Progressive pseudorheumatoid dysplasia: A rare disease in the differential diagnosis of juvenile idiopathic arthritis

Introduction: Progressive pseudorheumatoid dysplasia (PPD) is an autosomal recessive skeletal disease. The responsible gene is called WISP3 and maps to the region 6q21 on chromosome 6. At the age of 3–6 years, stiffness and pain symmetrically involve finger joints first, later followed by hips and knees. Further symptoms are movement limitation, contractures and growth retardation. These symptoms are also found in juvenile idiopathic arthritis (JIA). Here we present one patient suffering from PPD. In this interactive poster, the different steps of this demanding differential diagnosis are explored.

Case report: An eight-year-old boy presented to our pediatric rheumatology clinic. At the age of six painful swelling in the proximal (PIP) and distal (DIP) interphalangeal joints had started bilaterally. Also progressive movement limitation in hips and knees without joint effusion was present. Laboratory parameters were normal; rheumatoid factor and anti-nuclear antibodies were negative. Finger x-rays showed non-specific increase of bone thickness. Treatment with NSAID relieved the pain but movement restriction progressed. JIA was suspected and MTX was started without success. A more extensive radiological examination then showed the so-called platyspondyly on lumbar spine x-ray and an enlarged epiphysis on hip x-rays. These pathognomonic findings led to the diagnosis PPD.

Discussion: The incidence of PPD is 1:1,000,000, the prevalence is 1:100,000. PPD is found more often in Mediterranean countries in children from consanguineous parents. In the third decade of life PPD has progressed to severe joint destruction, which requires joint replacement. To date causal therapy is not available. Pain and movement limitation are treated by NSAID and physiotherapy. Because of the similar presentation PPD is often misdiagnosed and treated as JIA, sometimes for years. Correct and early identification of PPD avoids futile trials of immunosuppressive therapy. However intensive psychological and physiotherapeutic treatment is mandatory.