Is asymmetric/multifocal neuropathy characterized by asymmetric, multifocal distribution of weakness and/or sensory loss in polyneuropathy?

Asymmetric/Multifocal Neuropathies in Polyneuropathy

Yes, the description of asymmetric/multifocal neuropathies as having asymmetrical, multifocal distribution of weakness and/or sensory loss in polyneuropathy is correct. 1

Clinical Characteristics of Asymmetric/Multifocal Neuropathies

• Asymmetric/multifocal neuropathies present with asymmetric sensory and/or motor deficits affecting multiple individual nerves or nerve roots, with pain as a prominent feature, particularly in inflammatory or vasculitic causes 1, 2
• Symptoms often begin in one limb or nerve territory and progress to involve other areas in a patchy, non-length-dependent manner, contrasting with the classic distal symmetric pattern seen in most polyneuropathies 1
• The degree of motor and sensory loss varies based on the underlying cause, with different presentations in specific conditions 1, 2

Specific Types of Asymmetric/Multifocal Neuropathies

Multifocal Motor Neuropathy (MMN)

• Characterized by chronic progressive, asymmetric distal limb weakness, predominantly affecting the upper extremities 3, 4
• Presents with slowly progressive, asymmetric distal limb weakness without sensory loss 3
• Electrodiagnostic studies reveal motor conduction blocks at non-compressible sites 4
• Anti-GM1 antibodies are elevated in less than half of patients 4

Lewis-Sumner Syndrome (MADSAM)

• Presents with asymmetric, multifocal sensory and motor deficits 5, 6
• Can be misdiagnosed as compressive neuropathies like carpal tunnel syndrome 6
• Considered a variant of chronic inflammatory demyelinating polyneuropathy with asymmetric presentation 5

Vasculitic Neuropathy (Mononeuritis Multiplex)

• Presents with acute/subacute onset of asymmetric, painful sensory and motor deficits, often with systemic features 1
• Pain is a prominent feature in this inflammatory cause of neuropathy 1, 2
• May require nerve biopsy for definitive diagnosis, particularly when vasculitis is suspected 1

Diagnostic Approach

• Nerve conduction studies are essential to document large fiber involvement and to distinguish between axonal and demyelinating processes 1, 2
• Electromyography helps identify multifocal involvement patterns versus length-dependent patterns 1, 2
• In MMN, the hallmark finding is conduction block in motor nerves without sensory nerve abnormalities 3
• For MADSAM, electrodiagnostic studies show demyelinating peripheral neuropathy in multiple limbs 6

Treatment Considerations

• Treatment approaches differ based on the specific type of asymmetric/multifocal neuropathy 1
• For MMN, intravenous immunoglobulin is the first-line treatment and is effective in most patients 3, 4
• Immunosuppressive therapy may be required for inflammatory processes causing multifocal neuropathy 2
• Long-term maintenance therapy with immunoglobulins may be necessary but may not prevent slowly progressive axonal degeneration in MMN 3, 4

Clinical Pearls and Pitfalls

• Distinguishing asymmetric/multifocal neuropathies from motor neuron diseases (like ALS) is crucial as they differ in prognosis and treatment 3
• Asymmetric/multifocal neuropathies can be misdiagnosed as compressive neuropathies, leading to inappropriate treatment 6
• When patients exhibit progressive motor weakness and sensory deficits in more than one distal limb without specific findings of compressive neuropathy, clinicians should consider MADSAM 6
• The American Academy of Neurology recommends consideration of autonomic testing, skin biopsy, and nerve biopsy in select cases to establish the diagnosis and guide treatment 2