Two distinct patterns of ankylosing spondylitis in Moroccan patients

Ankylosing spondylitis (AS) is characterised by a geographic differences in terms of prevalence and clinical expression of the disease. The aim of our study was to describe the actual features of AS in Morocco and we wanted to examine a large population of patients for evidence of phenotypic clustering that could suggest the presence of distinct clinical entities. We investigated 117 patients with a diagnosis of primary AS according to the modified New York criteria. All patients were evaluated according to a standardised data collection form, including demographic variables and disease history with clinical and radiological features. To analyse our data and try to individualise clinical subsets, we applied a two-step cluster analysis using log-likelihood distance measures. Patient’s mean age at onset was 25.51 ± 10.8 year. The mean BASDAI and BASFI score was 33.5 ± 20.3 and 38.9 ± 27.5, respectively. Radiographic damage was present in 99.1% of the subjects and radiographic hip involvement in 47.3%. Only 52.6% of patients had been treated with disease modifying antirheumatic drugs. Cluster analysis detected two distinct populations within the data set. Statistically significant differences were found between the two groups particularly concerning activity of the disease, age at onset and the hygienic conditions. Our study revealed that the Moroccan AS was active and severe and suggested that the age at onset and the precarious hygienic level has the greatest capacity to predict activity and severity of the disease.