POST-RADIATION NEUROCOGNITIVE DEFICIT IN THE CHORNOBYL CLEAN-UP WORKERS: GERIATRIC ASPECTS (PART І).

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 controlgroups. The randomized sample of the male elderly participants (attained age more than 60 years old) in liquidationof 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 StateInstitution «National Research Center for Radiation Medicine, Hematology and Oncology of The National Academyof 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 PsychoneurologyDepartment 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 furtherexpert 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 werefound (p < 0.01) with a tendency to the current performance intelligence coefficient (pIQ) decrease in the subjectsof the main group (p = 0.08). In the main group of clean-up workers, significantly higher levels of full IQ deficit werefound 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 ofthe WAIS scale was observed in the elderly Chornobyl clean-up workers. With higher radiation doses (> 50 mSv), theseverity of cognitive deficit increases. In the clean-up workers irradiated at doses > 50 mSv when compared to thenon-exposed comparison group, significantly lower values of actual full and verbal IQs were found (p < 0.05) withsignificantly higher values of intellectual disharmony (p < 0.05). When exposed to doses of more than 0.3 Sv, in theChornobyl clean-up workers above 60 years old, a characteristic dose-dependent psychometric pattern was firstrevealed, 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 ofthe Chornobyl disaster, is of extremely great medical and social significance and can prevent the disability andsocial maladaptation in this cohort. Modern cheap and non-invasive psychophysiological and neuropsychiatricmethods of diagnosing neurocognitive dysfunctions can be successfully used both in scientific research and ineveryday 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 changesand ionizing radiation on cognitive functioning.