Inclusion Criteria:

• Male or female aged 18 years or older.
• Diagnosis of CIDP according to the 2021 EAN/PNS criteria; eligible phenotypes include typical CIDP, asymmetric CIDP (MADSAM/Lewis-Sumner syndrome), and pure motor CIDP. Pure sensory CIDP is excluded.
• Ability to undergo protocol assessments, including clinical evaluation, electrophysiological studies, nerve ultrasound, and blood sampling.
• Ability to provide written informed consent.
• Affiliation with a health insurance system or equivalent.

Group 1-specific criteria:

• Newly diagnosed CIDP.
• No previous immunomodulatory treatment for CIDP before baseline study assessment.
• Planned initiation of IVIg according to standard clinical practice.

Group 2-specific criteria:

• Established CIDP with persistent clinically relevant disability.
• Documented inadequate, partial, transient, or absent response despite adequate prior therapy, according to the final refractory disease definition.
• Stable treatment exposure before inclusion according to the final protocol.

Exclusion Criteria:

• Pure sensory CIDP.
• Alternative cause of neuropathy, including hereditary, metabolic, toxic, or other acquired neuropathies judged to better explain the clinical picture.
• Motor neuron disease, myopathy, neuromuscular junction disorder, or another neurological or neuromuscular condition interfering with clinical, electrophysiological, or ultrasound interpretation.
• CIDP mimic or alternative diagnosis.
• Active infection likely to influence study assessments.
• Active malignancy or other major systemic condition likely to confound biomarker interpretation.
• Concomitant autoimmune or inflammatory disease likely to materially influence cytokine or complement measurements.
• Severe psychiatric or cognitive disorder interfering with participation.
• Participation in another interventional trial when incompatible with the present protocol.
• Inability or unwillingness to comply with study procedures.