Objective: Small-cell lung carcinoma (SCLC) and limbic encephalitis are recognized g-aminobutyric acid-B receptor (GABA B R) autoantibody accompaniments. We sought to determine in a diagnostic serology laboratory the frequency and accompaniments (neurologic, oncologic, and serologic) of GABA B R-immunoglobulin G (IgG). Methods:We tested stored serum and CSF specimens from 3 patient groups for GABA B R-IgG by indirect immunofluorescence on mouse brain tissue and transfected HEK293 cells. Group 1 included 3,989 patients tested for GABA B R-IgG in service evaluation for suspected autoimmune encephalopathy. Group 2 included 49 patients with an unclassified CNS synaptic IgG detected (antedating descriptions of GABA B R autoantibody). Group 3 included 384 patients in whom $1 SCLC-predictive autoantibodies had been detected.Results: GABA B R-specific IgG was detected in 17 patients (serum, 14; CSF, 11). N-type calcium channel antibody coexisted with GABA B R-IgG in all seropositive patients of groups 1 and 2. In group 1, 7 of 3,989 patients were positive (0.2%). All had limbic encephalitis; 5 had SCLC. Four patients received immunotherapy and improved neurologically. In group 2, 5 of 49 patients were positive (10%). Three had limbic encephalitis, 1 had rapidly progressive encephalomyelopathy, and 1 had cerebellar ataxia. Two patients had SCLC and 1 had multiple myeloma. In group 3, 5 of 384 patients were positive (1.3%); titers were low (detected only by transfected cell assay). The neurologic presentations were diverse and attributable to coexisting T-cell-mediated autoimmunity (indicated by CRMP-5 IgG [2], ANNA-1 [2], and ANNA-3 [2]), rather than to GABA B R-IgG.Conclusion: GABA B R autoantibody is a marker of an uncommon but treatable paraneoplastic neurologic disorder, usually occurring in the setting of limbic encephalitis and SCLC. Autoantibodies specific for the CNS inhibitory g-aminobutyric acid-B receptor (GABA B R, B1 and B2 subunits) have been reported in patients with paraneoplastic limbic encephalitis (LE). Small-cell lung carcinoma (SCLC) and other neuroendocrine neoplasms 1,2 have been reported as oncologic accompaniments. The neuronal N-type voltage-gated calcium channel antibody, another paraneoplastic autoantibody SCLC marker, is commonly reported as a serologic accompaniment.1 Paraneoplastic neurologic disorders associated with autoantibodies targeting neural plasma membrane antigens (e.g., GABA B R) tend to improve with early cancer treatment and immunotherapy.1 In contrast, disorders associated with autoantibodies specific for neural intracellular antigens (i.e., nuclear and cytoplasmic) are less responsive to these treatments.To date, most patients reported with GABA B R antibody have been ascertained through evaluation of patients with LE.1,2 Autoimmune serologic evaluation in a clinical service laboratory, involving patients with diverse neurologic presentations, allows broader ascertainment of clinical associations. Here, we report the detection frequency of GABA B R antibody and associ...

Background: The expertise required for proper electroencephalography (EEG) setup can make the 10-20 array unwieldy in the hospital setting. There may be a role for an EEG array with reduced leads to improve the efficiency of inpatient practice. Methods: Clips from 100 EEG records, 50 ictal and 50 non-ictal, in adult inpatients from January 1, 2007, to January 1, 2012, were retrospectively reviewed and selected for digital lead reduction and blind review. Two epileptologists reviewed these tracings and documented the presence of seizures and severe disturbance of background. The reduced array included 7 leads spanning the scalp. Three different montages were available. Sensitivity and specificity of the reduced array were calculated using the formal EEG report as the comparison standard. Results: For the detection of any seizure, the reduced array EEG had a sensitivity of 70% and specificity of 96%. Sensitivity for identifying encephalopathic patterns was 62% and specificity was 86%. Focal seizures were more readily identified by the reduced array (20 of 25) than were generalized ictal patterns (13 of 25). Conclusion: The reduced electrode array was insufficiently sensitive to seizure detection. Reducing EEG leads might not be a preferred means of optimizing hospital EEG efficiency.