CACP Syndrome: A Rare Non-inflammatory Arthropathy Often Misdiagnosed as Juvenile Idiopathic Arthritis – Clinical Insights and Diagnostic Approach

CACP (Camptodactyly-arthropathy-coxa-vera- pericarditis) is rare autosomal recessive genetic condition characterized by progressive joint involvement at an early age. The prevalence of this condition remains unknown. It occurs due to defect in the gene PRG-4 (Proteoglycan-4) on chromosome 1q encoding for protein lubricin. Camptodactyly is non-traumatic flexion deformity of proximal interphalangeal joints (PIPs). It is commonly seen involving little finger as a sporadic condition. In CACP, it is usually congenital or early childhood onset and involves both the hands.Arthropathy is non-inflammatory and tend to involve large joint with mirror image symmetry. It is unresponsive to DMARDs. (disease modifying anti-rheumatic drugs) Children with CACP present to rheumatology clinics with joint swellings and frequently misdiagnosed with JIA (Juvenile idiopathic arthritis) as it is the most prevalent cause of joint swellings in children. However, diagnosis of JIA is clinical and there is lack of clear diagnostic markers, which causes further confusion.Absence of other inflammatory signs, mirror image symmetry of joint involvement and partial response to treatment for JIA may be the clues to reinvestigate for genetic causes in such cases. X-rays findings may be helpful in differentiating the two as well.