How do you approach a mildly positive finding on an autoimmune encephalitis panel when there is no other evidence of encephalitis (such as elevated CSF protein, abnormal imaging, or EEG findings)?

In general, low positive Abs by ELISA or radioimmunoprecipitation assays have low predictive value for neurological disease and cancer outside of specific clinical contexts (e.g. a PQ of 0.03 nmol/L in a patient with myasthenic syndrome).

For encephalitis, GAD65 < 20 nmol/L, and PQ type calcium channel Ab < 1.00 nmol/L, these can be informative, but probably no more so than a positive antinuclear Ab (ANA). They are considered to have low positive predictive value for autoimmune encephalitis, and other parameters should be considered (acuity of onset, findings in MRI, EEG, and CSF testing). For low GAD65 Ab, I recommend to check B12, thyroid function, and HBA1C/fasting glucose to ensure more common non neurological autoimmune disease associat...

Antibody levels can fluctuate; therefore, I don’t think there’s one good answer. If one goes with clinical symptomatology and follows the patient clinically, it might be too late because the fundamental premise is to get treatment initiated early. So I tend to RX antibody negative cases because the clinical picture dominates everything else. Besides, there is no requirement that an antibody needs to be positive for treatment initiation either in the acute or chronic phase of the disease. In the acute phase, treatment needs to commence anyway since antibodies take anywhere from 2 to 3 weeks to return.