Extreme Hyponatremia Complicated by Osmotic Demyelination in a Previously Healthy Young Individual

RATIONALE: Severe hyponatremia can lead to dramatic complications whether it is treated or not. At times, it may be very severe (serum Na concentration: Na(S) < 115 mmol/L) or even extreme (Na(S) < 105 mmol/L)(a) and its cause difficult to identify, especially in younger individuals with no history of water disorders. The case presented herein illustrates these points quite eloquently and leads us to believe that the current recommendations for the treatment of very severe hyponatremia require some fine-tuning. PRESENTING CONCERNS: A 26-year-old man was admitted to our intensive care unit for a Na(S) of 88 mmol/L in the absence of obvious extracellular fluid volume contraction. He had been experiencing vomiting, diarrhea, fatigue, and excessive thirst for the past 6 weeks and minor neurological symptoms just before admission. Laboratory tests at presentation also showed a urine osmolarity of 697 mOsm/L and urine Na of 40 mmol/L. DIAGNOSES: The presenting concerns were consistent with syndrome of inappropriate antidiuretic hormone secretion (SIADH) manifesting as extreme, yet mildly symptomatic hyponatremia. At the same time, they did not point toward a specific cause initially. INTERVENTIONS: The patient was treated through water restriction, subcutaneous desmopressin, and various intravenous (IV) fluids. Our goal had been to increase Na(S) at a rate of 4 to 6 mmol/L/day and required the amount of NaCl and free water perfused hourly to be readjusted constantly. Access to water also had to be opposed as the patient was unable to tolerate his thirst. OUTCOMES: During the first 6 days, the rate of Na(S) correction achieved was ~6 mmol/L/day. The patient improved initially but at the end of day 6, he experienced severe extrapontine osmotic demyelination (with widespread pyramidal and extrapyramidal deficits) that did not respond to intravenous immunoglobulin and Na(S) relowering. A little more than 3 weeks later, he began to develop low blood pressure and a subfebrile state that revealed secondary to severe Addison disease. The water disorder and insatiable thirst subsided gradually upon replacing the deficient hormones but the neurological disorder went on to become permanent and highly disabling. TEACHING POINTS: (1) Very severe hyponatremia should always be handled as an emergency and monitored stringently in view of its potential to cause irreparable damage. (2) Because it is a major risk factor for osmotic demyelination, it should probably be corrected at a rate of less than 4 mmol/L/day especially if it is in the extreme range, chronic, or of unknown duration. (3) It can be a presenting manifestation of Addison disease.