Risk factors for myelinolysis following correction of severe hyponatremia in the ICU

Myelinolysis (ML) may be related to an excessively rapid correction of hyponatremia, but no study has clearly demonstrated this assumption. We prospectively analyzed the determinants of ML following correction of severe hyponatremia.

Materials and methods

All patients admitted to a 10-bed university medical ICU between July 1995 and March 2003 with hyponatremia (< 120 mmol/l) were included. A cerebral computerised tomography (CT) scan was performed within 2 days, and a cerebral magnetic resonance imaging (MRI) scan was systematically planned at 1 month. ML diagnosis was ascertained when hyperintense lesions were present on the T2 sequence in any area considered normal on the initial imaging. Clinical and biological data were assessed every 6 hours until correction of natremia. Therapeutic options were left to the discretion of the intensivists.

Results

Forty-six patients were elligible (hyponatremia and initial CT scan), 22 were studied (12 refusals, six deaths, five lost, one claustrophoby). MRI-documented ML occured in seven patients (31.8%). Characteristics of patients with and without ML were comparable with regards to age (56 years vs 55 years, P = 0.9), gender, IGS II (34 vs 27, P = 0.17), ICU length of stay (14.5 days vs 7 days, P = 0.19), aetiology of hyponatremia (primary polydipsia 50%, inappropriate ADH secretion 30%, iatrogenic 20%), thyroid dysfunction (0 vs 2), medications before admission (diuretics, angiotensin-converting enzyme inhibitors), Glasgow coma score (13 vs 12, P = 0.65), incidence of mechanical ventilation (2 vs 1, P = 0.2), and occurrence of new neurological symptoms during the ICU stay. No patient died. Six parameters were associated with ML in univariate analysis: chronic use of psychoactive drugs (7 vs 8, P = 0.05), hypertonic NaCl infusion (7 vs 5, P = 0.005), total NaCl intake for ICU day 1 (15.5 ± 12.4 vs 2.8 ± 1.3, P = 0.02), initial kaliemia (3.2 ± 1.1 mM vs 4.1 ± 0.6 mM, P = 0.05), hypokaliemia during correction of natremia (4 vs 1, P = 0.02) and ICU day 1 total water intake (1867 ± 1411 ml vs 804 ± 269 ml, P = 0.013). Neither the correction rate of natremia (0.4 ± 0.23 mM/hour vs 0.53 ± 0.3 mM/hour, P = 0.37) nor plasma osmolality or corrected natremia on admission were associated with occurence of ML

Conclusion

Despite a slow correction rate of hyponatremia, ML remains a frequent (31.8%) complication of severe hyponatremias, especially in case of chronic psychotrope use, initial hypokalemia, and excessive precocious administration of sodium or water.