camptodactyly - arthropathy - coxa vara - pericarditis ( cacp ) syndrome is a genetic disorder caused by mutation in the proteoglyacn prg4 gene on chromosome 1 ( online mendelian inheritance in man omim number 208250 ) . the syndrome is characterized by congenital or early - onset camptodactyly and childhood - onset of non - inflammatory arthropathy , coxa vara deformity , or other dysplasia associated with progressive hip disease and non - inflammatory pericardial effusion . it has an autosomal recessive mode of inheritance and the causative gene is located on chromosome band 1q25 - 31 . we present a case of a female child who presented with early onset camptodactyly , non - inflammatory arthropathy , short femoral necks , with distinctive features on biopsy and magnetic resonance imaging ( mri ) , without pericarditis or pericardial effusion . a 3-year 3-month - old child presented with a 4-month history of swelling of both knees and wrists . the parents also stated that they had noticed bent fingers for nearly one and a half years . on examination , the patient had camptodactyly of the fingers with swelling of both knees and wrists without restricted motion or signs of inflammation like erythema or tenderness . systemic examination showed no evidence of fever , lymphadenopathy , skin rash , or other systemic features . routine blood work - up revealed normal hemogram , erythrocyte sedimentation rate ( esr ) and c - reactive protein ( crp ) with negative antinuclear antibody ( ana ) . anteroposterior ( ap ) radiograph of pelvis revealed a broad short femoral neck and coxa vara [ figure 1 ] . x - ray of the knee revealed bilateral effusions with osteopenia and no erosions [ figure 2 ] . mri of the hip showed a large joint effusion and intraosseous fluid - filled herniations affecting the acetabulum with intra - articular connection [ figure 3a ] . the synovium was mildly thickened and showed enhancement , better appreciated on the left side [ figure 3b ] . conspicuously , t9/21/2013here was absence of cartilage destruction . knee mri showed large amount of joint fluid [ figure 4a ] with mildly thickened enhancing synovium [ figure 4b ] . anteroposterior radiograph of pelvis shows smooth flattening of femoral heads with irregular acetabulae ( arrows ) . plain ap radiograph of both knees shows periarticular osteopenia , apparent widening of the joint space the result of effusions ( arrow ) and enlargement of the epiphyses secondary to the hyperaemia ( double arrows ) . coronal stir image of hips ( on 3 t system ) shows large bilateral joint effusions . note the intra - osseous acetabular herniations communicating with the effusions ( arrows ) and ( b ) 3-year 3-month - old girl child with cacp syndrome . coronal t1-weighted image of hips ( on 3 t system ) obtained after administration of gadolinium shows rim enhancement of joint capsule ( better appreciated on the left side ) and of walls of intraosseous herniations ( arrows ) . coronal stir image of both knees ( on 3 t system ) shows large effusions . small intraosseous cysts are identified along the medial femoral condyle ( arrows ) and ( b ) 3 year 3 month old girl child with cacp syndrome . coronal t1 weighted of both knees ( on 3 t system ) shows effusion with mildly thickened synovium ( arrows ) . ancillary investigations like-2 dimensional ( 2d ) echocardiography carried out did not reveal effusion or pericarditis . cacp syndrome , first described in 1984 , is characterized by congenital or early - onset camptodactyly , childhood - onset non - inflammatory arthropathy associated with synovial hyperplasia , progressive coxa vara deformity , and non - inflammatory pericardial or pleural effusion . it is an autosomal recessive condition caused by loss of function mutations in the proteoglycan-4 ( prg4 ) gene , leading to absence of lubricin in the synovial fluid and accumulation of synovial fluid in the joint spaces . marcelino et al . , ( 1999 ) identified the prg4 gene within the chromosome 1q25-q31 as the critical region for the autosomal recessive cacp syndrome ( phenotype number 208250 ) . children with cacp syndrome often present with camptodactyly ( bent fingers ) and