to lipid soluble antibiotics which include Ciprofloxacin, Erythromycin and Trimethoprin Sulphamethoxazole. Ordinarily, a course of antibiotics should be prolonged for 7-10 days when renal infection is being treated.
The frequency of renal stone formation is approximately 20 percent and stones are most frequently composed of uric acid or calcium oxalate. Standard treatment for renal stone disease is utilised.
Effective treatment of hypertension may have a dual benefit: slowing the rate of decline in kidney function, and minimising the risk of rupture of a cerebral aneurysm. Patients with hypertension are much more likely to develop aggressive renal failure. The aim of antihypertensive therapy in these patients would be to lower the blood pressure to 130-140/80-85.
This is not necessary for this group of patients.
Cysts in other organs
There is a 50 to 75 percent incidence of liver cysts and cysts are found commonly in a variety of other organs. Liver dysfunction and portal hypertension is rarely seen in these patients. The situation is quite different from that seen in children with autosomal recessive polycystic kidney disease, a much rarer disease where there is usually liver involvement with congenital hepatic fibrosis.
Renal replacement therapy
Both peritoneal and haemodialysis modalities of dialysis have been successfully used to treat patients with end stage ADPKD and kidney transplant is also routinely used in their management. Post transplant survival rates appear to be equal to those of patients with other kidney disorders.