Visceral cancer pain: Mechanism

Mechanisms of pain in cancer include

1. Mechanical : caused by distension and contraction of hollow visceral structures such as bowel lumen or stretching of solid organ capsule e.g. hepatic capsule
2. Ischemic : caused by tumor infiltration or compression of visceral blood supply
3. Inflammatory : inflammatory mediators released due to tumor infiltration – PGE2, serotonin
4. Neuropathic : tumor invasion of nerves supplying the viscera

Patients with visceral cancers may have pain as a consequence of therapy.

1. Persistent postoperative pain – post thoracotomy pain, post mastectomy pain
2. Radiation therapy related pain – radionecrosis, fibrosis, brachial plexopathy, chronic esophagitis
3. Chemotherapy related pain – peripheral neuropathy, bone pain, headache

Visceral pain is diffuse in nature and is referred to superficial structures due to convergence of visceral and somatic afferents on same neurons in dorsal horn of spinal cord. Activation of afferents from cell bodies in the dorsal horn cause expression of oncogene C-fos in laminae I, V , VII and X of dorsal horn in thoracolumbar spine. Both ventrolateral and dorsal column polysynaptic neurons have a role in nociception. Ascending tracts synapse in lateral thalamus followed by limbic centers and finally somatosensory cortex.