Abstract: 
Chronic inflammatory demyelinating polyneuropathy (CIDP) is a chronic immune-medi-ated peripheral form of polyneuropathy. No reliable diagnostic biomarkers are available by which to make the diagnosis of CIDP. As a result, diagnosis of the condition can be challenging. Many patients are not recognized early in the disease course, and on the other end of the spectrum both establishing early and accurate diagnosis as well as avoiding misdiagnosis and overtreatment. Identification of the hallmark clinical, electro-physiological, and laboratory features of the disease are critical to facilitate rapid diagno-sis, while an understanding of diagnostic pitfalls can help prevent misdiagnosis. Since the original description of CIDP in the 1970s, over 15 sets of diagnostic criteria have been proposed. The criteria published in 2021 by the European Academy of Neurology /Peripheral Nerve Society (EAN/PNS) were developed for use during routine clinical care and are available in the public domain. These criteria provide clinicians with an invaluable resource by which the data collected during the evaluation of the patient with possible CIDP can be interpreted. One point of importance that bridges diagnosis to treatment is objectification of the treatment response. Interpretation of how patients respond to treatment drives both long-term treatment paradigms and the diagnosis at which these treatments are aimed. Although no approach is perfect, utilization of strength impairment and disability outcomes in clinical practice can help unravel the difficulties in interpreting response to treatment. Just as improvement in these outcomes is considered diagnosti-cally supportive, the absence of objective benefit argues against it and should prompt reconsideration of a CIDP diagnosis.

R.A.L. has served as a consultant for Argenx, Biotest, CSL Behring, Grifols, Momenta (J&J), Sanofi Genzyme, Pfizer, and UCB; has received speaker honoraria and served on advisory boards for Akcea, Alnylam, CSL Behring, Grifols, and Medscape; and has received royal-ties from Up to Date. J.A.A. has served as a consultant for Alexion, Momenta (J&J), Sanofi, Argenx SE, and has received speaker honoraria and served on advisory boards for Akcea, Alexion, CSL Behring, Argenx, Takeda, and Grifols. All conflicts of interest have been resolved according to ACCME standards.