Ultrasound of the nerves — An appropriate addition to nerve conduction studies to differentiate paraproteinemic neuropathies

• Ultrasound is appropriate to detect nerve enlargement in paraproteinemic PNP.
• Prominent enlargement occurs in CIDP-variants, focal enlargement in anti-MAG PNP.
• Axonal neuropathies associated with MGUS or multiple myeloma show no nerve enlargement.
• If identification by NCS is not possible, multifocal nerve enlargement warrants nerve biopsy.
• The ultrasound pattern sum score operationalizes the differentiation of PNPs.

ObjectiveTo investigate the use of peripheral nerve ultrasound (PNUS) in addition to nerve conduction studies (NCS) in the diagnosis of paraproteinemic neuropathies (PN).MethodsPNUS/NCS of predefined peripheral nerves and the 5th/6th cervical roots were performed in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) (+/− paraprotein), patients with anti-MAG neuropathy, and patients with neuropathy and multiple myeloma or monoclonal gammopathy of uncertain significance (MGUS) — summarized as M-protein associated neuropathies (MPAN) and compared to controls (+/− paraprotein).Results39 patients and 27 age-matched controls were included. Nerve enlargement was most marked in patients with CIDP, while in anti-MAG neuropathies enlargement was significant in the legs. In MPAN, no nerve enlargement is found regularly. However, in two cases, the diagnostic steps were influenced by the finding of multiple enlarged nerves and finally immunotherapy response was successfully initiated. By the use of the ultrasound pattern sum score (UPSS), differentiation of PN can be simplified.DiscussionDue to the heterogeneous findings in NCS, correct diagnosis of PN, and straightforward therapeutic decisions often may be controversial. Particularly in cases of M-protein related neuropathy, the finding of multiple nerve enlargements facilitates the decision for therapeutic approaches or nerve biopsy. The UPSS enables the distinction of different PN from each other.ConclusionThe use of an ultrasound quantification tool in addition to NCS facilitates a differentiation of PN.