In an adult with suspected chronic inflammatory demyelinating polyneuropathy, which antibodies should be tested?

Antibody Testing in Suspected Chronic Inflammatory Demyelinating Polyneuropathy

In adults with suspected CIDP, you should test for antibodies against nodal-paranodal proteins (neurofascin-155, neurofascin-186, contactin-1, and Caspr1), anti-ganglioside antibodies (particularly anti-GM1 IgG and anti-LM1 IgG), and screen for monoclonal gammopathies with serum protein immunofixation electrophoresis.

Core Antibody Panel

The antibody workup should be structured in tiers based on diagnostic yield and clinical implications:

First-Tier Essential Testing

• Nodal-paranodal antibodies (IgG4 subtype):
  • Anti-neurofascin-155 (NF155) - found in ~10% of CIDP patients 1
  • Anti-contactin-1 (CNTN1) - found in ~4-6% 1, 2
  • Anti-Caspr1 - found in ~6% 1
  • Anti-neurofascin-186/140 (NF186/140) - found in ~4% 1

These antibodies define "autoimmune nodopathy," a distinct entity with critical treatment implications. Patients with these antibodies typically show poor response to IVIG (only 14% effective) but excellent response to rituximab (75% effective) 1, 3. This fundamentally changes management, making their detection essential before initiating therapy 4.

Second-Tier Testing

• Anti-ganglioside antibodies:

  • Anti-GM1 IgG (associated with multifocal motor neuropathy overlap)
  • Anti-LM1 IgG (associated with CIDP) 5
  • Anti-disialosyl ganglioside IgM (for chronic ataxic neuropathy phenotype) 5

• Serum protein immunofixation electrophoresis (not just SPEP):

  • Detects monoclonal gammopathies in ~10% of polyneuropathy patients 6
  • IFE is superior to SPEP, detecting 30% of IgM gammopathies missed by SPEP alone 6
  • Anti-MAG IgM antibodies should be tested if IgM paraprotein detected 5, 4

Clinical Context for Testing

When Nodal-Paranodal Antibodies Are Most Likely

Test with high suspicion when patients present with:

• Younger age at onset (anti-NF155 patients average 19.6 years vs. 55 years for anti-Caspr1) 1
• Severe motor impairment requiring walking assistance
• Cranial nerve involvement (present in ~45% of antibody-positive cases) 1
• Autonomic disturbances 1
• Poor or absent response to IVIG - this is the key red flag 7, 8
• Markedly prolonged distal motor latencies, especially in ulnar and tibial nerves 1

Distinguishing Features by Antibody Type

Anti-NF155 patients show more severe nerve damage electrophysiologically with longer distal motor latencies compared to anti-Caspr1 patients 1. Both groups have high rates of non-recordable sensory responses (67% of sensory nerves) and motor responses (14% of motor nerves) 1.

Additional Metabolic Screening

While not antibody testing per se, concurrent screening helps exclude mimics:

• Vitamin B12 with metabolites (methylmalonic acid ± homocysteine):

  • B12 deficiency found in 2-8% of polyneuropathy patients 6
  • Metabolites detect 44% of B12-deficient cases missed by B12 level alone 6
  • Methylmalonic acid is more specific than homocysteine 6

• Glucose tolerance testing:

  • Pre-diabetes found in 25-36% of idiopathic polyneuropathy 6
  • Consider when fasting glucose is borderline

Testing Methodology

Use cell-based assays (CBA) for nodal-paranodal antibodies - this is the gold standard method that allows IgG subtype identification 1. The IgG4 subtype is pathogenic and clinically relevant 7, 8.

Common Pitfalls to Avoid

1. Don't rely on SPEP alone - use immunofixation electrophoresis to avoid missing small monoclonal proteins 6

2. Don't assume IVIG failure means non-CIDP - it may indicate antibody-mediated nodopathy requiring rituximab instead 3, 4

3. Don't test only anti-ganglioside antibodies - the nodal-paranodal antibodies have higher clinical impact on treatment decisions 4

4. Don't skip antibody testing in atypical presentations - variants like distal-predominant or pure motor/sensory forms may still be antibody-mediated 9

The 2021 EAN/PNS guidelines now recognize autoimmune nodopathy as a separate diagnostic category from classic CIDP, emphasizing that antibody detection is not just academic but changes fundamental treatment approach 3. Testing for these antibodies before initiating therapy allows you to avoid ineffective IVIG treatment and proceed directly to rituximab in antibody-positive cases 3, 4.