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Evoked potential abnormalities in progressive spastic paraparesis associated to HTLV‐1

The electrophysiological features of progressive spastic paraparesis (PSP) associated with HTLV‐1 in Chile, a non‐tropical country, are presented. Twenty‐two of 45 PSP subjects were positive for HTLV‐1 antibodies. Trimodal evoked potentials were all normal in only 2 of these cases (9.1%). Somatosensory evoked potentials (SSEPs) were abnormal in 19 patients (86.3%) with a mean amplitude of 1.31 uV SD 0.92. Visual evoked potentials (VEPs) and brainstem auditory evoked potentials (BAEPs) were normal in all patients except four. Peripheral nerve conduction was normal in all but one who showed discrete slowness of the motor conduction velocity in the peroneal nerves. EMG was normal in 15 cases in whom it was performed. SSEP's were abnormal in 2 (8.7%) of 23 HTLV‐1 negative cases with a mean amplitude of 2.4 uV SD 1.5, which is statistically different with respect to the positive cases (p < 0.001). These results support an involvement of the spinal cord not restricted to the pyramidal tracts but also including subclinical damage of the posterior columns in PSP associated to HTLV‐1.