Know Your Nerve Biopsy and Monoclonal Gammopathy Testing

Good Practice Points for Nerve Biopsy and Monoclonal Gammopathy Testing in CIDP Diagnosis

Nerve Biopsy:

• Nerve biopsy should not be a routine procedure for diagnosing CIDP.
• It should only be considered in specific circumstances, such as when CIDP cannot be confirmed with other diagnostic methods, or when there is little or no response to treatment.
• Skilled surgeons, neuropathologists, and specialized pathology laboratory facilities should be available for nerve biopsy.
• The low accuracy of nerve biopsy should be fully understood by the patient before undergoing the procedure.
• Current expert consensus on minimal standards for processing and evaluating nerve biopsies should be observed.
• Sural or superficial peroneal nerve biopsy is most common, but biopsy of a clinically affected nerve is more likely to provide useful information.
• Findings suggestive of CIDP on nerve biopsy may include thinly myelinated axons and small onion bulbs, demyelinated internodes in teased fibers, perivascular macrophage clusters, and supportive features of demyelination on electron microscopy.
• Clinical outcomes in patients with suspected CIDP, treated with immunomodulating agents after a biopsy-guided diagnosis of CIDP, have been successful.
• Nerve biopsies have poor sensitivity and specificity, and their contribution to the diagnosis is limited by these inaccuracies.
• The statement on nerve biopsy aims to reduce the number of unnecessary biopsies for suspected CIDP, given the low diagnostic accuracy and invasive nature.
• Sural nerve biopsy is associated with numbness in the area of innervation and other complications such as acute and chronic pain, allodynia, dysaesthesia, neuroma formation, infections, and wound dehiscence.
• Only a small number of carefully selected nerve biopsies will contribute to a more accurate diagnosis of CIDP and a lower probability of misdiagnosis.

Monoclonal Gammopathy Testing:

• Testing for serum monoclonal proteins is strongly advised in adult patients with a clinical suspicion of CIDP.
• Testing should include serum protein electrophoresis and immunofixation, spot urine immunofixation for light chains, and measurement of serum free light chains.
• If a gammopathy is found, further evaluation may be required, and haematology-oncology consultation should be strongly considered.
• Relevant monoclonal proteins may still have normal light chain and ratio measurements in SFLC assays.
• In patients with distal CIDP, repeat testing should be considered if no IgM paraprotein is found or anti-MAG antibody testing is negative.
• Vascular endothelial growth factor (VEGF) serum level testing is indicated in patients with a distal and painful CIDP phenotype, in whom a lambda light chain associated IgA or IgG paraprotein is found, when POEMS syndrome is suspected.