Combined use of third generation anti-cyclic citrullinated peptide antibodies (aCCP3 IgG/IgA), rheumatoid factors (IgM, IgG and IgA isotypes), joints magnetic resonance imaging and ultrasonography in diagnosis of juvenile idiopathic arthritis

Objective: The purpose of the study was to assess the utility of aCCP3 IgG and aCCP IgG/IgA (third generation anti-cyclic citrullina-ted peptide antibodies) and rheumatoid factors isotypes (IgG, IgA, IgM) in the diagnosis of undifferentiated juvenile idiopathic arthritis.
Material and methods: The following inclusion criteria were used: age < 18 years, disease onset < 16 years, inflammation of at least one joint, disease/arthritis duration > 6 weeks, other diseases have been excluded during differential diagnosis. Rheumatoid factors isotypes IgM, IgG, IgA and aCCP3 IgG and aCCP IgG/IgA have been evaluated in sera of 11 patients. Ultrasound imaging of affected joints has been done in 6 cases. MRI was carried out only in 4 most uncertain cases of patients.
Results: There were no positive results of aCCP2 IgG (> 20 IU/ml) in examined group; the mean blood level was 4.85 j/ml. There were also no positive results of aCCP3 IgG/IgA (> 20 IU/ml) in tested cohort; the mean blood level was 1.91 IU/ml. Elevated levels of RF isotypes (> 6 IU/ml) have been found in studied group. Increased level (> 6 IU/ml) of IgM RF was found in 8 patients, mean level was 20.97 IU/ml; IgA RF mean level was 22.85 IU/ml, and positive results (> 6 IU/ml) were found in 6 patients; RF IgG isotype was present in 4 patients from tested group, and mean concentration amounted to 6.48 IU/ml. In 6 cases ultrasound of affected hands\' joints was performed; erosions have been demonstrated in 2 children. MR examination was carried out in 4 most uncertain cases and erosions have been demonstrated only in 1 child.
Conclusions: 1. Third generation anti-cyclic citrullinated peptide antibodies (aCCP3 IgG/IgA) assessment – with higher specificity and sensitivity than second generation antibodies (aCCP IgG) – has no utility in JIA diagnostic algorithm. 2. MRI and ultrasound of affected joints are helpful in the diagnosis of undifferentiated JIA due to ability to confirm signs impossible to demonstrate in standard X-ray imaging.