Tests
1st tests to order
nerve conduction studies
Test
All patients with a clinical suspicion of CIDP should have electrodiagnostic studies.
Diagnostic criteria are mainly based on finding a combination of slowed conduction velocities, prolonged distal latencies, prolonged F-wave latencies, and conduction block in one or more motor nerves. Sensory nerve conduction studies help support the diagnosis.[1]
A diagnosis of CIDP should not be completely excluded if a patient does not fulfill electrophysiologic criteria, as long as nerve conduction studies show some evidence of demyelination. Furthermore, especially for patients with CIDP variants, studying more than four motor nerves, utilizing proximal stimulation in the upper limbs, and including sensory nerves and somatosensory evoked potentials may improve sensitivity.[1] Nerve conduction studies should be repeated if doubt still exists about the diagnosis.
In purely sensory CIDP, nerve conduction studies may show only mild abnormalities not meeting typical electrodiagnostic criteria.[38][39]
In one study of patients referred to a tertiary care center for refractory CIDP, one of the main reasons for therapeutic failure was an incorrect alternative diagnosis. The importance of nerve conduction studies was emphasized, as many patients with alternate diagnoses (i.e., amyotrophic lateral sclerosis, idiopathic neuropathy, small-fiber neuropathy) had no demyelinating features and clinically lacked distal leg weakness, vibratory sensory loss, and widespread areflexia. CIDP mimics were also often misdiagnosed.[42]
Result
slow conduction velocities; prolonged distal latencies; prolonged F-wave latencies; conduction block in noncompressible sites
Tests to consider
cerebrospinal fluid (CSF) evaluation
Test
CSF analysis should be considered for patients with suspected CIDP when clinical and electrophysiologic testing is not definitively diagnostic. It is also advised if infection or lymphoproliferative disease is suspected or possible.[1]
In >90% of CIDP patients, CSF analysis typically shows albuminocytologic dissociation, consisting of elevated protein levels with a normal leukocyte count (<10 leukocytes/mm³). CSF protein levels of >45 mg/dL are abnormal; levels of >100 mg/dL are not unusual, and much higher levels can be found. However, cautious interpretation is needed, especially for patients with diabetes mellitus or spinal stenosis, and in young or older patients.[1][43][44][45]
Cell counts >10 leukocytes/mm³ should raise suspicion of infection or malignancy. Cell counts may be up to 50 leukocytes/mm³ in HIV infection.[46][47]
The sensitivity of CSF analysis for detecting CIDP variants is unknown.[1][48]
Result
albuminocytologic dissociation
nerve ultrasound
Test
For patients who fulfill clinical and electrodiagnostic criteria for a diagnosis of CIDP, imaging is not needed for diagnosis and therefore not recommended.[1] Nerve ultrasound is recommended as a diagnostic tool for adult patients who fulfill the diagnostic criteria for possible CIDP.[1]
The most common finding on ultrasound is multifocal nerve enlargement.[1][49][50] This can help to distinguish patients with CIDP from those with Charcot-Marie-Tooth disease type 1, in which nerves are usually diffusely enlarged.[51][52]
The presence of multifocal nerve enlargement correlates with electrodiagnostic findings.[50][53][78] One study showed motor nerve conduction velocity to be inversely correlated with cross-sectional area in nerve segments with electrodiagnostic evidence of demyelination.[53] Nerves with increased cross-sectional area were seen in patients with a more severe course of CIDP, as manifest by longer disease duration, lower Medical Research Council (MRC) sum score, higher Inflammatory Neuropathy Cause and Treatment (INCAT) score, and progressive disease.[53][54]
Diagnosis may be more likely if there is nerve enlargement of at least two sites in proximal median nerve segments/and or the brachial plexus (mimics must be excluded).[1]
Ultrasound may be used to assess treatment response.[55] Enlarged nerves may become smaller or normalize with remission of disease. Patients with active CIDP that is refractory to treatment will generally have enlarged nerves without significant change over time.[56]
