Diagnostic Testing for Suspected CIDP
For suspected CIDP, perform nerve conduction studies and electromyography first to confirm demyelinating features, followed by MRI spine with contrast to rule out compressive lesions, CSF analysis showing elevated protein with normal cell count, and comprehensive serum testing to exclude mimickers. 1
Essential Electrodiagnostic Studies
Nerve conduction studies and electromyography are mandatory for CIDP diagnosis and must demonstrate demyelinating features including slowed conduction velocities, temporal dispersion, and conduction block. 1, 2 These studies are essential to confirm polyneuropathy, distinguish between axonal and demyelinating patterns, and document severity and distribution of nerve involvement. 3
Critical Imaging
MRI of the entire spine with and without contrast is essential to evaluate for nerve root enhancement and thickening, and critically to rule out compressive lesions and neoplastic causes that can mimic CIDP. 1 This is particularly important given that 47% of motor CIDP patients have associated inflammatory, infectious, or neoplastic conditions. 1
Cerebrospinal Fluid Analysis
CSF analysis should include cell count with differential, protein, glucose, cytology, and gram stain. 1 The classic finding in CIDP is elevated protein (often >45 mg/dL) with normal or mildly elevated white blood cells—termed cytoalbuminologic dissociation. 1, 2 Note that elevated WBCs can occur in immune checkpoint inhibitor-related cases. 1
Comprehensive Serum Testing
Perform the following serum tests to screen for reversible causes and CIDP mimickers: 1
- Blood glucose (to exclude diabetes)
- Serum B12 with metabolites (methylmalonic acid with or without homocysteine)—critical because serum B12 levels in the low-normal range may still indicate deficiency 3
- Serum protein immunofixation electrophoresis (to detect monoclonal gammopathies) 4, 5
- Complete blood count and erythrocyte sedimentation rate 3
- Comprehensive metabolic panel and thyroid function tests (TSH) 3, 1
- HIV testing 1, 5
- Consider vasculitic and autoimmune screening panel 1
Additional Testing for Specific Scenarios
- If acute-onset presentation: Consider serum antiganglioside antibody tests for Guillain-Barré syndrome subtypes 1
- If associated with immune checkpoint inhibitor therapy: Obtain troponin to evaluate myocardial involvement, ECG and echocardiogram if respiratory insufficiency or elevated CPK, and consider paraneoplastic autoantibody testing 1
- Metastatic bone surveys should be considered to evaluate for osteosclerotic myeloma 5
Key Diagnostic Pitfall to Avoid
Do not rely solely on laboratory tests without clinical correlation—laboratory tests alone have only a 37% diagnostic yield. 3 The diagnosis requires integration of clinical symptoms (progressive weakness and sensory loss evolving over at least 8 weeks), physical examination findings (distal and proximal weakness with areflexia), and electrodiagnostic confirmation of demyelination. 1, 2
When to Obtain Neurology Consultation
Early neurology consultation is recommended, particularly for grade 2 or higher symptoms, to guide electrodiagnostic interpretation and help differentiate CIDP from mimickers like amyloidosis, vasculitic neuropathy, or paraneoplastic syndromes. 1 The 8-week symptom duration distinguishes CIDP from Guillain-Barré syndrome. 1, 2
Tests with Limited Utility
Nerve biopsy is not routinely required if clinical, electrodiagnostic, and CSF findings are consistent with CIDP, though it can confirm demyelination with onion bulb formation and inflammatory infiltrates when the diagnosis remains uncertain. 1, 6 Cerebrospinal fluid analysis has low diagnostic yield except in suspected demyelinating polyneuropathies. 3