To describe the clinical and neurophysiological characteristics, as well as treatment outcomes of IgM-associated distal acquired demyelinating symmetric (DADS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) phenotypes.

IgM-associated-neuropathies are a heterogeneous group of presumably immune-mediated neuropathies with inconsistent immunotherapy responses.

Retrospective review of patients with DADS or CIDP IgM-associated-neuropathies, evaluated at the Mayo Clinic Rochester between 2004-2018.

100 patients (84:DADS, 16:CIDP) were identified; median presentation age was 67.5 years (range:41-89). Twenty-nine patients were female and 34/42 had positive myelin-associated glycoprotein (MAG) antibodies (anti-MAG-Ab+ve). Presenting complaints included sensory disturbance (n=99), weakness (n=36), gait-aid requirement (n=22) and pain (n=50). NIS was more severe at presentation amongst CIDP (median=40, range:4-65) than DADS patients (median=20, range:2-61.25). Nerve conduction studies demonstrated demyelinating features in both phenotypes; CIDP patients had proximal axonal loss, plus more frequent conduction block and temporal dispersion. Thermoregulatory sweat test was abnormal in 17/21 DADS and 3/7 CIDP patients. Composite autonomic severity scores were abnormal in 27/44 DADS (median=1, range:0-5) and 6/12 CIDP patients (median=0.5, range:0-6).

Sixty-two patients; 50 DADS (23 anti-MAG-Ab+ve) and 12 CIDP had follow-up>3 months. Median follow-up was 63 months (range:4-268) amongst DADS and 34 months (range:3-227) amongst CIDP patients. NIS progressed from 8 to 27 amongst DADS, and improved from 40.5 to 23 amongst CDIP patients.

Twenty-nine patients; 19 DADS (11 anti-MAG-Ab+ve) and 11 CIDP received immunotherapy. Median treatment duration was 17.5 months (range:3-179). Treatment resulted in improved median NIS-Total (41vs22, p=0.001) and NIS-Weakness (26vs8, p=0.001) amongst CIDP patients. Treatment nor anti-Mag-Ab status impacted NIS, NIS-sub-scores, or functional outcome in DADS patients.

IgM-associated DADS patients demonstrate slowly progressive clinical and electrophysiological abnormalities.  These were not impacted by immunotherapy or anti-MAG-Ab status. Autonomic and small-fiber abnormalities were mild but common amongst DADS patients. IgM-associated CIDP patients were more likely to respond to immunotherapy despite more severe disease at presentation.