There is a lack of evidence on the use of ultrasound in pediatric patients.[1]
Result
multifocal nerve enlargement of at least two sites in proximal median nerve segments and/or the brachial plexus; nerve enlargement is defined by cross-sectional area of median nerve >10 mm² at forearm, >13 mm² upper arm, >9 mm² interscalene (trunks), or >12 mm² for nerve roots
MRI spine and plexus with and without contrast
Test
For patients who fulfill clinical and electrodiagnostic criteria for a diagnosis of CIDP, imaging is not needed for diagnosis and therefore not recommended.[1]
MRI may be considered for adult patients when electrodiagnostic studies are inconclusive or who fulfill diagnostic criteria for possible CIDP, and when ultrasound is unavailable or unclear.[1]
Without gadolinium enhancement, hypertrophy of lumbosacral or cervical nerve roots or of the lumbosacral or brachial plexus is the most common abnormality. Rarely, hypertrophy involves cranial nerves; it is more common in longstanding disease with a relapsing-remitting course. Enhancement may be present and suggests inflammation.[1][57][79][80]
There is a lack of evidence on the use of MRI in pediatric patients.[1]
Result
enlargement and/or increased signal intensity of nerve root(s) on T2-weighted MRI sequences
clinical trial of therapy
Test
Most patients with CIDP will have a response to treatment with a first-line monotherapy (intravenous immune globulin, corticosteroids, or plasma exchange).[1][58][59][60] If the first monotherapy agent is ineffective, an alternative first-line agent should be tried.
Lack of at least a partial response to one or two first-line immunosuppressive agents should lead to consideration of an alternative diagnosis: for example, autoimmune nodopathies.
Result
clinical response
nerve biopsy
Test
Nerve biopsy is of limited diagnostic value, and is unnecessary for most patients.[3] It should only be performed in certain circumstances, mainly if the diagnosis is unclear and alternative diagnoses have not been fully excluded after nerve conduction studies, lumbar puncture, laboratory investigations, and imaging (if indicated). It may be helpful in cases where electrodiagnostic studies are inconclusive.[1][61] Biopsy should also be considered If there is a high suspicion of an infiltrative process such as seen in lymphoma, malignancy, amyloidosis, or sarcoidosis.[1]
Although the sural or superficial peroneal nerve is often biopsied, a biopsy from a clinically affected nerve will be more informative.[4][21]
Classic findings include unequivocal or predominant evidence of segmental demyelination, remyelination, or onion bulb formation by electron microscopy or teased fiber analysis. Demyelination often occurs paranodally or near nodes of Ranvier. Inflammatory cells (may or may not be present) are typically both epineurial and endoneurial.[1][3][6][41]
Evidence of axonal degeneration is common and includes axon loss and myelin ovoid formation.[6][21][22][40]
Result
demyelination and/or remyelination; axonal degeneration
enzyme-linked immunosorbent assay (ELISA) or Western blot to detect autoantibodies
Test
A small subset of patients have antibodies against nodal or paranodal proteins, which are usually of the IgG4 subclass; these include contactin-1 (CNTN1), neurofascin-155 (NF155), contactin-associated protein 1 (Caspr1), and neurofascin isoforms NF140/186.[62][63] Such patients are classified as having an autoimmune nodopathy, which presents with a distinct phenotype including rapid onset, ataxia, tremor, and poor response to intravenous immune globulin and corticosteroids.[1] Response to cyclophosphamide or rituximab has been reported.[64][65][66]
Result
may show anti-CNTN1, anti-NF155, anti-Caspr1, or anti-NF140/186 antibodies
other tests
Test
A range of tests is recommended to identify other potential conditions (e.g., HIV, diabetes mellitus, monoclonal gammopathy, malignancy, hepatitis, sarcoidosis, systemic lupus erythematosus, mixed connective tissue disease) or to establish an alternate diagnosis if the criteria for CIDP are not met.[1]
Result
positive result guides alternate diagnosis
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