Neurological Disorders: Periodic Paralysis

Introduction

Periodic Paralysis (PP - unofficial abbreviation) is the term used for a type of myopathy (muscle disease), that occurs periodically and belongs to the category of channelopathies.

Channelopathies are a group of diseases resulting from abnormal functioning of ionic channels in the cell membrane. When they occur in the muscles the result is a myopathy, and PP is an example for that. The dysfunction of the channels causes abnormal ionic flow across them and alters the cell functioning.

Types of PP

• Hyperkalemic PP (HyperKPP)
• Hypokalemic PP (HypoKPP)
• Normokalemic PP
• Paramyotonia Congenita

HyperKPP: Here the blood potassium levels are high. This is the result of leakage of potassium from the muscle to the blood.

HypoKPP: Here the blood potassium levels are low. This is the result of leakage of potassium from the blood to the muscle cells.

Normokalemic PP: This is bit controversial diagnosis.

Paramyotonia Congenita: These patients also experience myotonia, and it is paradoxic (so the prefix para) – generally myotonia gets better with activity or exercise and higher temperature but here paradoxically the myotonia worsens with exercise or higher temperature.

Myotonia is the inability to relax a muscle after its contraction. It has several different causes and paramyotonia is just one among those causes.

Clinical Manifestations

Generally there are trigger factors like diet, stress, exercise etc.

Muscle weakness occurs on intermittent basis either triggered by the above factors or sometime spontaneously. The severity and duration varies but almost always patient will recover completely or near completely. The frequency varies.

Severe muscle paralysis especially if involves breathing muscles could be life threatening.

Severe potassium levels, low or high, could affect the functioning of the heart with serious consequences like cardiac arrhythmias.

Hyperthyroidism may be associated with HyperKPP.

Myotonia as described above is seen with paramyotonia.

Diagnosis

The following tests are generally employed;

• Blood potassium levels
• Provocation tests
• EMG (electromyography)
• Thyroid tests
• Genetic tests etc

Treatment

Depending upon the type of PP we are dealing the treatment options include dietary & exercise recommendations, oral or intravenous potassium, acetazolamide, thiazide diuretic etc.

A neurologist is frequently involved in the care of patients with Periodic Paralysis.



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