Autosomal dominant polycystic kidney disease is a relatively common (prevalence 1 in 1,000) and important cause of CKD. Eighty-five percent of cases are caused by mutations of the PKD1 gene with the remaining 15 % of cases due to mutations of the PKD2 gene. These mutations cause defective cell signalling which leads to cyst formation. Small cysts develop in childhood but may not be detectable until early adult life.

Most patients with ADPKD have no symptoms. Some experience loin discomfort and others a fullness in their abdomen. When acute pain occurs this is likely to be due to haemorrhage or infection in a cyst. ADPKD may also come to light during investigation of hypertension, chronic kidney disease or subarachnoid haemorrhage. Although polycystic kidneys are the commonest cause of renal masses that find their way into clinical examinations, some are easier to feel than others which means that on occasion only one and sometimes neither kidney is palpable.

The most important are erythrocytosis, hepatic cyst formation and intracranial aneurysms. Erythrocytosis occurs because the cysts produce erythropoietin. It is usually inferred because patients with polycystic kidney disease are generally less anaemic than you would expect for a given level of renal failure. Hepatic cysts can cause hepatomegaly which may be quite striking, though liver failure is rare. Intracranial aneurysms are said to occur in around 10 % of patients with polycystic kidneys and may bleed causing subarachnoid haemorrhage.

If a patient has a family history of polycystic kidneys, palpable masses in both loins and enlarged kidneys containing multiple cysts on renal ultrasound then the diagnosis is very easy and obvious. Difficulties may arise if there is no family history (possible new mutation), kidneys that are difficult to feel (not uncommon) or an ultrasound report which mentions only a few cysts and does not specify the renal size. Ultrasonic criteria for ADPKD are in fact quite well defined. In a patient with a positive family history then a diagnosis of ADPKD is likely if the kidneys are enlarged (>12 cm) with two or more cysts in one or both kidneys by the age of 30, two or more bilaterally by age 59 and four or more cysts in both kidneys from age 60 onwards (Fig. 26.1).