[Superficial siderosis of the central nervous system: an electrophysiological study]

Superficial siderosis of the central nervous system (SS) is a rare neurological disorder characterized by symptoms such as neurosensory hearing loss, ataxic gait, and spastic paraparesis. Recently, magnetic resonance imaging (MRI) enables us to make a clinical diagnosis. However, the exact pathophysiological mechanism underlying this disorder remains uncertain. Although iron chelation therapy has been attempted experimentally, it has not been successful and there is no effective medical treatment available. Towards the better understanding of the pathophysiological mechanism underlying SS, we performed electrophysiological studies, in which multiple evoked potential studies were included, in 3 patients with SS. Somatosensory evoked potentials (SEPs) evoked by median nerve stimulation were all normal, but those evoked by the posterior tibial nerve stimulation showed a significant delay of the latency of P40. In the auditory brainstem response (ABR) studies, there were no reproducible responses of the brainstem origin. In the blink reflex studies, R2 latency was delayed in one patient. In visual evoked potential (VEP) studies, the latency of P100 was delayed in two of three patients, unless all the patients clinically showed no visual symptom. The nerve conduction velocity studies performed in peripheral nerves of upper and lower extremities were all normal. The abnormal findings of ABR and SEP may suggest that the acoustic nerve and the posterior funiculus of the spinal cord are involved, respectively. These findings are also in a good agreement with pathological findings of SS reported in the literature. In SS, the hemosiderine accumulation is usually less severe in the visual tract; however, the delay of VEPs may suggest the latent dysfunctioning of the visual system in SS. It is suggested that multiple evoked potential study is useful for clinical evaluation of SS.