Overview Periodic paralyses

The ability we have to control and move the muscles in our body depends upon the passage of electrical signals along the nerves and into our muscles. The periodic paralyses are conditions in which the muscles which control body movements (known as skeletal muscles) have a disturbance in their normal ability to allow the passage of these electrical signals.

In the past classification was based upon changes in the level of blood potassium (which is normally between 3.5 and 5.1 mmol per litre) during, and particularly at the onset of, the attack.

The three types in this classification are:

Hypokalaemic periodic paralysis: In these attacks the blood potassium is low

Hyperkalaemic periodic paralysis: In these attacks the blood potassium is high

Normokalaemic periodic paralysis: In these attacks the blood potassium remains normal

In fact, it has recently been discovered that it is not the change in the blood potassium level that is the primary problem in periodic paralysis. The primary problem in all of these conditions is that the normal pores which exist in the walls of the muscle cells don’t work properly.

It does seem that changes in blood potassium levels can further hinder the function of these pores and that is why changes in blood potassium can be relevant. However, other factors separate from blood potassium can also worsen the function of the pores, so a change in blood potassium is not essential.