Differential diagnosis: nociceptive and neuropathic pain.

Pain, both acute and chronic, affects millions of people in the United States. Pain can be categorized along a variety of dimensions, including one of the most important divisions, nociceptive versus neuropathic pain (NP). Nociceptive pain results from activity in neural pathways secondary to actual tissue damage or potentially tissue-damaging stimuli. NP is chronic pain that is initiated by nervous system lesions or dysfunction and can be maintained by a number of different mechanisms. Three common conditions that are often associated with acute and chronic NP are painful diabetic peripheral neuropathy (DPN), painful postherpetic neuralgia (PHN), and cancer. Although estimates of DPN vary widely depending on the assessment criteria employed, as many as 50% of people with diabetes have some degree of DPN. PHN develops secondary to herpes zoster infection, and there are 600,000 to 800,000 cases of herpes zoster in the United States each year, with 9% to 24% of patients progressing to PHN. Acute or chronic NP may occur in more than 50% of patients with cancer pain. Patients with painful DPN, PHN, or cancer may present with a variety of acute or chronic NP symptoms, and it is important to distinguish these conditions from other pain syndromes so that appropriate therapy can be initiated.