How not to Misdiagnose the Mild Forms of Mucopolysaccharidosis and Juvenile Idiopathic Arthritis.

AIMS: The similarity between mucopolysaccharidosis (MPS) patients and juvenile idiopathic arthritis (JIA) leads to ineffective and needless anti-rheumatic treatment and delayed initiation of enzyme-replacement therapy, the early start of which is crucial for diminishing the disease progression and yielding better outcomes.

BACKGROUND

The prevalence of joint involvement in the attenuated forms of MPS leads to the JIA misdiagnosis, especially in patients without distinctive facial dysmorphic features.

OBJECTIVE

Our study aimed to compare mild forms of MPS and JIA and create a diagnostic score helping to differentiate both conditions.

METHODS

41 patients with mild forms of different types of MPS and 255 JIA patients with polyarthritis were included in the retrospective study. The routine clinical and laboratory features were used for the comparison analysis.

RESULTS

The main features of the MPS cohort were younger age at the disease onset, lower weight and height lower inflammation, and higher number of affected joints compared to JIA patients and involvement in the organs and system, specific for MPS. The majority of the patients had similar C-reactive protein levels. At least two extra-articular features with polyarticular involvement were the main discriminating factors for both conditions. The sum (>38) of the following criteria:ESR< 12 mm/h (38 points), growth delay (height ≤ -2.0 SD; 20 points), age of joint involvement < 1.0 years (24 points), male sex (15 points), and involvement of both elbows with limited range of motion (29 points) can help in the differentiation If a patient had no extra-articular features, typical for MPS. The specificity and sensitivity of this model are 91.0% and 92.7% respectively.

CONCLUSION

This diagnostic algorithm might increase the suspicion of MPS and should be added to routine testing not miss the mild form of MPS inside JIA. Early diagnosis of mild cases allows for the initiation of treatment in patients with MPS at an earlier stage, which can significantly improve their daily functioning and quality of life.