Does hyponatraemia influence visual memory and executive functions in schizophrenia psychosis? Review and selective preliminary report

Abstract

Introduction: Increased thirst and electrolyte disturbances feature up to 20% inpatients with schizophrenia with bad
course of disease and cognitive deficits, with worsening in compliance and restricted fluid ingestion. Executive dysfunctions
co-occur with hyponatraemia, making complex plan of activity difficult and increasing the risk of falls in elderly.
Inter-connections between executive deficits and memory systems are highly suspected.
Aim of the study was to prolonge impact of hyponatraemia during admission on visual memory tests’ results during
one-week-before-discharge period, after serum sodium normalization.
Material and methods: Emergency psychiatric wards’ inpatients with ICD-10 F2x schizophrenic psychosis without serious
somatic co-morbidity, without lithium and diuretics. Experimental group n = 11 with mild euvolemic hyponatraemia
during 0–5 days after admission (serum sodium < 135 mmol/l, median 133.6 mmol/l, 15% of all F2x-hyponatraemia
group); control group n = 22 with normonatraemia (135–145 mmol/l); age 47 vs 39y (p = 0.05), female 64%, duration
of ilness 17 vs 11y (p = 0.032), number of hospitalizations 29 vs 11 (p = 0.1), polydipsia 64 vs 41%, equal antipsychotic
dose equivalents. Natraemia normalization in 0–6 days (46%), 7–28 days (18%) or more than 28 days (27%).
One-time visual memory evaluation with Benton (BVRT) & complex Rey figure (CROFT) tests along to general cognitive
assesment with MMSE in experimental and control groups, in stable symptomatic phase. Comparisons between total
groups and in 11 pairs matched by gender, age, diagnosis and duration of ilness. T- or U Mann-Whitney tests and Pearson
correlation indexes, p < 0.05.

Results: There were no signifcant differences in results of MMSE, BVRT (correct outcomes and errors) and CROFT
(second and point outcome) between total groups, but more missing data, lower total MMSE (p = 0.08) and CROFT
B-part seconds’ outcome (p = 0.06) in 11 pairs.
Conclusions:
1. Revealed differences are highly suspicious as artifacts because of low number of participants. 2. Possibility of prolonged
cognitive worsening in schizophrenia-hyponatraemia patients should be taken into account.
3. No influences of hyponatraemia on constructive praxis observed but disturbances in memory-controlling executive
systems probable.
4. Separate analysis for the role of polydipsia was not possible.
5. Overlap of the short- and long-term effects of hyponatraemia should be excluded.
6. For the future assesment of executive dysfunctions in schizophrenia-hyponatreamia patients, application of the battery
of higher-grade-of-sensitivity tests instead single measures is strongly recommended.