Autoimmune Neurology

The differences in the major Quest antineural antibody panels are related to reflex patterns and the specimen types tested. The key component of these panels is screening by tissue immunofluorescence (TIF). The other 2 components are testing for autoantibodies against (1) intracellular and nuclear antigens using line blot (LB) and/or (2) cell surface antigens using transfected cell-based assay (CBA). Serum or cerebrospinal fluid (CSF) is tested for evidence of antibodies using rat hippocampus, monkey cerebellum, and monkey sural nerve.

In the basic paraneoplastic panels (test code 93876 for serum; test code 94536 for CSF; see Table), specimens with suspicious results by TIF reflex to specific testing for autoantibodies against intracellular and nuclear antigens using LB and/or autoantibodies against cell surface antigens using transfected CBA. However, if no suspicious fluorescence is seen, no additional testing is performed.

TIF is primarily useful for antibodies against intracellular and nuclear antigens, not cell surface antigens. Therefore, we also offer expanded paraneoplastic panels (test code 94957 for serum; test code 94960 for CSF; see Table), in which CBA for cell surface autoantibodies is performed whether TIF is positive or not. Separate panels identical to these expanded paraneoplastic panels are also available for patients presenting with suspected autoimmune encephalitis (test code 94958 for serum; test code 94955 for CSF; see Table) or epilepsy (test code 94956 for serum; test code 94959 for CSF; see Table). Note that no additional testing for antibodies against intracellular or nuclear antigens is performed unless fluorescence patterns suspicious for these antibodies are seen.

If providers want specific immunoassay testing by both LB and CBA regardless of the TIF screening result, a comprehensive serum panel (test code 93888; see Table) is available in which both LB and CBA are performed whether TIF is positive or not.

All of the serum panels also include immunoassay testing for antibodies against several neuromuscular junction antigens because these antibodies cannot be detected by indirect immunofluorescence with the tissue substrates we use.

Most autoantibodies associated with autoimmune neurological disorders are detected in both serum and cerebrospinal fluid (CSF), but there are exceptions. In one large study, both types of specimens yielded positive results in 88% of patients but only one or the other was positive in 12%.¹

Some autoantibodies are better detected in one specimen type or the other.² Antibodies related to voltage-gated potassium channels (CASPR2 and LGI1) and antibodies associated with neuromyelitis optica spectrum disorders (aquaporin 4 and myelin oligodendrocyte glycoprotein) may only be detected in serum. Similarly, antibodies against neuromuscular junction antigens associated with myasthenia gravis are more likely to be detected in serum. Antibodies against N-methyl-D-aspartate receptor (NMDAR) are more likely to be detected in CSF.

When possible, paired serum and CSF specimens should be tested.