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.