Assessing the Benefit of Treatment in Chronic Inflammatory Demyelinating Polyneuropathy: the Challenges of Clinical Practice

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an immune-mediated motor and/or sensory disorder of the peripheral nerves which presents in various forms, resulting in functional neurological deficits.The prevalence of CIDP is low, of around 5 per 100,000 [1] but it is a disorder which responds to treatment, among which corticosteroids, intravenous immunoglobulins (IVIg) and plasma exchanges.The issue around evaluating effects of the treatment of CIDP is of great importance, both in avoiding deterimental indesirable effects as well as ensuring optimum cost-to-benefit ratio.As a result, effective, reliable and reproducible ways of assessing the benefit of treatment or the lack of it, are essential in clinical practice.In its typical form, CIDP presents with proximal and distal weakness of the four limbs.Sensory loss to large fibre modalities predominate.Motor deficits frequently represent the basis of disability.The evaluation of treatment effects has for many clinicians, been reliant on Medical Research Council (MRC) scores of groups of muscles, pre-and post-therapy.However, in sensory predominant forms strength scores are unhelpful.Use of disability measures are often not systematic and individualized goals, if used, may not infrequently be based on imprecise subjective descriptions, sometimes in retrospect.IVIg has not been demonstrated as effective on improving strength scores in meta-analyses of clinical trials performed, whereas they have been shown to improve disability scores.Different scales were however used in different trials and their clinical equivalence is not established.Transformation of various scales in a modified Rankin Scale equivalent allowed to demonstrate benefit from three pooled studies of 84 participants in the last Cochrane review [2].Disability scales are often considered by clinicians mainly as research tools and their implementation in day-today practice is variable.There are many reasons for this, including lack of time for detailed assessments, lack of familiarity with scales, as well as focus on traditional methods of evaluation which often include priority given to subjective patient descriptions.Also, the simple lack of interest by treating physicians, is a non-negligible factor.In recent years, emphasis has been put on the use of meaningful assessment tools, albeit essentially in the research arena, with increasing evidence of the inappropriateness of traditional MRC scores in the first instance.A new Rasch-built MRC grading has been proposed [3] but its clinical usage and uptake, has not been evaluated.The Inflammatory Neuropathy Cause and Treatment Group (INCAT) scale, consisting of an upper and a lower limb disability level component, represents a method used by many in practice [4].A newer version, the Overall Neuropathy Limitation Scale (ONLS), consisting of a slight variation of the leg score, has, similarly, been adopted by others [5].Despite poor content and structural validity, these scales are considered reliable and responsive [6].The minimum detectable change with the scale was however found greater than the minimal clinically important difference (MCID) which suggests suboptimal sensitivity to detect improvement in some subjects, compounded by low emphasis on proximal upper limb function and stamina-related tasks [6].In more recent years, a Rasch-built Overall Disability Scale (RODS) for Guillain-Barré syndrome, CIDP and gammopathy-related polyneuropathy has been developed, with construction of a 24-item scale consisting of tasks of increasing difficulty, with a conversion into a centile metric