Periodic paralysis is a group of heterogeneous muscular pathologies. They are characterized by episodes of weakness and muscle paralysis, affecting mostly the limbs. The episodes have a variable life, but often last very little and occur at irregular intervals. This helps to make the diagnosis difficult.

In most cases, periodic paralysis is hereditary conditions. They are dominant autosomal transmissible diseases: just one parent has the mutated gene, to have 50% probability of transmission. Who inherits the mutated gene has muscles vulnerable to changes in potassium levels in the blood. Depending on whether the potassium is too much or too little, it is referred to hypocalemic or hypercaliemic paralysis.

The first symptoms of periodic paralysis appear during childhood or adolescence. They occur mainly when awakened, or after resting. Alternatively, they are manifested by intense physical efforts or the consumption of carbohydrate-rich foods. They are also related to the consumption of alcohol and excess salt.

Symptoms may vary considerably, depending on the condition of the patient. Generally, these include weakness or paralysis of the muscles of the hips, shoulders, legs, arms. Episodes can last between 3 and 23 hours, too little time to ensure a safe diagnosis. Genetic tests are essential to give a clear answer. In case of recurrent family episodes, prenatal diagnosis may also be considered.