International chronic inflammatory demyelinating polyneuropathy outcome study (ICOS): Protocol of a prospective observational cohort study on clinical and biological predictors of disease course and outcome.

Chronic inflammatory demyelinating polyneuropathy (CIDP) is a heterogeneous immune-mediated disorder with extensive variation in clinical presentation, electrophysiological phenotype, treatment response and long-term outcome. This heterogeneity may reflect the existence of distinct subtypes of CIDP with a different pathogenesis that require personalized treatment. The International CIDP Outcome Study (ICOS) is a prospective, observational, multicenter cohort study that aims to describe this variation and to define clinical and biological determinants and predictors of these subtypes, disease activity, treatment response and outcome. All patients fulfilling the European Federation of Neurological Societies/Peripheral Nerve Society 2010 diagnostic criteria for CIDP can participate, independent of age, duration and severity of the disease or treatment. We collect data on the clinical presentation, diagnostics, validated clinical outcome measures, (response to) treatment, and we collect biomaterials (DNA, cerebrospinal fluid and serial serum samples). We aim to include at least 1000 CIDP patients with a follow-up of at least 2 years. ICOS started in November 2015 in three academic medical centers in The Netherlands and by October 2018 169 patients are included: 69 new and 100 prevalent cases. ICOS is based on the format of the International Guillain-Barré syndrome (GBS) Outcome Study (IGOS). Dutch centers are invited to participate in ICOS that will continue as an independent national registry. International centers will be able to collect data and biomaterials according to the ICOS protocol by using the optional ICOS module within the INCbase infrastructure. ICOS will help to standardize the collection of data and biosamples for future research in CIDP.