Our ability to control and move the muscles in our body depends on the passage of electrical signals along the nerves and into our muscles. Periodic paralyses are a group of conditions in which the muscles - skeletal muscles - that control body movements are not able to pass on electrical signals as normal.

People with periodic paralysis experience intermittent (periodic) attacks of muscle weakness (paralysis). The extent to which a person is affected varies. Muscle weakness may be confined to the forearm and hand muscles, resulting in a weak grip, or weakness may be generalised, involving the arms and legs. In the most severe cases this may result in an complete inability to move. It is rare for the breathing, speaking or swallowing muscles to be affected. The heart muscle is only involved in an uncommon form of periodic paralysis called Andersen's syndrome.

There are three types of periodic paralysis:

  • Hypokalaemic periodic paralysis
  • Hypokalaemic periodic paralysis
  • Normokalaemic periodic paralysis

The primary problem in all of these conditions is that the normal pores (ion channels) in the walls of the muscle cells don't work properly. This means that the highly regulated passage of ions (best thought of as small salt particles) into and out of the muscles cells is interrupted and consequently so are the electrical signals required for muscle contraction.

All types of periodic paralysis are genetic. They are inherited in an autosomal dominant pattern.

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