INTEROBSERVER VARIABILITY IN THE ASSESSMENT OF NERVE FUNCTION IN LEPROSY PATIENTS IN ETHIOPIA

One of the major problems in leprosy is to detect any change in nerve function early enough so as to increase the chances of recovery and pr event disability. Several tests have been developed to assess nerve fu nction and are used in leprosy control programs worldwide, but they ar e frequently performed by different workers on different occasions and under variable conditions. In this study we investigated the variabil ity between different groups of observers in the assessment of nerve f unction in leprosy patients in Ethiopia. Sensory function was assessed by using a set of nylon monofilaments (NF) and a ball-point pen (BP), and motor function was assessed by using voluntary motor testing (VMT ). We also studied the variability between observers in the assessment of the clinical signs of neuritis. Duplicate measurements were perfor med in random order on 50 leprosy patients by two physio-technicians a nd on 50 other patients by two health assistants. The percent agreemen t between observers was calculated for each single nerve, and weighted kappa statistics were used to assess whether agreement was better tha n expected due to chance alone. Systematic differences between observe rs were evaluated using the Wilcoxon signed rank test. On sensory test ing, interobserver variability was found to be related to the training and experience of the observer, to the nerve tested, and to the neuro logical status of the patient.When tests were performed by physiotechn icians, we observed 32% to 58% agreement with the NF test and 71% to 8 4% agreement with the BP test, measured on different scales. After wei ghting for the scale difference, the agreement seemed comparable with these methods but the differences in measurements with the BP test wer e found to be dependent upon the neurological status of the patient. T he variability between observers differed according to the nerve teste d, and there was some evidence of systematic differences between obser vers with both methods. When performed by the health assistants, agree ment was between 34% and 46% with the NF and between 66% and 82% with the BP tests. After weighting for the scale difference, the agreement seemed comparable but the BP was not liable to the systematic differen ces seen in the NF results. These differences could be attributed to t he differences in the experience of the workers with these tests. With the VMT, small variability between observers was found for all nerves tested, except the facial nerve, when performed by both the physio-te chnicians and by the health assistants (72% to 98% agreement). Change agreement, however, could not be excluded since the ratings were extre mely homogenous. The assessment of neuritis signs was extremely variab le between observers (14% to 41% agreement), with evidence of a system atic difference between observers. Implications of these findings are discussed with the view to improving comparability of the nerve functi on tests under held conditions for early detection of nerve damage in leprosy patients.