Primary Lateral Sclerosis-Reply

In Reply.  —Dr Gibson's letter was read with interest. My colleagues and I agree fully with his conclusion regarding the need for evoked response studies in the evaluation of progressive spastic paraparesis. Reports on familial spastic paraplegia¹³ have shown abnormal visual evoked responses in some cases. When our initial report was submitted, we were not equipped to carry out these tests. We subsequently did perform patternshift studies of visual and brain-stem auditory evoked potentials in our four patients and found no abnormalities. We therefore conclude, on clinical and electrophysiologic grounds, that our four patients do represent a nosologie entity, ie, primary lateral sclerosis. Finally, we find the data from Dr Gibson's series of 40 patients most interesting. Though 48% did have abnormal evoked responses, 52% did not. This group of 21 patients, assuming they fulfill other clinical criteria, provides strong evidence for the existence of primary lateral sclerosis as a separate