Background and objectives: Diffuse idiopathic skeletal hyperostosis (DISH) is a bone formation disease in which only skeletal signs are considered in classification criteria. The aim of the study was to describe different phenotypes in DISH patients based on clinicoradiological features. Materials and Methods: We evaluated 97 patients who met the Resnick or modified Utsinger classification criteria for DISH and were diagnosed at our hospital from 2004 to 2015. Patients were stratified into: (a) peripheral pattern (PP)-Resnick criteria not met but presenting ≥3 peripheral enthesopathies; (b) axial pattern (AP)-Resnick criteria met but <3 enthesopathies; and (c) mixed pattern (MP)-Resnick criteria met with ≥3 enthesopathies. Statistical analysis was carried out to identify variables that might predict classification in a given group. Results: Fifty-six of the 97 patients included (57.7%) were male and 72.2% fulfilled the Resnick criteria. Applying our classification, 39.7% were stratified as MP, 30.9% as AP and 29.4% as PP. Clinical enthesopathy was reported in 40.2% of patients during the course of the disease. Sixty-eight patients were included in a comparative analysis of variables between DISH patterns. The results showed a predominance of women (p < 0.004), early onset (p < 0.03), hip involvement (p < 0.003) and enthesitis (p < 0.001) as hallmarks of PP. Asymptomatic patients were most frequently observed in AP (28.6%, MP 3.8%, PP 5.0%) while MP was characterized by a more extensive disease. Conclusions: We believe DISH has distinct phenotypes and describe a PP phenotype that is not usually considered. Extravertebral manifestations should be included in the new classification criteria in order to cover the entire spectrum of the disease.
Keywords: ankylosing hyperostoses; ankylosing spondylitis; diffuse idiopathic skeletal hyperostosis; enthesopathy; heterotopic; ossification; phenotype; vertebral.