Differential diagnosis in rheumatic diseases applies to many different diseases, including metabolic disorders. Mucopolysaccharidosis (MPS) disorders are a clinically heterogeneous group of genetically determined diseases classified as lysosomal storage diseases (Table I, Fig. 1). The cause of each of the seven known mucopolysaccharidoses is deficient activity of enzymes involved in the catabolism of glycosaminoglycans (GAGs) leading to gradual GAG accumulation in cells and tissues of the body. Symptoms affecting the osteoarticular system are common in the course of these disorders. Destructive changes in the synovium of joints, cartilage, bone and periarticular soft tissues are secondary to the accumulation of GAGs in these structures (Table II, Figs. 2, 3). Joint pain and/or limitation of motion are often the first symptom reported already in the first decade of life, due to which the patient is referred to a rheumatologist. In studies of diagnostic imaging changes described as dysostosis multiplex are typical. Due to advances in the treatment of these diseases, early diagnosis and differentiation is important, which may be particularly difficult in attenuated forms (Tables III, IV, Fig. 4).