Nociceptive role of substance-P in the knee joint of a patient with congenital insensitivity to pain.

This case report describes the immunocytochemical examination of tissue from a 9-year-old black child diagnosed with congenital insensitivity to pain at age 5. A recent fall and resulting patella fracture required surgical treatment. Biopsies of the distal pole and surrounding soft tissue, as well as a sample of his patellofemoral joint fluid, were taken at the time of partial patellectomy and analyzed for substance-P (SP). Morphologic staining of the patella showed a grossly degenerated patellofemoral articular surface. Examination of tissue sections stained either immunocytochemically with diaminobenzidine DAB or by a rhodamine fluorescent labeling technique showed no evidence of SP-positive nerve fibers. Furthermore, only a trace amount of SP (7.29 pg/ml) was detected in a sample of the patient's knee joint synovial fluid. This patient's absence of pain sensation in conjunction with the absence of SP nerve fibers in stained patella sections and identification of only trace levels of SP in his synovial fluid, further implicates this neuropeptide in nociceptive innervation of diarthrodial joints.