| Autoantibody testing in Neuropathy |
 | Initial evaluation of Neuropathy: history, examination and electrodiagnostic
studies to define the neuropathy
 | symmetric vs. asymmetric |
| sensory vs. motor |
| axonal or demyelinating and if
conduction block is present |
| If the etiology for the PN is not apparent, check a serum SPEP and IFE
for monoclonal protein |
| Urine testing for a paraprotein is done in some cases, particularly
patients with primarily small-fiber sensory or autonomic involvement.
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| Sensory or sensorimotor PN |
| Demyelinating neuropathy with IgM gammopathy: particularly if there
is prolonged distal latencies, anti-MAG testing is performed.
| Early in the course, these patients have sensory greater than motor
deficits that are primarily distal. |
| Most patients with positive anti-MAG will have an IgM monoclonal protein. |
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| Pure sensory syndromes (Ganglionopathy):
| Especially if asymmetric, rapidly progressive, sensory loss involving
proprioception. |
| Anti-Hu testing is performed, commonly associated with small cell
neoplasms, especially from the lung. |
| A positive anti-Hu antibody result may herald an underlying
malingnancy. |
|
| GALOP Syndrome:
anti-CMA antibodies
| Gait disorder; Autoantibody; Late-age Onset
Polyneuropathy |
| Appears to be immune-mediated |
|
| Sjogren syndrome
| with purely sensory neuropathies and gait
ataxia who have markedly elevated ANA titers but few other
laboratory abnormalities. |
| Lip biopsy, showing the typical inflammation
of minor salivary glands, can be a useful confirmatory test. |
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| Motor neuropathies |
| Adult onset, symmetric neuropathy, sensory involvement more profound than
motor.
| Especially in:
 | Patients over 50 years old |
| NCV showed demyelinating neuropathy with increased distal
latency. |
|
| Order anti-GM1 antibodies |
| Serum IgM M-protein postive in 85% |
| Also in neuropathy that cannot be easily distinguished from ALS. |
| Further
reading - Wash Univ |
|
| GBS patients when electrophysiologic studies suggest significant axonal
loss.
| Order anti-GM1 antibodies |
| Several studies have demonstrated that this antibody predict a more
severe GBS with worse recovery . |
|
| Suspected Miller Fisher syndrome or other forms of acute ophthalmoplegia
believed to be neuropathic in origin:
| Order anti-GQ1b antibodies |
| High sensitivity for these disorders. |
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| Interpretation of positive autoantibody results |
| Positive anti-MAG assay confirmed by Western blot
| Strongly suggestive of an immune-mediated PN, usually associated with an
IgM paraprotein. Some patients will fulfill diagnostic criteria for CIDP and should be
treated appropriately. |
|
| High-titer anti-GM1 IgM antibodies:
| highly specific for motor-predominant neuropathies, particularly those
believed to be immune-mediated, such as Multifocal motor neuropathy.
|
| Both IgM and IgG anti-GM1 antibodies have been observed in classic and
variant forms of GBS. |
| The specificity of low titers of anti-GM1 Ab is limited. |
|
| Anti-GQ1b antibodies
| Highly sensitive and specific for Miller Fisher syndrome. The presence of
this antibody excludes other conditions that cause ophthalmoplegia. |
|
| Positive anti-Hu assays:
| Suggest a paraneoplastic sensory neuropathy or neuronopathy and prompt a
search for an underlying malignancy. |
| Limbic encephalitis, cerebellar disorders can
also occur in association with this antibody. |
| A negative serology would indicate an alternate cause for the neuropathy. |
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| Further reading:
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