Immunopathogenic biomarkers
| Immunopathogenic biomarker | When to test | Diagnostic utility | Utility in monitoring | Prognostic value |
| Autoantibodies | ||||
|
Anti-GM1 antibodies IgG IgM |
GBS with axonal neurophysiology Neuropathy with features of MMN | GBS + MMN +++ | 0 | GBS + MMN 0 |
|
Anti-GQ1b antibodies IgG | Patients with ataxia±ophthalmoplegia ± areflexia (MFS) or altered level of consciousness (BBE) | MFS ++++ GBS/MFS overlap ++ BBE ++ | ? | ? |
|
Anti-GD1a antibodies IgG | GBS with axonal neurophysiology | ++ | ? | ? |
|
Anti-GT1a antibodies IgG | GBS (PCB variant) | + | ? | ? |
| Anti-GD3/GD1b/GT1b - IgM | Ataxic neuropathies with IgM paraprotein | ++ | 0 | 0 |
| Paraproteins | 1) When a neuropathy is identified and a paraprotein is considered; 2) when a typical syndrome (eg, AL amyloidosis) is identified and neurological consequences are investigated; 3) in patients with a haematological process (eg, lymphoplasmacytic lymphoma) who develop symptoms of peripheral neuropathy. | Each paraprotein must be considered on its merits in terms of class, presumed antigen targeting activity, and specific underlying neuropathy. Many are coincidental and of no relevance to neuropathy or any neurological disease that coexists. | + (level of immunoglobulins and paraprotein decreases with successful anti-B-cell therapy) | 0 |
| IgM anti-MAG antibodies of strongly positive titre | Patients with suggestive phenotype, demyelinating neuropathy and IgM (usually kappa) paraprotein | +++ | 0 | 0 |
| Paranodal/nodal antibodies | Patients with inflammatory neuropathy poorly responsive to conventional therapies (steroids, IVIg, plasma exchange) plus additional features such as ataxia/tremor (NF155), or motor-predominant neuropathy and nephrotic syndrome (CNTN1), or neuropathic pain (CASPR1) | ++++ | ++ | ++ |
| Growth factors | ||||
| VEGF | 1) Patients with clinical features of POEMS syndrome, to confirm diagnosis. 2) Patients with acquired PN and slow motor CV, with lambda light chain gammopathy, particularly those with suspected CIDP. | ++++ | ++ | ++ (normalisation on treatment with no paraprotein implies ‘cure’) |
| NGF | Not clinically validated | 0 | 0 | 0 |
| BDNF | Not clinically validated | 0 | 0 | 0 |
Diagnostic utility, utility in monitoring and prognostic value are graded as 0, +, ++, +++, ++++, ? (unknown).
AL, amyloid light chain; BDNF, brain-derived neurotrophic factor; CIDP, chronic inflammatory demyelinating polyradiculoneuropathy; CV, conduction velocity; GBS, Guillain-Barré syndrome; MMN, multifocal motor neuropathy; NGF, nerve growth factor; PCB, pharyngeal-cervical-brachial variant of GBS; PN, peripheral neuropathy; POEMS, polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy—almost always lambda—and skin lesions.