swollen joints with preserved range of motion without other signs of inflammation . camptodactyly is a universal finding in patients with cacp and is usually bilateral and congenital , but may develop in early childhood . squaring or flattening of the metacarpal and phalangeal heads can be seen on radiograph of the hand . arthropathy principally involves large joints such as elbows , hips , knees , and ankles . the hallmark of this condition is intra - osseous fluid - filled herniations affecting the acetabulum that is seen on conventional radiographs as benign radiolucent acetabular lesions . there is mild synovial thickening and rim - like enhancement of the fluid - filled bursae . the presence of coxa vara is variable with studies reporting figures between 50% and 90% . pericarditis is a variable finding and has been reported in up to 30% of cacp , and it may be mild and self - limited . laboratory investigations including esr , crp , and full blood count are normal in patients with cacp syndrome . synovial fluid in this condition is clear , honey - coloured , and low in cell count . the synovial histology shows little or no mononuclear infiltration , but there is a typically described multinucleated giant cells infiltration . giant cells have been identified as macrophage in origin based on cd68 expression and electron microscopic features of macrophages . studies involving synovial fluid examination from a patient with cacp showed that hyaluronic acid molecules adopted an extended and more rigid conformation , suggesting that synovial fluid lacking lubricin would be less able to dissipate the energy of impact that occurs during motion . jay et al . , ( 2007 ) concluded that lubricin provides a chondroprotective feature to synovial fluid that is distinct from the role lubricin plays at the cartilage surface as a boundary lubricant . this condition must be distinguished from juvenile idiopathic arthritis since the management of juvenile idiopathic arthritis ( jia ) requires anti - inflammatory drugs , often with methotrexate and steroids owing to the inflammatory nature of the disease , whereas cacp syndrome does not respond to these drugs and is treated symptomatically and with physiotherapy . jia has been classified by the international league of associations for rheumatology ( ilar ) into : 
 systemic onset juvenile rheumatoid arthritis ( jra ) : arthritis in one or more joints with or preceded by fever of at least 2-weeks duration , documented daily for at least 3 days accompanied by one or more of the following : evanescent ( non - fixed ) erythematous rash , generalized lymph node enlargement , hepatomegaly and/or splenomegaly , and serositisoligoarthritis : arthritis affecting one to four joints during the first 6-months of the disease , with the persistent type affecting not more than four joints throughout the disease course , while the extended type affects a total of more than four joints after the first 6-months of the diseasepolyarthritis ( rheumatoid factor ( rf ) negative ) : arthritis affecting five or more joints during the first 6-months of disease ; rf is negativepolyarthritis ( rf positive ) : arthritis affecting five or more joints during the first 6-months of the disease ; two or more tests for rf at least 3-months apart during the first 6-months of disease are positivepsoriatic arthritis : arthritis with psoriasis or arthritis and at least two of the following : dactylitis , nail pitting ( onycholysis ) or psoriasis in a first - degree relativeenthesitis related arthritis : arthritis with enthesitis or only arthritis / enthesitis with at least two of the following : presence of or a history of sacroiliac joint tenderness and/or inflammatory lumbosacral pain , presence of human leukocyte antigen ( hla - b27 ) antigen , onset of arthritis in a male over 6-years of age , acute anterior uveitis , or history of ankylosing spondylitis , enthesitis - related arthritis , sacroiliitis with inflammatory bowel disease , reiter 's syndrome or acute anterior uveitis in a first - degree relativeundifferentiated arthritis : arthritis that fulfills criteria in no category or in two or more of the above categories . 
