Familial Periodic Paralysis - A Rare Inherited Neurological Disorder.

Introduction

Genes are the basic units of inheritance. Genes contain specific proteins and are responsible for transferring physical and biological traits from parents to their children. Genetic diseases are diseases that are caused by inherited faulty genes from the parents. Familial periodic paralysis is a rare genetic disease. Familial periodic paralysis is a condition that involves extreme muscle weakness and usually begins during childhood or adolescence.

What Is Familial Periodic Paralysis?

Familial periodic paralysis is an inherited neurological disease that is caused due to faults in the genes responsible for balancing sodium and calcium channels in the nerve cells. The people affected by this condition have episodes of severe muscle weakness in which the muscles become loose, decreased in size, and less active. When there is no episode of muscle weakening attack, the affected muscles function normally. Most of the muscle-weakening attacks seen in familial periodic paralysis are temporary, and the inability to move the muscles of the legs and arms returns to normal after a certain period.

What Are the Types of Familial Periodic Paralysis?

There are different types of familial periodic paralysis. The duration and intensity of the muscle-weakness episodes change depending on the type of familial periodic paralysis. There are four main types of familial periodic paralysis. They are:

• Hypokalemic Periodic Paralysis: Hypokalemic periodic paralysis occurs as a result of low potassium levels in the blood. Attacks of muscle weakness may last for a few hours to several days.

• Hyperkalemic Periodic Paralysis: Hyperkalemic periodic paralysis occurs due to high levels of potassium in the blood. Muscle weakness attacks are less severe than hypokalemic periodic paralysis and last for only a short duration of a few minutes to a few hours.

• Thyrotoxic Periodic Paralysis: Thyrotoxic periodic paralysis occurs due to increased thyroid hormone levels in the body. Potassium levels in the blood are mostly low. This type of periodic paralysis is commonly seen in men and can last from several hours to a few days.

• Andersen-Tawil Syndrome: Attacks of muscle weakness are due to the fluctuating levels of potassium in the blood. Attacks can last from certain hours to a few days. Patients affected with Andersen-Tawil syndrome are usually seen to have a particular set of body features. The features include a broad forehead, low-set ears, undersized chin, widely spaced eyes, short stature, and curved fingers (especially the little finger).

Most types of periodic paralysis weaken and affect the skeletal muscles. Skeletal muscles are the muscles that are connected to the bones and help in carrying out the different functions and movements of the body. These muscles fall under the category of voluntary muscles, as an individual can control when and how these muscles would work. The Andersen-Tawil syndrome can attack both skeletal muscles and the heart muscle. Hence, Andersen-Tawil syndrome is the most dangerous form of periodic paralysis.

What Are the Causes of Familial Periodic Paralysis?

Familial periodic paralysis is caused due to a defect in genes that are responsible for providing instructions to make proteins that aid in the movement of skeletal muscles. Every muscle cell has a covering that protects the inner contents of the cell. When a nerve initiates the activation of a muscle cell, a chemical signal is generated, which opens the gate to facilitate the flow of sodium ions into the muscle cell. The entry of a large number of ions changes the electrical charge of the cell, which makes a current wave pass through the muscle fiber. Calcium ions are poured inside the cell and potassium ions are sent out of the cell through the opened potassium channels. The combined action of all the ion channels helps in the activation of muscles. In periodic paralysis, defective genes lead to flaws in the sodium, potassium, and calcium ion channels which in turn disturbs the entire process. Hence, the muscles lose their ability to get activated or relax based on nerve signals leading to periodic paralysis.

What Are the Symptoms of Familial Periodic Paralysis?

The symptoms of the disorder may vary depending on the type of periodic paralysis. However, the general symptoms seen in patients are as follows:

• Severe muscle weakness that may last for a few minutes to a few days.

• Severe muscle pain after exercise.

• Tingling sensation in the body, especially in the legs and arms.

• Muscle cramps.

• Permanent weakness of hip and thigh muscles in the later stages of life.

• Patients with thyrotoxic periodic paralysis may experience sweating, anxiety, weight loss, and abnormal sensation of a heartbeat.

What Are the Trigger Factors of Familial Periodic Paralysis?

The factors which trigger episodes of muscle weakness may vary for each type of periodic paralysis. The common factors are as follows:

• Strenuous exercises.

• Foods with high content of sugar and starch.

• Certain medicines.

• Stress.

• Cold temperatures.

• Fasting.

How to Diagnose Familial Periodic Paralysis?

The different methods employed in the diagnosis of periodic paralysis are as follows:

• The doctor takes a detailed history of the symptoms, family health history, and past health problems of the patient.

• Potassium levels in the patient’s blood are checked during the episode of muscle weakness. The tests reveal abnormal levels of potassium in the blood.

• Blood tests for checking the levels of blood gasses (oxygen and carbon dioxide) and blood minerals like sodium, calcium, magnesium, and copper.

• Electrocardiogram (EEG) is advised to measure the electrical activity of the heart. This is commonly done in patients with Andersen-Tawil Syndrome.

• Genetic testing is done to determine the defects in genes that may run in the family.

• Electromyography is advised, which involves the insertion of a needle electrode into the muscle to measure the electrical activity of the muscle. This test helps to find out the health of the muscles and the nerve cells controlling the muscles.

• Nerve conduction studies are done to find out how fast an electrical signal travels through the nerve to activate a muscle.

• An exercise test is advised. In this test, the patient is made to exercise a single muscle vigorously for about three to five minutes. An electrophysiologic study measures the muscle's weakness before and after the exercise.

How Is Familial Periodic Paralysis Treated?

The main goal of treating familial periodic paralysis is to reduce the severity and number of muscle weakness attacks. The different ways of decreasing the episodes of muscle weakness are as follows:

• In hypokalemic attacks, food rich in carbohydrates (grains, bread, dairy products, cookies, energy drinks, and starchy vegetables like potatoes) should be avoided.

• In severe cases of hypokalemia, intravenous potassium treatments are advised.

• Patients with hyperkalemic periodic paralysis should consume carbohydrate-rich and low-potassium (apples, carrots, cauliflower, rice, bread, and blueberries) foods.

• Patients are advised to avoid strenuous exercises and fasting.

• Patients are advised to take medications that reduce tiredness.

• For patients with Andersen-Tawil syndrome, medicines to improve the functioning of the heart and pacemakers are advised.

• In hyperkalemic periodic paralysis, potassium intake should be reduced through supplements and diet.

• A balanced diet plan advised by a nutritionist depends on the type of periodic paralysis.

Conclusion

Even though familial periodic paralysis is a rare neurological disorder, repeated muscle weakness attacks may lead to permanent weakness. Hence periodic paralysis should be recognized at the earliest to prevent serious complications. Therefore a combined effect of frequent monitoring of blood minerals, controlled diet, medications, and changes in lifestyle helps to manage the symptoms of familial periodic paralysis.