Rasch-built Overall Disability Scale for patients with chemotherapy-induced peripheral neuropathy (CIPN-R-ODS)
Introduction
Chemotherapy-induced peripheral neuropathy (CIPN) is a frequent neurological complication of cancer treatment.1 The overall incidence of CIPN is 3–7% in people treated with single agents but more severe neuropathy affects up to 30% of those treated with some currently approved drugs.1, 2 Moreover, peripheral neurotoxicity may occur in 38% of those treated with multiple chemotherapeutic agents often leading to dose adjustment or withdrawal of anti-neoplastic drugs.2 CIPN is difficult to treat and may severely affect patients’ daily functioning and quality of life.3 In light of potential therapeutic interventions for CIPN, effective outcome measures are mandatory. These outcome measures should fulfil all classical requirements, i.e. being simple, understandable, valid, reliable and responsive as well as meeting modern scientific objectives, i.e. having an interval or linear construct.4, 5, 6, 7
Outcome measures currently applied in CIPN are mostly ordinal based and some mix impairment and disability qualities.8, 9 Sum scores are generally calculated in multi-item measures assuming a linear pattern of the obtained scores, which is highly unlikely.10, 11 Therefore, data derived from these outcome measures should not be analysed using parametric statistics. The Rasch model overcomes these limitations.4, 5, 12 This method is based on the logical assumption that a person with a higher ability (in the current setting read: less disability) will have a higher probability of completing a more difficult daily item or task when compared to a person with lower ability. Scales based on Rasch analysis have the ability to locate both subjects’ ability and item difficulty along the same metric.4
The current paper presents the results of a Rasch-built CIPN specific outcome measure capturing activity limitations and participation restriction as part of the chemotherapy-induced peripheral neuropathy outcome measure standardization (CI-PeriNomS) study.13, 14
Section snippets
Patients and methods
After two consensus meetings between members of participating centres (20 neurologists and oncologists as part of the CI-PeriNomS study group), 281 CIPN patients aged 18 years and older were recruited from 19 European clinical centres between July 2008 and December 2010. Patients were considered eligible if they met inclusion/exclusion criteria of the CI-PeriNomS study as previously described.13, 14
Description of patients
A total of 281 patients were eligible. The median age was 63.9 years with an equal gender distribution. The commonest malignancy was colorectal cancer (42%). Patient characteristics are presented in Table 1 with further information as previously published.14
Data quality control
Data quality control was performed as the initial step in the analyses. Items scored as (3) ‘not applicable’ were entered as missing data. Items with an arbitrarily chosen cut-off of >15% missing values as well as subjects with >15%
Discussion
The current study provides a new scale, the CIPN-R-ODS, based on the Rasch methodology, measuring activity and participation in patients with stable CIPN.4, 5, 19 This outcome measure fulfilled all modern clinimetric requirements, showed invariance across items and persons (Fig. 5) and bypassed the disadvantages of ordinal based measures that have been previously used in CIPN.10 The constructed final CIPN-R-ODS demonstrated proper validity and reliability aspects. A high personal separation
Conflict of interest statement
Dr. Merkies had served on scientific advisory boards for Immune Globulin Intravenous CIDP Efficacy (ICE) trial, CSL Behring, and Novartis International AG; and had received research support from Talecris Biotherapeutics. The other authors declare no conflict of interest.
Acknowledgements
The patience and availability of the subjects who agreed to participate in the study are gratefully acknowledged. This work was not supported by any funding.
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