Muscle antibodies in the cerebrospinal fluid from patients with myasthenia gravis.

IgG antibodies to nicotinic acetylcholine receptor (AChR) and to a muscle antigen extracted by citric acid, were quantified in serum and cerebrospinal fluid (CSF) from 28 patients with myasthenia gravis, and the serum:CSF ratios compared with those of total IgG. Agarose-electrophoresis and calculations of the IgG index and Tourtellotte's formula were performed. No evidence of intrathecal antibody synthesis was demonstrated. Compared to the total IgG concentrations in serum and CSF, the CSF concentrations of IgG AChR antibodies were lower than expected.