The International CIDP Outcome Study (ICOS): An Update

Introduction:

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a rare immune-mediated polyneuropathy with a heterogenous presentation and response to treatment. The International CIDP Outcome Study (ICOS) is investigating the clinical presentation of CIDP, and its pathogenesis, diagnostic and prognostic biomarkers, response to treatment and long-term clinical course and outcome.

Methods:

ICOS is a prospective, observational, multicenter study in which three Dutch university CIDP expert centers collaborate (Amsterdam UMC, UMC Utrecht, Erasmus MC). Patients fulfilling the EFNS/PNS 2010 criteria for CIDP are eligible to participate. Clinical, diagnostic and treatment data are collected, as well as biomaterials (DNA, cerebrospinal fluid, and serial serum samples). For the first two years, follow-up visits are scheduled every 6 months, and then annually thereafter. Validated disability scales and patient reported outcomes, such as RODS, R-FSS, and EQ-5D-5L, are assessed at each visit.

Results:

By 1st of January, 2023, a total of 300 patients are enrolled (63% men, median age at diagnosis of 59 years). Acute-onset CIDP (nadir within 8 weeks from disease onset) is reported in 30% of patients. At study entry, 71% of patients are diagnosed with typical CIDP, whilst 28% of patients have a variant of CIDP (asymmetric 15%, predominant motor 6%, -sensory 3% or predominant distal involvement 4%). At study entry, 44% of patients treated with IVIg reported end of dose symptoms, which decreased to 23% at

12 months and 14% at the 24 month follow-up. Recruitment closed on 15 March 2025, so it is no longer possible to include new patients.

Conclusions:

ICOS aims to optimize the diagnostic process and treatment strategies for CIDP, in order to improve long-term outcome. The decrease in end of dose symptoms in patients treated with IVIg during follow-up might result from dose adjustments or stabilization of disease symptoms. Further harmonization of study protocols will allow close collaboration of ICOS with other registries, such as IncBase.