Attenuated SEPs with no latency shifts in a family with hereditary spastic paraplegia

Five siblings with hereditary spastic paraplegia of autosomal-dominant inheritance were studied with somatosensory evoked potentials. Somatosensory evoked potentials were recorded from Cz', T12, and the left popliteal fossa following left posterior tibial nerve stimulation. The latency and amplitude of the corresponding potentials (i.e., P37, N20, and N7) were compared with normal values obtained from age- and height-matched controls. There was no significant difference in the values of N7, suggesting an intact afferent peripheral pathway; in contrast, the amplitudes of P37 and N20 were decreased with normal latencies. The degree of amplitude decrease correlated with the severity of vibration sense impairment in the lower limbs. These results appear to support selective axonopathy of the centrally directed axons of the dorsal root ganglion cells. Furthermore, our results suggest that different degrees of dorsal column involvement in hereditary spastic paraplegia can cause different types of somatosensory evoked potential abnormalities, namely, attenuated amplitudes with no latency shifts, as recorded in this family, and the prolonged latencies, as reported previously.