| Diagnostic category | Negative laboratory tests |
| Infectious | Blood/serology: parainfluenza virus, adenovirus, rhinovirus, respiratory syncytial virus, HIV, flava cirus, west nile virus, herpes simplex virus, cytomegalovirus, lyme, California equine encephalitis (initially equivocal, then negative on subsequent testing)Cerebrospinal fluid: syphilis, St. Louis encephalopathy, powassan, arboviruses, enterovirus, Chlamydia, mycoplasma, influenza (A and B), varicella zoster virus |
| Autoimmune | ANA, ENA, ANCA, antithyroperoxidase |
| Paraneoplastic | Antivoltage-gated potassium channels, antivoltage-gated calcium channels, anti-NMDA (NR-1) |
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