Characteristic response to transcranial magnetic stimulation in Rett syndrome

To pathophysiologically evaluate the corticospinal tracts (CSTs) in Rett syndrome (RS), transcranial magnetic stimulation (TMS) was performed in 3 patients aged 4, 6 and 13 years. The two younger cases exhibited the clinical characteristics of the pseudostationary stage (stage III), while ambulation was lost in the oldest case at the age of 11 years (stage IV). The motor cortex and cervical spinal roots were magnetically stimulated to obtain motor evoked potentials (MEPs) from the relaxed first dorsal interosseous muscle. Compared with the central motor conduction time (CMCT) in age-matched normal children, CMCT in the stage III cases was significantly short (6.9-7.1 ms, P < 0.05). In the stage IV case, CMCT was markedly short but not significantly so (6.6 ms, P = 0.06), which was partly due to a significant increase in the threshold intensity of TMS (100%, P < 0.05). Thus, the CMCT shortening, which implied unique cortical hyperexcitability, was considered consistent and characteristic of RS. The CSTs in the stage IV case were certainly impaired, corresponding well to the progressive spastic paresis.