Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)
Test in Focus
CIDP is a rare demyelinating condition that is often misdiagnosed. In this "Test in Focus" episode of the "Answers From the Lab" podcast, Divyanshu (Div) Dubey, M.B.B.S., describes Mayo Clinic Laboratories' new test that detects two antibodies — NF155 and CNTN1— that are known to cause CIDP but require different treatment compared with other CIDP cases. The new CIDP test builds upon the standalone NF155 test to further improve diagnosis and inform treatment decisions.
"Over time, two antibodies — NF155 and CNTN1 — have been validated to cause about 10% to 20% of all cases of CIDP," Dr. Dubey says. "Our new test folds in our standalone NF155 test with a new cell-based assay for CNTN1."
Early diagnosis of CIDP is key to preventing long-term disability. "A significant proportion of CIDP patients are misdiagnosed. By the time they come to our clinic, nearly all have some disability," Dr. Dubey says. "If the diagnosis isn't made early, the amount of disability they accrue goes up significantly. But I've had patients who've become totally symptom free with early diagnosis and appropriate treatment."
Confirming positivity for NF155 or CNTN1 optimizes treatment. The standard first-line treatment for CIDP is intravenous immunoglobulin, or IVIg. “However, despite early responses, patients with NF155 or CNTN1 often don’t respond as well to IVIg treatment in the long term.”
"Detection of these antibodies can identify patients who require more aggressive measures or alternative immunotherapy medications, such as rituximab," Dr. Dubey says. "The new CIDP diagnostic test not only helps us identify these antibody-positive cases. It also provides valuable information about how to treat these cases."
The new test uses a live cell flow cytometry assay to detect NF155 and a fixed cell-based assay to detect CNTN1. Those assays were chosen because they offered greater specificity and sensitivity compared with other methodologies. To avoid over-testing or under-testing for CIDP, Mayo Clinic Laboratories recommends that physicians first perform thorough clinical and electrodiagnostic studies to narrow the possible causes of a patient's neuropathy. "Following a phenotype-specific methodology reduces the chances of unnecessary test ordering," Dr. Dubey says.
He notes that most patients with CIDP present with lower-extremity weakness. Clues that CIDP might be NF155-positive include weakness predominantly in the ankles or below, neuropathic pain and significant sensory ataxia or inability to sense where the joints are positioned.
"These signs can be subtle, and it can be difficult to say with certainty which patients will be positive or negative for the tested antibodies," Dr. Dubey says. "In my practice, I lean towards ordering these tests consistently, given the importance of what the positive antibody results gives us — not just a diagnosis but also a path to treatment."
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This evaluation is useful in diagnostic work up of patients being evaluated for CIDP and related demyelinating peripheral neuropathies. This test should only be utilized in the appropriate clinical context.
Patient Preparation: For optimal antibody detection, we recommend blood drawing the specimen before initiation of immunosuppressant medication.
Preferred: Red top
Acceptable: Serum gel
Specimen Volume: 3 mL
Analytic time: 5 days
Days performed: Monday through Sunday at various times
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