Which variant of Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) presents with preserved reflexes?

Multifocal Acquired Demyelinating Sensory and Motor Neuropathy (MADSAM) is the CIDP Variant with Preserved Reflexes

The MADSAM variant of Chronic Inflammatory Demyelinating Polyneuropathy (CIDP), also known as Lewis-Sumner syndrome, is characterized by preserved reflexes in areas not affected by weakness, unlike typical CIDP where reflexes are generally reduced or absent throughout. 1, 2

Understanding CIDP Variants and Reflex Patterns

• Typical CIDP presents with symmetric proximal and distal weakness, sensory deficits in both upper and lower extremities, and globally reduced or absent deep tendon reflexes 2
• MADSAM/Lewis-Sumner syndrome is an atypical CIDP variant characterized by asymmetric multifocal pattern of motor and sensory loss, with reflexes typically preserved in unaffected areas 3, 4
• In MADSAM, the asymmetric distribution of lesions results in multiple mononeuropathy or asymmetric polyneuropathy, with demyelination primarily affecting nerve trunks rather than terminals and roots 2
• While typical CIDP shows reduced reflexes throughout, MADSAM patients maintain normal reflexes in areas not affected by the multifocal process 3, 2

Distinguishing Features of MADSAM from Other CIDP Variants

• MADSAM presents with asymmetric limb weakness and sensory loss in the distribution of individual peripheral nerves, unlike the symmetric presentation of typical CIDP 3, 4
• Multifocal Motor Neuropathy (MMN), another CIDP variant, differs from MADSAM by having purely motor involvement without sensory symptoms, though it may also have preserved reflexes in unaffected areas 5, 3
• Electrophysiologically, MADSAM shows conduction block and other features of demyelination in nerve conduction studies, but in a multifocal pattern rather than the diffuse pattern seen in typical CIDP 3, 2
• MADSAM's pathophysiology likely involves cellular immunity breaking down the blood-nerve barrier at sites of conduction block, whereas typical CIDP involves antibody-mediated demyelination 2

Clinical Implications and Diagnostic Approach

• Recognizing MADSAM is crucial as it may require different treatment strategies compared to typical CIDP 2, 6
• Nerve biopsy may be particularly useful in evaluating atypical forms of CIDP like MADSAM, as these variants may have distinctive pathological features 7
• MRI of the brachial or lumbosacral plexus can help identify focal or diffuse peripheral nerve abnormalities in CIDP variants 1
• The presence of preserved reflexes in a patient with otherwise typical features of demyelinating neuropathy should raise suspicion for MADSAM rather than typical CIDP 3, 2

Treatment Considerations

• MADSAM typically responds to immunomodulatory treatments, particularly intravenous immunoglobulin (IVIG) 4, 6
• Recent studies have demonstrated the efficacy of both subcutaneous and intravenous immunoglobulin as maintenance therapy for CIDP variants 6
• Refractory cases may require newer immunomodulating drugs 6
• The different immunopathogenesis of MADSAM compared to typical CIDP may explain potential differences in treatment response 2

Common Pitfalls in Diagnosis

• MADSAM may be misdiagnosed as motor neuron disease due to asymmetric weakness, but the presence of sensory symptoms and conduction block on nerve conduction studies helps differentiate 5, 3
• The preserved reflexes in MADSAM can lead to confusion with other neurological conditions where reflexes are typically normal 3, 2
• Relying solely on reflex examination without comprehensive electrophysiological testing may lead to misdiagnosis, as conduction block is a key diagnostic feature of MADSAM 3, 4
• Failure to recognize MADSAM as a distinct entity from typical CIDP may result in suboptimal treatment approaches 2, 6