Arthritis in a child secondary to congenital insensitivity to pain and self-aggression. Why and when pain is good?

A 9 year-old female child presented with recurrent arthritis of ankles, left knee and unequal leg length. Clinical examination revealed mild valgus deformity in her left knee with grade 2 effusion, arthritis of both ankles and deformity in her left wrist. Examination of the affected joints showed no evidence of tenderness upon active or passive movements and the patient did not show any limping upon gait analysis. Past history of the patient revealed evidence of previous dislocation of her left hip and previous fibular fracture. Revision of her previous x-rays showed left hip dislocation, fracture left fibula and fracture of right metatarsal bone after repetitive trauma which pass unnoticed. Recent x-ray of her left knee showed osteochondral injury. Laboratory investigations were done to rule out common causes of childhood arthritis and revealed: ESR 12 1st hours, CRP negative, negative rheumatoid factor, and negative ANA. Neurological evaluation of the patient documented congenital insensitivity to pain and EMG studies confirmed evidence of sensory neuropathy. Traumatic arthritis resulting from congenital insensitivity to pain with self-aggression is rarely encountered in children but should be considered in the differential diagnosis specially if radiological features point to repetitive trauma with attempts of healing.