  systemic onset juvenile rheumatoid arthritis ( jra ) : arthritis in one or more joints with or preceded by fever of at least 2-weeks duration , documented daily for at least 3 days accompanied by one or more of the following : evanescent ( non - fixed ) erythematous rash , generalized lymph node enlargement , hepatomegaly and/or splenomegaly , and serositis oligoarthritis : arthritis affecting one to four joints during the first 6-months of the disease , with the persistent type affecting not more than four joints throughout the disease course , while the extended type affects a total of more than four joints after the first 6-months of the disease polyarthritis ( rheumatoid factor ( rf ) negative ) : arthritis affecting five or more joints during the first 6-months of disease ; rf is negative polyarthritis ( rf positive ) : arthritis affecting five or more joints during the first 6-months of the disease ; two or more tests for rf at least 3-months apart during the first 6-months of disease are positive psoriatic arthritis : arthritis with psoriasis or arthritis and at least two of the following : dactylitis , nail pitting ( onycholysis ) or psoriasis in a first - degree relative enthesitis related arthritis : arthritis with enthesitis or only arthritis / enthesitis with at least two of the following : presence of or a history of sacroiliac joint tenderness and/or inflammatory lumbosacral pain , presence of human leukocyte antigen ( hla - b27 ) antigen , onset of arthritis in a male over 6-years of age , acute anterior uveitis , or history of ankylosing spondylitis , enthesitis - related arthritis , sacroiliitis with inflammatory bowel disease , reiter 's syndrome or acute anterior uveitis in a first - degree relative undifferentiated arthritis : arthritis that fulfills criteria in no category or in two or more of the above categories . cacp syndrome can be clinically mistaken for polyarthritic jia or systemic jia with pericarditis . in cacp syndrome , children usually present with a joint swelling with absence of features of inflammation and examination reveals camptodactyly . jia is primarily an inflammatory arthritis with or without systemic involvement . on laboratory investigations , patients with jia have elevation of both esr and crp , since it is an inflammatory condition , while these parameters are normal in patients with cacp syndrome . radiologic features of cacp syndrome - related arthritis include those of a non - erosive arthropathy with large joint effusions . inter - osseous herniation of the joint capsule and fluid produces fluid - filled intra - osseous cysts with enhancement of the capsule . these cysts particularly are characteristic of cacp syndrome and are not seen in jia . in the acute phase of jia , imaging shows evidence of effusions and local hyperemia ( due to its inflammatory nature ) as initial widening of joint space , soft - tissue swelling , periarticular osteopenia , and enlargement of the epiphyses [ figure 5 ] . in the chronic stage , the inflammatory pannus causes destruction and leads to findings of joint erosions and joint space narrowing with eventual subluxation , dislocation and ankylosis leading to epiphyseal disturbances with resultant growth abnormalities and deformities . coronal stir image of both knees ( on 3 t system ) shows large effusions . small intraosseous cysts are identified along the medial femoral condyle ( arrows ) the acute non - erosive phase of jia may present with joint effusions and periarticular osteopenia [ figure 5 ] and hence lead to radiological confusion with cacp syndrome . however , in chronic cases of jia cartilage destruction , erosions , and ankylosis is seen . destruction of articular cartilage is also not seen in cacp , however , in advanced or long - standing disease , cartilage destruction may occur without erosive change . the synovial thickening seen in cacp is thin compared to the florid thickening and enhancement in jia . a recent in vitro study demonstrated that rehabilitative joint motion can stimulate chondrocyte prg4 secretion , suggesting that physical therapy may aid in the resolution of the camptodactyly and be appropriate as potential therapy for the arthritis involving the other joints . cacp syndrome is an autosomal recessive syndrome characterized bycamptodactyly , arthropathy , coxa vara and pericarditis with distinct radiological and histopathological features and should be considered in juvenile patients presenting with non - inflammatory arthropathy . increased awareness of this familial condition is required to prevent confusion with other inflammatory musculoskeletal conditions seen during childhood , particularly juvenile idiopathic arthritis . differentiation from jia is clinically important in view of the different management prototcol for the two conditions , and in particular , because of the possible severe side effects associated with treatment for jla .
camptodactyly - arthropathy - coxa vara - pericarditis ( cacp ) syndrome is an inherited disorder characterized by congenital or early - onset flexion camptodactyly , childhood - onset of non - inflammatory arthropathy , often associated with non - inflammatory pericarditis or pericardial effusion and progressive coxa vara . 
 the causative gene is located on chromosome band 1q25 - 31 . 
 this gene encodes for  proteoglycan-4  ( prg-4 ) , which is a surface lubricant for joints and tendons . 
 this syndrome has distinct radiological and histological features , which are important to recognize since it may clinically mimic juvenile idiopathic arthritis and mutation studies may not be easily available . 
 we describe a case of a 3-year 3-month - old female with features of cacp syndrome .