The cognitive profile of children treated with radiation for acute lymphoblastic leukaemia

S-J Whitaker, E Schutte
2012 South African Journal of Child Health  
ARTICLE S A J o u r n a l of C h i l d H e al th Demyelination induced by the radiation used in the treatment of childhood acute lymphoblastic leukaemia (ALL) diminishes the white matter in the brain. 1 At least one neuropsychological consequence of demyelination is a reduction in processing speed. 2 A brain region identified as being particularly sensitive to disruptions in white matter integrity is the prefrontal cortex, an area associated with functional working memory. 3 These changes may
more » ... versely impact on neuropsychological functioning. Structurally, the ratio of white to gray matter is significantly greater in the right than in the left cerebral hemisphere. 4 In terms of hemispheric specialisation, speech and language functions are in most cases lateralised to the left hemisphere and visuospatial functions to the right. 5 Given the uneven distribution of white matter in the brain and radiation-induced demyelination, we expected to see deficits in right hemisphere visuospatial memory tasks more than in left hemisphere verbal memory tasks. Previous research findings have shown that children with ALL show evidence of slight deficits in verbal tasks but that primary impairment is evident in visuospatial tasks. 6,7 Primary visuospatial impairment has also been reported in studies finding that ALL survivors showed reduced performance on visuospatial tests despite normal IQ scores. 8 These findings suggest abnormalities in the white matter tracts of the right hemisphere. Objectives The current study evaluated the cognitive test performance of a cohort of children treated with a standard dosage of 18 Gy of cranial radiation for ALL. The questions under investigation were whether the cohort of patients showed differences in performance between verbal and visuospatial tasks, whether there was reduced performance in tasks involving a speed component, and whether they showed evidence of deficits in working memory. Methods Sample The sample consisted of 8 patients who were attending a state hospital for the treatment of ALL at the time of the study. Informed consent was obtained from the guardians of the participants and minor assent was obtained from the participants. Participants were carefully selected on the basis of four inclusion criteria: (i) having received 18 Gy of cranial radiation, which is administered for central nervous system prophylaxis in phase 3 of the treatment regimen -10 fractions of the 18 Gy dose are administered over a period of 10 consecutive days; (ii) in the maintenance phase of treatment (phase 5) at the time of the study; (iii) age between 7 and 18 years; and (iv) in the formal schooling system, with a minimum of 5 years of formal education. The age range of the sample was 11 -17 years and there was an even male/female split. The sample was homogeneous with regard to treatment protocol, length of treatment, second-language Background. Cranial radiation is part of a treatment protocol for childhood acute lymphoblastic leukaemia (ALL) in South Africa. Radiation is known to disrupt the myelination and integrity of white matter tracts in the brain. Associated cognitive impairment has been well documented in other countries, but not to the same extent in the multicultural and multilingual South African context. Objectives. The current study focused on the assessment of memory and learning, two imperative cognitive functions. A quantitative evaluation of verbal and visuospatial memory performance in a cohort of ALL patients was done in order to establish whether there was a difference in performance between verbal and visuospatial tasks. Methods. Eight patients with a low socio-economic background and being educated in their second language were included in the cognitive evaluation. All had received 18 Gy of radiation as part of their treatment protocol and were on maintenance treatment at the time of the study. Results. In all the patients, primary cognitive impairment was demonstrated in ostensibly right hemisphere visuospatial tasks in comparison with ostensibly left hemisphere verbal tasks. Because deficits in visuospatial attention and working memory were identified, qualitative analysis of the results suggested that the white matter tracts in the right frontoparietal region and prefrontal cortex may be particularly vulnerable to radiation injury. Conclusion. The study findings support vulnerability of the right hemisphere, particularly the right frontoparietal region and prefrontal cortex, to radiation injury. The decline in visuospatial cognitive abilities has major implications for second-language learners, as visuospatial learning is particularly important for them.
doi:10.7196/sajch.475 fatcat:bvvcblq6ungadppwe4cbjtqo2i