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We need greater vigilance, with more rigid or standard criteria for atypical CIDP
Chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated neuropathy progressive for more than 2 months, including several clinical subtypes.1 2 In 1975, Dyck et al 3 described the classical prototype of CIDP, and emphasised that a prominent clinical feature is weakness of the proximal and distal muscles about equally which is very rarely seen in other nerve length-dependent polyneuropathies. They proposed that such non-length-dependent pattern was caused by lesions in the nerve roots, presumably affecting the long and short nerves equally. From a current viewpoint, the assumption is partly correct; in classical CIDP, the distal nerve terminals and nerve roots, where the blood–nerve barrier is anatomically deficient, are predominantly affected, evidenced by electrodiagnostic and neuroimaging findings.4
However, later in 1991 the research criteria proposed by the American Academy of Neurology (AAN) defined clinical inclusion criterion as ‘motor-sensory dysfunction of more than one limb’.5 According to the AAN criteria, any acquired demyelinating neuropathies, such as predominantly distal (distal acquired demyelinating symmetric (DADS)), asymmetric/multifocal (Lewis-Sumner syndrome), pure motor, or pure sensory neuropathy or even multifocal motor neuropathy could be included in CIDP.
In 2005, the Joint Task Force of the European Federation of Neurological Societies and the Peripheral Nerve Society (EFNS/PNS) reasonably classified CIDP into clinical subtypes; the classical CIDP proposed by Dyck et al 3 was categorised as ‘typical CIDP’, and ‘atypical CIDP’ included Lewis-Sumner syndrome, DADS and other variants.6 Then several studies have reported the frequency and features.
In their JNNP paper, Donuddu and colleagues7 reported the results of an Italian multicentre database study involving a total of 460 patients with CIDP . At the time of registration more than 1 year after onset, 82% of them had typical CIDP, and the remaining 18% had atypical CIDP. This is the largest study on atypical CIDP, and therefore data are informative. The atypical CIDP included DADS (7% of the total patients with CIDP), Lewis-Sumner syndrome (4%), pure motor (4%) and pure sensory CIDP (3.5%). The study also showed that patients with DADS or Lewis-Sumner syndrome were less responsive to immunoglobulin therapy, providing an important insight into the management of patients with CIDP according to clinical subtypes.
A surprising finding in this study was that at the time of ‘initial’ diagnosis, 39% of the whole patients with CIDP were classified with atypical CIDP. Assuming that 18% were finally categorised as atypical CIDP, 53% changed the classification from ‘atypical’ to ‘typical’ CIDP. Because each CIDP subtype presumably has different pathophysiology,8 9 we think that the transition is unlikely, and the data represent difficulty in the clinical definition of CIDP. For example typical CIDP is defined as having proximal as well as distal muscle weakness, but it is unclear whether this means equal involvement of the proximal and distal muscles, or merely the presence of slight proximal muscle weakness. Similarly the asymmetry in Lewis-Sumner syndrome and distal predominance in DADS are not defined clearly. Moreover, any variants could show proximal muscle weakness with disease progression.
Each atypical CIDP subtype, and even typical CIDP, should be more strictly defined clinically. The European Academy of Neurology/PNS (formerly EFNS/PNS) Task Force has just started the second revision of the CIDP guideline and is expected to answer this simple but critical question. This should greatly improve the quality of research and clinical trials for typical and atypical CIDP.10 11
Contributors SK wrote the draft, and SM and MM made revisions.
Funding This work was supported in part by the Health and Labour Sciences Research Grant on Intractable Diseases (Neuroimmunological Diseases) from the Ministry of Health, Labour and Welfare of Japan.
Competing interests None declared.
Patient consent Not required.
Provenance and peer review Commissioned; internally peer reviewed.