🧠Autoimmune paranodopathies

Autoimmune Paranodopathies (Paranodal Neuropathies)

Definition:
Immune-mediated neuropathies targeting paranodal axo–glial junctions, distinct from CIDP, with different pathophysiology, clinical features, and treatment response.

🔹 1️⃣ Pathophysiology

• 🧬 Target proteins at paranode:
  • NF155 (glial)
  • NF186 / NF140 (axonal)
  • Contactin-1 (CNTN1)
  • CASPR1
• ⚡ IgG4 antibodies:
  • Minimal complement activation
  • No macrophage-mediated demyelination
• 🧠 Effect: Node/paranode detaches → conduction failure without classic demyelination

🔹 2️⃣ Clinical Features

• Severe sensory ataxia (out of proportion to weakness)
• Prominent postural & kinetic tremor
• Early gait imbalance
• Subacute distal weakness or sensory loss
• Red flags for paranodopathy:
  • Poor/no IVIG response
  • Rapid progression
  • Very high CSF protein
  • Conduction block with minimal temporal dispersion
  • Severe early symptoms

🔹 3️⃣ Antibody-Specific Phenotypes

🔹 4️⃣ Electrophysiology

• Conduction block with minimal temporal dispersion
• Prolonged distal motor latencies
• Reduced CMAP amplitudes
• Myelin morphology preserved early
• ✅ Key distinction from classic CIDP

🔹 5️⃣ Diagnosis

• 🧪 Serum antibodies: NF155, NF186, CNTN1, CASPR1
• 💉 CSF: markedly elevated protein
• 🩻 MRI: possible nerve root thickening
• ⚕️ Kidney workup if CNTN1 positive

🔹 6️⃣ Treatment

Ineffective:

• ❌ IVIG (except NF186+)

Effective:

• 💉 Rituximab → first-line for IgG4 paranodopathies
• ⚗️ Plasma exchange (PLEX) → rapid improvement
• 🌡 Steroids: variable

Long-term:

• RTX every 6–12 months
• Consider azathioprine / mycophenolate as adjuncts

🔹 7️⃣ Prognosis

• ✅ Good if treated early before secondary axonal loss
• ❌ Poor if delayed diagnosis / IVIG-resistant
• Rituximab dramatically improves long-term outcomes

💡 High-Yield Clinical Pearl

• Severe sensory ataxia + tremor + conduction block with minimal temporal dispersion + NO IVIG response → excellent response to Rituximab