To the Editor. —It was with great interest that we read the report by Younger et al about primary lateral sclerosis in the December 1988 issue of theArchives. 1 The report contains several interesting points; however, we would like to make some comments that might be of value during the diagnostic workup in this group of patients. The group of patients with primary lateral sclerosis described by Younger et al is heterogeneous, and includes cases with lung cancer, lower motor neuron affection, and human immunodeficiency virus seropositivity. We have recently described a patient presenting with slowly progressive gait disturbance evolving over 14 months and signs restricted to upper motor neurons ("corticospinal tract signs"). Results of myelography, computed tomographic scans of the brain and spine, electromyography, and evoked potentials were all normal, as were extensive microbiological testings, including syphilis serology. However, the cerebrospinal fluid contained high levels of antibodies against
