SOMATOSENSORY EVOKED POTENTIAL IN GLUCOSE TRANSPORTER 1 DEFICIENCY SYNDROME (GLUT1-DS) BEFORE AND DURING KETOGENIC DIET

Objectives: Glucose transporter 1 deficiency syndrome (Glut1-DS) is a rare syndrome with intractable epilepsy, ataxia, dystonia, hypotonia, mental retardation and spasticity. Ketogenic diet (KD) is reported to improve clinical symptoms and EEG findings in Glut1-DS. We investigated somatosensory evoked potential (SEP) to evaluate its usefulness in the diagnosis of Glut1-DS and the effects of KD.

Methods: Five cases (3y-8y, mean 6y) of Glut1-DS were investigated. All had above mentioned typical symptoms from infancy or early childhood and were diagnosed as Glut1-DS because they had hypoglycoracchia (CSF glucose <40mg/dl, CSF/blood glucose ratio <0.4) and decreased uptake of radioisotope labeled glucose into erythrocytes in vitro. After KD was started, all cases showed clinical and EEG improvement. SEP was examined in all cases before KD and during KD in 4 cases using NEC San-ei Synax 1100 (Japan) under sedation. Median nerve was stimulated electrically 500 to 1000 times at 3.5Hz. Cortical response was recorded from C3' or C4' (Fz reference) and results were confirmed by double tracing. Peak amplitude and time latency of early cortical response (N20) was investigated.

Results: Before KD, all cases showed abnormal N20: absent in 2 cases and markedly decreased amplitude in other 3 case, but peak latency was not delayed. During KD, N20 became to be detected in 2 cases in whom it was absent before KD, and increased in amplitude in other 2 cases in whom it was markedly decreased before KD. One case became difficult to continue KD strictly and showed clinical worsening with more decreased amplitude of N20 compared to previous SEP on strict KD.

Conclusion: This is the first report on SEP in Glut1-DS. N20 was absent or markedly decreased in Glut1-DS. Its amplitude increased during KD. SEP is also considered to be useful as a good marker to evaluate the effects of KD.