Enteritis and colitis associated with mefenamic acid.

Water intoxication causes hyponatraemia, which is responsible for the neurological dysfunction by causing intracellular overhydration. Symptoms may occur if the serum sodium concentration is less than 120 mmol/l, but the degree of brain dysfunction corresponds with the rapidity of development of the hyponatraemia. Intracellular potassium concentration is reduced, partly due to increased intracellular water and partly due to loss of intracellular potassium, but it is not clear whether cellular swelling alone or the potassium deficit is responsible for the encephalopathy. The accompanying brain oedema is usually transient but the intracranial hypertension may be catastrophic, causing uncal and tonsillar herniation.' The intracranial pressure later reverts to normal.2 In our patient signs developed with such rapidity that therapeutic measures succeeded in reducing the intracranial pressure only after irreversible brain stem damage had taken place.