Familial periodic paralyses are a group of inherited neurological disorders caused by mutations in genes that regulate sodium and calcium channels in nerve cells.
They are characterized by episodes in which the affected muscles become slack, weak, and unable to contract. Between attacks, the affected muscles usually work as normal.
Periodic paralysis is an autosomal dominant myopathy, meaning only one parent needs to carry the gene mutation to affect the children. However, not all family members who share the gene are affected to the same degree.
The two most common types of periodic paralyses are:
Hypokalemic periodic paralysis - characterized by a fall in potassium levels in the blood. In individuals with this mutation attacks often begin in adolescence and are triggered by strenuous exercise or high carbohydrate meals. Weakness may be mild and limited to certain muscle groups, or more severe and affect the arms and legs. Attacks may last for a few hours or persist for several days. Some patients may develop chronic muscle weakness later in life.
Hyperkalemic periodic paralysis - characterized by a rise in potassium levels in the blood. Attacks often begin in infancy or early childhood and are precipitated by rest after exercise or by fasting. Attacks are usually shorter, more frequent, and less severe than the hypokalemic form. Muscle spasms are common.
Treatment of the periodic paralyses focuses on preventing further attacks and relieving acute symptoms.
Hypokalemic attacks may be prevented by:
Hyperkalemic attacks can be managed by:
The prognosis for the familial periodic paralyses varies. Chronic attacks may result in progressive weakness that persists between attacks. Some cases respond well to treatment, which can prevent or reverse progressive muscle weakness.