72. Disorders in sodium, potassium and magnesium metabolism - etiology, pathogenesis, clinical manifestations.

Disorders in sodium, potassium, and magnesium metabolism – etiology, pathogenesis, and clinical manifestations.

Sodium metabolism disorders

Hyponatremia (Na <135 mmol/L)

Etiology

• Hypovolemic hyponatremia: diarrhea, vomiting, diuretics, burns.
• Euvolemic hyponatremia: SIADH, hypothyroidism, adrenal insufficiency.
• Hypervolemic hyponatremia: heart failure, cirrhosis, nephrotic syndrome.

Pathogenesis

• Dilutional (excess water relative to sodium).
• Sodium loss exceeding water loss.

Clinical manifestations

• Headache, nausea, vomiting.
• Muscle cramps.
• Confusion, lethargy.
• Seizures, coma (severe cases).

Hypernatremia (Na >145 mmol/L)

Etiology

• Water loss (dehydration): fever, sweating, diarrhea.
• Diabetes insipidus (central or nephrogenic).
• Excessive sodium intake (rare).

Pathogenesis

• Cellular dehydration due to hyperosmolarity → water shifts from cells to ECF.

Clinical manifestations

• Thirst.
• Weakness, irritability.
• Neurological signs: confusion, seizures, coma.

Potassium metabolism disorders

Hypokalemia (K <3.5 mmol/L)

Etiology

• GI losses: vomiting, diarrhea.
• Renal losses: hyperaldosteronism, diuretics.
• Shift into cells: insulin excess, alkalosis.

Pathogenesis

• Reduced extracellular K → hyperpolarization of cell membranes → decreased excitability.

Clinical manifestations

• Muscle weakness, fatigue.
• Hyporeflexia, cramps.
• Cardiac arrhythmias (flattened T waves, U waves).
• Constipation, ileus.

Hyperkalemia (K >5.5 mmol/L)

Etiology

• Renal failure (most common).
• Hypoaldosteronism (Addison’s).
• Cell lysis (hemolysis, rhabdomyolysis, tumor lysis).
• Acidosis (shift from cells to plasma).

Pathogenesis

• Depolarization of cell membranes → increased excitability initially, then reduced as levels rise further.

Clinical manifestations

• Muscle weakness, paralysis.
• Cardiac arrhythmias (peaked T waves, widened QRS, sine-wave pattern).
• Paresthesias.

Magnesium metabolism disorders

Hypomagnesemia (Mg² <0.7 mmol/L)

Etiology

• Malnutrition, alcoholism.
• Diarrhea, malabsorption.
• Diuretics.

Pathogenesis

• Mg² deficiency → impaired PTH secretion and action → secondary hypocalcemia.
• Affects K handling → often associated with hypokalemia.

Clinical manifestations

• Neuromuscular: tremor, tetany, muscle weakness, hyperreflexia.
• CNS: confusion, seizures.
• Cardiac: arrhythmias (similar to hypokalemia).

Hypermagnesemia (Mg² >1.1 mmol/L)

Etiology

• Renal failure.
• Excessive intake (antacids, laxatives containing Mg² ).

Pathogenesis

• Depresses neuromuscular and cardiac conduction.

Clinical manifestations

• Lethargy, weakness.
• Hyporeflexia.
• Hypotension, bradycardia.
• Severe: respiratory paralysis, cardiac arrest.

Summary Table