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To the Editor.
—In Russo's recent article in the Archives (1982;39:662-664), he reported four cases of idiopathic late-onset spastic paraparesis and argued for the existence of "primary lateral sclerosis" as a disease entity.I am concerned that he did not mention visual or brain-stem evoked potentials. My colleagues and I recently studied 40 patients (24 male, 16 female; mean age, 56 years) with progressive spastic paraparesis of late onset, who had no family history of neurologic disorder and no clinical or historical evidence of scattered nervous system lesions. Thirty-three percent had abnormal visual evoked responses, indicating second lesions, and an additional 15% had abnormal brain-stem auditory evoked responses, indicating an extraspinal, if not necessarily second, lesions. Of the 67% of patients with sensory bladder disturbance, 44% had abnormal evoked potentials, and of the 33% with a pure motor disorder, 46% had abnormal evoked potentials.We found a very low incidence