Clinical, radiographic, and genetic diagnosis of progressive pseudorheumatoid dysplasia in a patient with severe polyarthropathy.

A 14-year-old boy presented with a 10-year history of the "sicca" form of seronegative juvenile idiopathic polyarthritis. Severely limited range of motion, pain, and capsular swelling in both small and large weight-bearing joints left him wheelchair-bound. Erythrocyte sedimentation rate and C-reactive protein were normal. Two-phase bone scan revealed tracer uptake of almost every joint at both early and late time points, indicating pathologic exudation and enhanced bone metabolism consistent with severe arthritis. However, radiographic studies revealed no erosive arthropathy but severe osteopenia, dysplastic bone changes, mega os trigonum, and platyspondylia. A magnetic resonance imaging (MRI) scan of the hips showed no signs of synovitis, pannus, or effusion but cartilage irregularities and subchondral cysts. These findings strongly suggested the diagnosis of progressive pseudorheumatoid dysplasia of childhood, an autosomal-recessive disorder of cartilage homeostasis. The patient carries a novel homozygous two-nucleotide deletion in exon 4 of the WISP3 gene. This genetic disorder is an important differential diagnosis of sicca polyarthritis.