Camptodactyly arthropathy coxa vara pericarditis syndrome

The camptodactyly arthropathy coxa vara pericarditis (CACP) syndrome is a rare condition principally characterised by

• congenital or early-onset camptodactyly and childhood-onset non-inflammatory arthropathy
• coxa vara deformity or other dysplasia associated with progressive hip disease 
• pericarditis

Pathology

The arthropathy is non-inflammatory. Synovial fluid in CACP syndrome is typically viscous, clear, honey-coloured, and low in cell count (representing its non-inflammatory nature). Synovial histology shows little or no mononuclear infiltration. Mild thickening of the synovium is often present, and giant cells are occasionally seen.

Genetics

It is thought to carry an autosomal recessive inheritance ³. A locus responsible for causing the CACP syndrome has been assigned to a 1.9-cM interval on human chromosome 1q25-31 by homozygosity mapping ^1,7.

Radiographic features

Plain film

Described features include

• camptodactyly : considered a universal feature, but may vary in severity and is not always obvious on radiographs
• coxa vara deformity in the pelvis with short femoral necks
• periarticular osteopenia : when detected in paediatric radiographs, this tends to be less marked than in those with juvenile idiopathic arthritis
• joint effusions may be apparent
• there can be smooth flattening of affected joint surfaces
• intraosseous fluid-filled herniations affecting the acetabulum that manifest on conventional radiographs as benign radiolucent acetabular lesions : considered a highly distinguishing feature ² 
• squaring or flattening of the metacarpal and phalangeal heads in the hands
• the cervical spine tends to normal throughout the course of the disease

Differential diagnosis

Some clinical and imaging features may overlap with that of

• juvenile idiopathic arthritis ²