Visual Evoked Potentials in Konzo, a Spastic Paraparesis of Acute Onset in Africa

Aim: To assess whether or not visual evoked potentials (VEPs) are abnormal in konzo, a para/tetraparesis of sudden onset, and to correlate the findings to the clinical picture of the disorder. Methods: VEPs were recorded in 23 patients (9 men and 14 women, mean age: 23 ± 10 years) suffering from konzo, and 38 healthy subjects (20 men and 18 women, mean age: 27 ± 15 years). The mean P100 latencies and peak-to-peak N75-P100 amplitudes of each eye were measured and compared in the two groups. The mean interocular P100 latency and amplitude differences were calculated and also compared. Results: VEPs were abnormal in 11/23 patients (48%) consisting of P100 prolongation (7 subjects), absence of P100 wave (2 subjects) or an atypical waveform (2 subjects). The mean P100 latency value of the konzo group was significantly increased as compared with the mean (+ 2.5 SD) of the reference values from healthy subjects (p < 0.05). There was a statistically significant decrease of amplitude in konzo patients compared to normal subjects (p < 0.05) with, however, only 2 patients outside the 95% confidence limits. Six patients (27%) had abnormal VEPs despite normal visual acuity. These abnormalities were symmetric and a relation could be found between neither the duration nor the severity of the disease and the VEP perturbation. Conclusion: The main features of these abnormalities are delayed P100 latency and decreased amplitude. These findings indicate involvement of visual pathways and seem to suggest the presence of axonal loss in the prechiasmal visual pathways in konzo. This study provides evidence that the neurodamage in konzo extends to the visual pathways.