Ultrasound of inherited vs. acquired demyelinating polyneuropathies

Abstract

We compared features of nerve enlargement in inherited and acquired demyelinating neuropathies using ultrasound. We measured median and ulnar nerve cross-sectional areas in proximal and distal regions in 128 children and adults with inherited [Charcot-Marie-Tooth-1 (CMT-1) (n = 35)] and acquired [chronic inflammatory demyelinating polyneuropathy (CIDP) (n = 55), Guillaine-Barre syndrome (GBS) (n = 21) and multifocal motor neuropathy (MMN) (n = 17)] demyelinating neuropathies. We classified nerve enlargement by degree and number of regions affected. We defined patterns of nerve enlargement as: none, no enlargement; mild, nerves enlarged but never more than twice normal; regional, nerves normal in at least one region and enlarged more than twice normal in at least one region; diffuse, nerves enlarged at all four regions with at least one region more than twice normal size. Nerve enlargement was commonly diffuse (89 %) and generally more than twice normal size in CMT-1, but not (p < 0.001) in acquired disorders which mostly had either no, mild or regional nerve enlargement [CIDP (64 %), GBS (95 %), and MMN (100 %)]. In CIDP, subjects treated within 3 months of disease onset had less nerve enlargement than those treated later. Ultrasound identified patterns of diffuse nerve enlargement can be used to screen patients suspected of having CMT-1. Normal, mildly, or regionally enlarged nerves in demyelinating polyneuropathy suggests an acquired etiology. Early treatment in CIDP may impede nerve enlargement.

Figure 1

Frequencies of nerve enlargement more than twice normal size in CMT-1 and acquired demyelinating polyneuropathies. Enlargement of nerve more than twice normal size at all sites is more common in CMT-1 (p<0.001) than in CIDP, GBS, or MMN. It occurs occasionally in CIDP.

Figure 2

Relationship between nerve size and pattern of nerve enlargement in CIDP and CMT-1. In CIDP, massively enlarged nerves (>400%) always have diffuse (type 3) enlargement while less enlarged nerves can have either regional (type 2) or diffuse enlargement. In CMT-1, nerve enlargement is nearly always diffuse. Patients with CIDP treated within three months of symptom onset have less enlarged nerves than those with longer disease duration before treatment. The dotted line marks the upper limit of normal.