How does Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) differ from Multifocal Motor Neuropathy (MMN)?

Key Differences Between CIDP and MMN

CIDP and MMN are distinct immune-mediated demyelinating neuropathies with fundamental differences in their pathophysiology, clinical presentation, and treatment responses.

Pathophysiological Differences

• CIDP: Characterized by chronic inflammatory demyelination affecting both sensory and motor nerves 1
• MMN: Involves immune-mediated attack specifically on paranodal motor axons 1

Clinical Presentation

CIDP (Chronic Inflammatory Demyelinating Polyneuropathy)

• Pattern: Typically symmetrical involvement of nerves
• Distribution: Both proximal and distal muscle weakness
• Sensory symptoms: Present (numbness, tingling, sensory loss)
• Progression: Usually develops over weeks to months
• Reflexes: Often reduced or absent throughout

MMN (Multifocal Motor Neuropathy)

• Pattern: Asymmetric, multifocal involvement
• Distribution: Predominantly distal muscle weakness
• Sensory symptoms: Absent (purely motor)
• Progression: Often slower onset than CIDP
• Reflexes: May be preserved in some areas, absent in affected regions

Electrophysiological Findings

• CIDP: Shows diffuse demyelination with slowed conduction velocities, prolonged distal latencies, and conduction blocks in multiple nerves
• MMN: Features conduction blocks primarily in motor nerves with normal sensory conduction

Laboratory Findings

• CIDP: Often shows elevated cerebrospinal fluid protein without pleocytosis
• MMN: Frequently associated with anti-GM1 ganglioside antibodies (not seen in CIDP)

Imaging

• CIDP: MRI may show nerve hypertrophy in multiple nerves 2
• MMN: Nerve hypertrophy may be more focal and limited to motor nerves

Treatment Response

• CIDP: Responds to:

  • Corticosteroids
  • Intravenous immunoglobulin (IVIg)
  • Plasma exchange 3

• MMN:

  • Responds well to IVIg
  • May worsen with corticosteroids
  • Generally does not respond to plasma exchange 3, 4

Pathological Findings

Nerve biopsy can help differentiate these conditions:

• CIDP: Shows inflammatory demyelination with onion bulb formations
• MMN: Demonstrates chronic axonal neuropathy with less prominent demyelination 1

Diagnostic Approach

When evaluating a patient with suspected demyelinating neuropathy:

1. Assess for symmetry vs. asymmetry of symptoms
2. Determine if sensory symptoms are present
3. Perform nerve conduction studies looking for motor vs. sensorimotor involvement
4. Test for anti-GM1 antibodies if MMN is suspected
5. Consider nerve biopsy in difficult cases

Treatment Implications

The distinction between these conditions is critical for treatment decisions:

• Treating MMN with corticosteroids may worsen the condition
• IVIg is effective for both conditions but may be the only effective option for MMN
• Long-term maintenance therapy approaches differ

Variants to Consider

MADSAM (Multifocal Acquired Demyelinating Sensory and Motor Neuropathy, also known as Lewis-Sumner syndrome) represents an intermediate form with:

• Asymmetric presentation like MMN
• Both sensory and motor involvement like CIDP
• Treatment response more similar to CIDP 4, 2

Making the correct distinction between these conditions is essential for optimal treatment selection and patient outcomes.