bubble_chart Overview

Periodic paralysis is a group of diseases characterized by recurrent episodes of flaccid paralysis in the skeletal muscles of the limbs. It includes three types: hypokalemic, hyperkalemic, and normokalemic. The hypokalemic type is the most common (this section describes this type).

bubble_chart Etiology

Hypokalemic periodic paralysis is an autosomal dominant genetic disorder. In foreign countries, it often has a family history, hence termed familial periodic paralysis, whereas in China, sporadic cases are more common.

During an episode of this disease, the concentration of potassium ions inside and outside cells changes, increasing intracellularly and decreasing extracellularly and in the serum. This shift in concentration leads to a hyperpolarized state of the muscle membrane potential, blocking sodium ion channels on the membrane, thereby causing neuromuscular transmission failure and unresponsiveness to electrical stimulation. Therefore, this condition often occurs during rest after a heavy meal or after intense exercise, as glucose entering liver and muscle cells for glycogen synthesis carries potassium ions with it, reducing extracellular and serum potassium levels, which aligns with the hypokalemia observed during episodes. Injecting glucose to induce this disease follows the same mechanism.

Additionally, in China, some hyperthyroid patients also experience hypokalemic periodic paralysis, with episodes decreasing or ceasing as hyperthyroidism is controlled. The pathogenic mechanism during episodes is the same as described above.

bubble_chart Pathological Changes

Muscle biopsy under light microscopy reveals vacuolar degeneration of muscle fibers, with focal necrosis in advanced stages; muscle fibers vary in size, and connective tissue is increased. Electron microscopy shows localized dilation of sarcoplasmic reticulum tubules containing glycogen and carbohydrates. Intramuscular potassium and water content are elevated.

bubble_chart Clinical Manifestations

The disease often begins in adolescence, with males being more affected than females. Common triggers include heavy meals, intense physical activity, cold exposure, and emotional stress. Acute onset typically occurs at night, with the main symptom being paralysis of the limbs and trunk. The classic paralysis starts in the lower limbs and ascends to the upper limbs and neck muscles, presenting bilaterally and symmetrically, with proximal muscles more severely affected than distal ones. Generally, muscles innervated by cranial nerves and respiratory muscles are spared, though in rare cases, respiratory muscle paralysis and cardiac arrhythmias may occur. Examination reveals flaccid paralysis, diminished or absent tendon reflexes, clear consciousness, and intact sensation. Symptoms resolve spontaneously within hours or days without sequelae. Recurrent episodes are common but tend to decrease or even cease after middle age.

bubble_chart Auxiliary Examination

1. Serum potassium grade I decreased.
2. The electrocardiogram showed hypokalemic changes, including prominent U waves, flattened T waves, prolonged QT interval, and widened QRS complexes.
3. Electromyography revealed increased excitation threshold, and even disappearance of electrical stimulation response.

bubble_chart Diagnosis

1. Acute onset, with flaccid limb paralysis occurring under predisposing factors such as heavy meals or strenuous exercise, without impairment of consciousness, sensory disturbances, or sphincter dysfunction.
2. History of recurrent episodes or family history.
3. Serum potassium is decreased, and electrocardiogram shows hypokalemic changes.

bubble_chart Treatment Measures

During episodes of hypokalemia, take 5-15g of potassium chloride or 30ml of 10% potassium chloride solution per hour until improvement, avoiding hypertonic glucose injections. For hyperkalemia, intravenous calcium gluconate or oral glucose (2g/kg) can be administered. In severe cases, intravenous glucose infusion is recommended.

bubble_chart Prevention

1. Conduct proper publicity and explanation to make patients understand the mechanism of disease and predisposing factors, so as to cooperate in prevention.
2. It is advisable to eat small, frequent meals with a low-salt and low-sugar diet. Avoid predisposing factors such as overeating, excessive fatigue, and exposure to cold.
3. For those with frequent attacks, acetazolamide (Diamox) 250mg can be taken four times daily during the intermission period, or spironolactone 20–40mg three times daily.
4. For suspected hyperthyroidism patients, serum free thyroxine (T4) and protein-bound iodine tests should be performed to promptly treat hyperthyroidism and prevent attacks.

bubble_chart Differentiation

1. Secondary hypokalemic paralysis, such as that caused by primary aldosteronism, renal tubular acidosis, diabetes, vomiting, diarrhea, etc., has a history and signs of the primary disease, which can aid in differentiation.
2. Acute infectious polyneuritis, in addition to limb paralysis, often involves cranial nerve damage and cerebrospinal fluid protein-cell dissociation, with a longer disease course.
3. Acute myelitis presents with complete sensory, motor, and autonomic nerve dysfunction below the level of the lesion, making it easy to differentiate.
4. Hysterical paralysis has obvious psychological factors, normal serum potassium and electrocardiogram, and responds well to suggestive therapy.