Background/Purpose:   Progressive pseudorheumatoid arthropathy of childhood (PPAC, OMIM #208230) is a bone dysplasia caused by mutations in the WISP3 gene. Due to its presentation with joint stiffness and finger swelling, it is frequently misdiagnosed as polyarticular juvenile idiopathic arthritis (JIA). However, PPAC has some characteristics which distinguish it from JIA; early diagnosis avoids unnecessary treatments and allows adequate therapy for an optimum long-term outcome.

The objective of this study was to retrospectively document a single center cohort of PPAC and describe presentation and clinical course of this rare disease.

Methods: The database of the German Center for Pediatric and Adolescent Rheumatology was searched to identify all patients with a diagnosis of PPAC seen between 1997 and 2015. Clinical and molecular genetic data was extracted from patient files, and results were analyzed using descriptive statistics.                                                               

Results: 8 patients were included (6 male, 2 female), including 2 sibling pairs. Median age at presentation was 8 years (range 6 – 13 years), median follow-up was 8.5 years (range 3 – 18 years). Median age of first symptoms was 3 years (range 1 – 4 years). Four patients (50 %) were diagnosed as JIA prior to diagnosis of PPAC. Mutations in the WISP3 gene were detected in 5/5 tested patients. Typical symptoms at onset were abnormal gait (7/8 patients), swelling of the interphalangeal finger joints (4/8 patients) and muscular weakness (2/8 patients). All patients developed short stature with height below the 3rd percentile and an abnormally short trunk, mainly due to vertebral dysplasia which became apparent during elementary school in most cases. Other radiographic abnormalities included overgrowth of the epiphyses (8/8 patients), widening of the heads of the basal phalanges (8/8 patients) and malformation of vertebral bodies (8/8 patients). Functional impairment progressed in all cases, with severely impaired ambulation on last follow-up. Two patients regained longer walking distances after joint replacement of the hips, one patient also received knee arthroplasty. Avascular necrosis developed in 5/8 patients, involving the femoral head, the proximal tibia and the talus bone.

Conclusion: PPAC is frequently misdiagnosed as JIA, but history, typical symptoms and radiographs of the hands and spine can help to differentiate the two disease entities. Patients uniformly develop short stature and are at risk for avascular necrosis. Joint replacements can significantly improve function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/progressive-pseudorheumatoid-arthropathy-of-childhood-ppac-a-single-center-case-series/