Neuropsychological effects of konzo: a neuromotor disease associated with poorly processed cassava

Abstract

Background: Konzo is an irreversible upper-motor neuron disorder affecting children dependent on bitter cassava for food. Although the neuroepidemiology of konzo is well characterized, we report the first neuropsychological findings.

Method: Children with konzo in the Democratic Republic of Congo (mean age 8.7 years) were compared with children without konzo (mean age 9.1 years) on the Kaufman Assessment Battery for Children, second edition (KABC-II), and the Bruininks-Oseretsky Test of Motor Proficiency, second edition (BOT-2). Both groups were also compared with normative KABC measures from earlier studies in a nearby nonkonzo region.

Results: Using a Kruskal-Wallis test, children with konzo did worse on the KABC-II simultaneous processing (visual-spatial analysis) (K [1] = 8.78, P = .003) and mental processing index (MPI) (K [1] = 4.56, P = .03) than children without konzo. Both konzo and nonkonzo groups had poorer KABC sequential processing (memory) and MPI relative to the normative group from a nonkonzo region (K [2] = 75.55, P < .001). Children with konzo were lower on BOT-2 total (K [1] = 83.26, P < .001). KABC-II MPI and BOT-2 total were predictive of konzo status in a binary logistic regression model: odds ratio = 1.41, P < .013; 95% confidence interval 1.13-1.69.

Conclusions: Motor proficiency is dramatically affected, and both children with and without konzo have impaired neurocognition compared with control children from a nonoutbreak area. This may evidence a subclinical neurocognitive form of the disease, extending the human burden of konzo with dramatic public health implications.

FIGURE 1

Child and mother affected by konzo in the Democratic Republic of Congo. Photograph by Thorkild Tylleskar.

FIGURE 2

Box plots for the konzo groups (nonkonzo, konzo) and the Kikongo normative control group by gender for the KABC global scales (sequential processing, simultaneous processing, mental processing index) and memory subtests (hand movements, number recall, word order). Top and bottom of the box at the third and first quartiles, bisected by the median with outliers plotted as individual data points. American normative mean of 100 at dashed line (SD = 15) for standardized global scores, and a normative mean of 10 (SD = 3) for scaled subtest scores.

FIGURE 3

Schematic of the functioning and disability profile in konzo based on the International Classification of Functioning, Disability and Health, 2nd edition (ICIDH-2). This figure shows what a neuropsychological assessment can add to this disability-based classification scheme. It contributes by bridging the neurologic severity of the disease (either preclinical or full konzo) with the child’s functional status in the community. (Adapted from Tshala-Katumbay D, Eeg-Olofsson KE, Tylleskär T, Kazadi-Kayembe T. Impairments, disabilities and handicap pattern in konzo—a non-progressive spastic para/tetraparesis of acute onset. Disabil Rehabil. 2001;23(16):735, Figure 2).