Ingrowth of Nociceptive Receptors into Diseased Cervical Intervertebral Disc Is Associated with Discogenic Neck Pain

Objective. To investigate the distribution of nociceptive nerve fibers in the cervical intervertebral discs of patients with chronic neck pain and determine whether these nociceptive nerve fibers are related to discogenic neck pain. Methods. We collected 43 samples of cervical intervertebral discs from 34 patients with severe chronic neck pain (visual analog scale [VAS] >= 70 mm), 42 samples from 36 patients who suffered cervical spondylotic radiculopathy or myelopathy without neck pain or with mild neck pain (VAS <= 30 mm) and 32 samples from eight donators to investigate their innervation immunohistochemically using an antibody against neuropeptide substance P. Results. The immunohistochemical investigation revealed that substance P-positive nerve fibers were obviously increased in number and deeply ingrown into the inner anulus fibrosus and even into the nucleus pulposus in the degenerative cervical discs of patients with severe neck pain in comparison with the discs of patients with cervical spondylotic radiculopathy or myelopathy and normal control discs (P<0.01). Conclusions. The current study may indicate a key role of nociceptive nerve fibers in the pathogenesis of neck pain of cervical disc origin.