POST-RADIATION NEUROCOGNITIVE DEFICIT IN THE CHORNOBYL CLEAN0-UP WORKERS: GERIATRIC ASPECTS (PART І)
Authors:   State Institution «National Research Center for Radiation Medicine, Hematology and Oncology of the National Academy of Medical Sciences of Ukraine», Kuts K. V. , Loganovsky K. M. ,   State Institution «National Research Center for Radiation Medicine, Hematology and Oncology of the National Academy of Medical Sciences of Ukraine»
Published: December 2024

Objective: to study the features of cognitive disorders in the remote period following exposure to ionizing radiation (IR) in the elderly participants of the liquidation of the consequences of the Chornobyl NPP accident (Chornobyl clean-up workers) with chronic cerebrovascular disorders.
Materials and methods. The retrospective and prospective cohort study with the external and internal control groups. The randomized sample of the male elderly participants (attained age more than 60 years old) in liquidation of the consequences of the accident (Chornobyl clean-up workers, liquidators) at the Chornobyl nuclear power plant (ChNPP) in 1986–1987 (main group, n = 52) recruited from the Clinico-epidemiological registry (CER) of State Institution «National Research Center for Radiation Medicine, Hematology and Oncology of The National Academy of Medical Sciences of Ukraine» (NRCRMHO) with verified chronic cerebrovascular disorders (CVD) was examined. The comparison group (n = 13) consisted of the unexposed in- and out-patients of the Radiation Psychoneurology Department of Institute for Clinical Radiology (ICR) of NRCRMHO with the corresponding age and sex (the comparison group). The internal control group included the liquidators irradiated at doses < 50.0 mSv (n = 12). The psychometric methods (Wechsler Adult Intelligence Scale (WAIS) with premorbid IQ (pre-IQ) assessment and further expert estimation of neurocognitive status) applied. The methods of descriptive and variation statistics, parametric and non-parametric criteria, regression-correlation analysis were used.
Results. In the main group of the Chornobyl clean-up workers, when compared with the non-exposed control group, significantly lower actual (obtained during direct testing) full (fIQ) and verbal (vIQ) intelligence coefficients were found (p < 0.01) with a tendency to the current performance intelligence coefficient (pIQ) decrease in the subjects of the main group (p = 0.08). In the main group of clean-up workers, significantly higher levels of full IQ deficit were found compared to premorbid levels (p < 0.01), mainly due to a significantly higher level of verbal IQ deficit (p < 0.001). A dose-dependent decrease in indicators of both verbal and performance (non-verbal) psychometric tests of the WAIS scale was observed in the elderly Chornobyl clean-up workers. With higher radiation doses (≥ 50 mSv), the severity of cognitive deficit increases. In the clean-up workers irradiated at doses ≥ 50 mSv when compared to the non-exposed comparison group, significantly lower values of actual full and verbal IQs were found (p < 0.05) with significantly higher values of intellectual disharmony (p < 0.05). When exposed to doses of more than 0.3 Sv, in the Chornobyl clean-up workers above 60 years old, a characteristic dose-dependent psychometric pattern was first revealed, which consists of a significant decrease in actual performance IQ (r = -0.46; p = 0.039) with a simultaneous increase in performance IQ deficit in comparison with the premorbid levels (r = 0.55; p = 0.011).
Conclusions. Timely detection and monitoring of neurocognitive disorders in the elderly, specifically in victims of the Chornobyl disaster, is of extremely great medical and social significance and can prevent the disability and social maladaptation in this cohort. Modern cheap and non-invasive psychophysiological and neuropsychiatric methods of diagnosing neurocognitive dysfunctions can be successfully used both in scientific research and in everyday clinical practice of neurologists, psychiatrists, neuropsychologists, and clinical neurophysiologists. Postradiation neurocognitive deficit has its specific features consisting of diffuse organic damage to both left (dominant) and right (subdominant) brain hemispheres, which can testify to the synergistic effect of age-related changes and ionizing radiation on cognitive functioning.
Key words: Chornobyl disaster, ionizing radiation; elderly age; cognitive disorders; Wechsler Adult Intelligence Scale.