Reliability of the El-Escorial criteria for the diagnosis of amyotrophic lateral sclerosis

Background. The El-Escorial criteria are widely used for the diagnosis of amyotrophic lateral sclerosis (ALS). Based on these criteria, the classification of the disease is made according to the level of diagnostic certainty (definite, probable, possible, suspected ALS, no ALS). The reliability of the El-Escorial criteria is unknown when the diagnosis of ALS must be assessed according to medical records, as is usually done with a registry of the disease. Methods. The reliability of the El-Escorial criteria in the hands of different investigators was tested in two subsequent steps, before and after training. First step: Using semi-structured forms, the information reported in the records of 20 patients with ALS and 19 patients with other clinical conditions (considered in the differential diagnosis) was examined separately by four neurologists (raters A through D, with decreasing clinical experience in the field of motor neuron disorders). For each patient, the raters had to make a diagnosis of ALS vs no ALS and, in patients with ALS, of definite, probable, possible and suspected ALS. The inter-rater agreement was tested on pairs of raters using the kappa statistics. Second step: To optimize the use of the El-Escorial criteria, the raters underwent training consisting in a discussion of the cases for which different diagnoses were made during the first step. The inter-rater agreement was further tested on the medical records of 98 additional cases, abstracted by the caring physicians participating in a regional registry of ALS. Results. Before training, the inter-rater agreement, measured by the weighted kappa, was poor for each pair (kappa 0.05 to 0.29). Concordance was at best modest at each diagnostic level. After training, agreement improved for each pair (kappa 0.52 to 0.88), with the lowest concordance for rater D. Agreement remained poor only at the lowest diagnostic level (ALS vs no ALS: kappa 0.08-0.36), mostly for rater D. Conclusion. The El-Escorial criteria are fairly reliable for the diagnosis of ALS according to medical records only after training and in the hands of the most experienced physicians. However, concordance is still poor when considering the lowest diagnostic level, which is relevant to the screening of early ALS cases.