To the Editor.
—Caroscio and others1 have examined CSF from an extensive series of patients with multiple sclerosis (MS) and other diseases. The results of their quantitative CSF IgG measurements largely support our findings2 and those of others. We would like to respond to their implied criticism of our low rate (3.5%) of false-positive IgG index results among 160 patients with other neurologic diseases. Contrary to their speculation, this result was not obtained through lack of "blinding." The technicians performing the assays were unaware of the patients' clinical diagnoses. The investigator reviewing the charts was usually unaware of the IgG data. In calculating this figure, we eliminated the data from patients with CNS infections or immunologic disorders (40% of those patients had elevated CSF IgG indexes). Summing the data from these "control" groups, our false-positive rate averaged 11%, which is the same as that reported by Link and
Hershey LA, Scillian JJ, Trotter JL. Quantitative CSF IgG Measurements. Arch Neurol. 1984;41(5):473. doi:10.1001/archneur.1984.04050170015003
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