Polyarteritis nodosa (PAN) can be very serious, but it is very rare – only about one out of every two million people in the UK develop PAN each year. In some cases PAN can be associated with hepatitis B virus infection.
PAN causes inflammation in the medium-sized arteries, particularly those supplying blood to the gut and kidneys. This may only affect part of the wall of the artery, which becomes weak and may bulge, forming an aneurism. If it bursts it can cause serious internal bleeding.
PAN can also involve the whole wall of the artery at a particular point, which causes a blockage.