Nerve Ultrasound Performances in Differentiating POEMS Syndrome from CIDP

Chronic inflammatory demyelinating polyneuropathy (CIDP) and polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome are both acquired demyelinating polyneuropathies. We aim to explore the different features of ultrasonographic changes between CIDP and POEMS syndrome. Nerve ultrasonographic studies were performed in 120 patients with CIDP and 34 patients with POEMS syndrome. Cross-sectional areas (CSAs) were measured on the bilateral median nerve, ulnar nerve, and brachial plexus. Nerve conduction studies were performed on median and ulnar nerves to detect motor conduction blocks (CBs). CSAs at all sites were larger in patients with CIDP and POEMS syndrome than in healthy controls. Maximal CSA (median (min to max)) was 14 (6-194) mm² for median nerve, 9 (4-92) mm² for ulnar nerve, and 14 (7-199) mm² for brachial plexus in CIDP and 11 (8-16) mm² for median nerve, 8.5 (6-13) mm² for ulnar nerve, and 14 (10-20) mm² for brachial plexus in POEMS syndrome. The ratio of maximum/minimum CSA of the median nerve was significantly larger in CIDP (2.8 ± 2.8) than in POEMS syndrome (1.7 ± 0.3). CBs or probable CBs were detected in 60 out of 120 CIDP patients but in none of the POEMS syndromes. For distinguishing CIDP and POEMS syndrome, a two-step protocol using CB and maximum/minimum CSA of the median nerve yields a sensitivity of 93% and a specificity of 79%. In conclusion, compared with CIDP, nerve CSA enlargement was more homogeneous along the same nerve in individual POEMS patients, as well as among different POEMS patients. The addition of nerve ultrasound to nerve conduction studies significantly improves the differential diagnosis between the two diseases.