Laboratory Studies
See the list below:
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Test CSF on patients in whom chronic inflammatory demyelinating polyradiculoneuropathy is suspected. Protein level is increased significantly in 80% of patients (usually between 50 and 200 mg/dL, but can be higher); 10% of patients also have mild lymphocytic pleocytosis (< 50 cells) and increased gamma globulin (usually associated with HIV infection).
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CBC count, sedimentation rate, antinuclear antibody, biochemistry profile, and serum and urine immunoelectrophoresis are necessary to exclude important associated systemic disorders.
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In certain instances, genetic testing may be helpful. Examples include patients with positive family history, very insidious symmetric course of the disease, or some atypical features, including lack of treatment effect. In such cases, genetic testing for Charcot-Marie-Tooth disease might be indicated. Hereditary neuropathy with predisposition to pressure palsies can be suspected and tested for in some patients. Charcot-Marie-Tooth disease type 1X and adult-onset Charcot-Marie-Tooth disease type 1B have been confused with CIDP.
Imaging Studies
See the list below:
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Imaging studies can provide supportive evidence of CIDP.
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MRI of the spine with gadolinium enhancement may show enhancement of nerve roots.
Other Tests
EMG is a critical test to determine whether the disorder is truly a peripheral neuropathy and whether the neuropathy is demyelinating. Findings of a demyelinating neuropathy are as follows:
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Multifocal conduction block or temporal dispersion of compound muscle action potential, as shown in the image below
Electromyography of a patient with chronic inflammatory demyelinating polyradiculoneuropathy illustrating conduction block, temporal dispersion of compound muscle action potential, prolonged distal latencies, and slowed conduction.
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Prolonged distal latencies and dispersion of the distal compound motor action potential
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Variable conduction slowing to less than 70% of normal
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Absent or prolonged F wave latencies, as shown below
As the disease progresses, patients tend to develop secondary axonal degeneration.
Reports exist of a predominantly axonal neuropathy with clinical course and response to treatment similar to those of CIDP. Most cases of axonal neuropathy are not immune or inflammatory. However, some patients with an aggressive axonal neuropathy have been treated effectively with immunosuppressive and/or immunomodulatory therapy, raising the question of whether a chronic axonal inflammatory neuropathy, akin to the acute axonal variants of GBS, may be present. The relationship of these chronic axonal variants to CIDP is unclear.
Procedures
Peripheral (sural) nerve biopsy is considered as supportive evidence of CIDP.
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Consider biopsy for those patients in whom the diagnosis is not completely clear, when other causes of neuropathy (eg, hereditary, vasculitic) cannot be excluded, or when profound axonal involvement is observed on EMG.
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Some experts recommend biopsy for most patients prior to initiating immunosuppressive therapy, but more recent guidelines no longer recommend biopsy.
Histologic Findings
Tissue collected on biopsy of the sural nerve may demonstrate evidence of interstitial and perivascular infiltration of the endoneurium with inflammatory T cells and macrophages with local edema. Evidence exists of segmental demyelination and remyelination with occasional onion bulb formation, particularly in relapsing cases, like the one in the image below.
Electron micrograph of the peripheral nerve of a patient with chronic inflammatory demyelinating polyradiculoneuropathy. Note "onion bulb" formation in the myelin sheath of the nerve fibers due to continuous demyelination and remyelination. Courtesy of A. Sima, MD, Department of Pathology, Wayne State University.
Some evidence of axonal damage also is observed, with loss of myelinated nerve fibers. The inflammatory infiltrate with neutrophil infiltration is observed in only a minority of patients.
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Electromyography of a patient with chronic inflammatory demyelinating polyradiculoneuropathy illustrating conduction block, temporal dispersion of compound muscle action potential, prolonged distal latencies, and slowed conduction.
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Prolonged F wave latencies (normal is < 31).
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Electron micrograph of the peripheral nerve of a patient with chronic inflammatory demyelinating polyradiculoneuropathy. Note "onion bulb" formation in the myelin sheath of the nerve fibers due to continuous demyelination and remyelination. Courtesy of A. Sima, MD, Department of Pathology, Wayne State University.
