How do you differentiate between mononeuritis multiplex and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)?

Differentiating Mononeuritis Multiplex from CIDP

The key distinction is the pattern of nerve involvement: mononeuritis multiplex presents with asymmetric, multifocal involvement of individual peripheral nerves in a stepwise fashion, while CIDP typically manifests as symmetric, proximal and distal weakness with diffuse demyelination on nerve conduction studies. 1

Clinical Presentation Patterns

Mononeuritis Multiplex

• Presents with asymmetric sensory and/or motor deficits affecting multiple individual nerves in a non-contiguous distribution, with pain as a prominent feature, particularly when caused by inflammatory or vasculitic processes 1
• Develops in a stepwise pattern where individual nerves become involved sequentially over time, rather than simultaneously 2
• Can affect cranial nerves, causing focal deficits like facial weakness or visual disturbances 1
• The asymmetric presentation suggests different underlying pathology such as vasculitic neuropathy or inflammatory processes 1

CIDP (Typical Form)

• Characterized by symmetric proximal and distal muscle weakness with motor-dominant manifestation 3
• Progresses over more than 2 months, distinguishing it from acute conditions like Guillain-Barré syndrome 4
• Presents with diffuse, relatively uniform involvement rather than stepwise acquisition of deficits 1

Electrodiagnostic Findings

Mononeuritis Multiplex

• Nerve conduction studies show focal abnormalities in multiple individual nerves with asymmetric involvement 2
• Electromyography identifies discrete mononeuropathies affecting specific nerve distributions 2
• The pattern is multifocal rather than diffuse 1

CIDP

• Shows diffuse abnormalities with relatively uniform involvement of tested nerves 1
• Demonstrates evidence of demyelination including prolonged distal latencies, slowed conduction velocities, and conduction block 4
• The demyelination predominantly affects distal nerve terminals and nerve roots where the blood-nerve barrier is anatomically deficient 3

Cerebrospinal Fluid Analysis

• CIDP typically shows cytoalbuminologic dissociation (elevated protein with normal cell count), while this is not a characteristic feature of mononeuritis multiplex 4
• CSF analysis is recommended when inflammatory demyelinating polyradiculoneuropathy is suspected 2

Important Diagnostic Pitfall: MADSAM (Lewis-Sumner Syndrome)

A critical caveat is that Multifocal Acquired Demyelinating Sensory and Motor Neuropathy (MADSAM) represents an atypical CIDP variant that can mimic mononeuritis multiplex clinically. 4, 3

• MADSAM is characterized by asymmetric involvement with preserved reflexes in areas not affected by weakness 4
• It presents as chronic progressive demyelinating mononeuropathy multiplex that can evolve to a confluent pattern indistinguishable from typical CIDP 5
• MADSAM shows multifocal demyelination in nerve trunks, resulting in multiple mononeuropathy or asymmetric polyneuropathy 3
• Unlike true vasculitic mononeuritis multiplex, MADSAM responds to immunomodulatory therapy (though less favorably than typical CIDP) 5

Underlying Etiology Considerations

Mononeuritis Multiplex

• Common causes include vasculitis (particularly EGPA, polyarteritis nodosa), requiring ANCA testing and potentially deep skin biopsy 2
• Other causes include diabetes, sarcoidosis, and systemic inflammatory disorders 6, 2
• The presence of eosinophilia, asthma, or systemic vasculitis features suggests EGPA as the underlying cause 6

CIDP

• Represents an immune-mediated process with antibody-mediated demyelination in typical forms 3
• May be associated with diabetes, though this represents a diagnostic challenge as diabetics can develop both conditions 7

Treatment Response as a Diagnostic Clue

• Mononeuritis multiplex from vasculitis requires high-dose glucocorticoids combined with cyclophosphamide or other immunosuppressants 2
• CIDP responds well to IVIG, corticosteroids, or plasmapheresis as first-line therapy 4
• MADSAM responds to conventional immunomodulatory therapy but less favorably than typical CIDP 5
• Motor and sensory demyelinating mononeuropathy multiplex (MSDMM) shows good responsiveness to steroid treatment (80% of patients), unlike multifocal motor neuropathy 8

Diagnostic Algorithm

1. Assess the pattern of involvement: Asymmetric, stepwise acquisition of deficits suggests mononeuritis multiplex; symmetric, proximal and distal involvement suggests CIDP 1, 3

2. Perform nerve conduction studies: Focal, multifocal abnormalities point to mononeuritis multiplex; diffuse, uniform demyelination suggests CIDP 1, 4

3. Obtain CSF analysis: Cytoalbuminologic dissociation supports CIDP 4

4. Consider MADSAM if the clinical picture shows asymmetric involvement but electrodiagnostic studies demonstrate demyelination with conduction block in nerve trunks 4, 3

5. Evaluate for underlying vasculitis if mononeuritis multiplex is suspected: check ANCA, consider nerve or skin biopsy, assess for systemic features 2

6. MRI of brachial or lumbosacral plexus can help identify focal or diffuse peripheral nerve abnormalities and distinguish between the two conditions 4