Neuropathic Pain

What is neuropathic pain?

Neuropathic pain is “pain caused by a lesion or disease of the somatosensory nervous system.” A lesion refers to an abnormality that is evidenced by diagnostic tests (e.g., imaging, neurophysiologic studies, biopsies) or a known trauma to the nervous system. The term “disease” refers to lesions from a known underlying cause such as diabetes mellitus, stroke, vasculitis, and so on. Neuropathic pain can be due to aberrant somatosensory processing in either the peripheral or central nervous system (CNS). Of note, neuropathic pain is a clinical descriptor and not a diagnosis. 

Neuropathy is a disturbance of function of pathologic change in a nerve. If it is present in one nerve, it is called “mononeuropathy.” If neuropathy is present in several nerves, it is called “mononeuropathy multiplex,” whereas if it is diffuse and bilateral, it is often called “polyneuropathy.” Neuritis is a special case of neuropathy when nerves are affected by inflammation. Neuralgia is used to refer to any pain in the distribution of a nerve or nerves. 

Pain has been defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Neuropathic pain is defined as “pain arising as a direct consequence of a lesion or disease of the somatosensory system.” Thus neuropathic pain can be thought of as an unpleasant sensory and emotional experience associated with damage to innervated tissues but due to dysfunction of the peripheral or central nervous system. Descriptors (burning, stabbing) will often indicate tissue damage when in fact there is none.

How common is neuropathic pain, and who gets it?

Epidemiologic studies estimate a prevalence of 7% to 9.8% of the adult population may experience neuropathic pain, and up to 20% of patients with chronic pain may have neuropathic components.

How does neuropathic pain affect quality of life?

Neuropathic pain impacts mood, sleep, function, and overall health. The higher a patient rates their neuropathic pain on a scale of 0 to 10, the higher the negative impact of the pain on all of these domains. Negative mood associated with neuropathic pain includes both anxiety and depression. Similarly, higher pain scores are associated with more direct and indirect medical expenditures and more use of medications.

What are the conditions that sound similar to neuropathic pain

Fibromyalgia is a pain disorder characterized by widespread musculoskeletal pain and heightened pain response to pressure, often accompanied by fatigue, mood, and cognitive disturbance. Although patients may describe some symptoms including numbness, tingling, and paresthesia-like sensations, technically the International Association for the Study of Pain criteria for neuropathic pain is not met, as there is no demonstrable disease state or demonstrable lesion. Similarly, patients with complex regional pain syndrome (CRPS) type 1 may complain of neuropathic-like symptoms, including burning pain or allodynia, but there is no lesion, as opposed to CRPS type 2, which does include a component of specific nerve injury. Still many do not consider CRPS type 2 an entirely neuropathic syndrome.

What are common descriptors of the pain that a patient might give you when describing their possible neuropathic pain?

Patients may describe their pain as burning, tingling, electric-like, or shooting, and often report that the pain is unfamiliar or unlike typical pain experienced before. Many terms used to describe neuropathic pain are consistent with a dysesthesia, which is defined as an abnormal pain complaint. Patients may also describe unpleasant numbness or a painful itch sensation.

What history may a patient with neuropathic pain report?

People with neuropathic pain may report a history of disease, toxin exposure, or injury that can cause nerve damage and therefore neuropathic pain. Examples include a history of diabetes (possible diabetic peripheral neuropathy [DPN]), human immunodeficiency virus (HIV) infection with treatment (HIV associated neuropathy), treatment with chemotherapy, orthopedic or spine surgery with persistent pain after the surgery, or other injury associated with loss of motor or sensory function. Additionally, patients with neuropathic pain may already have a history of another neuropathic pain problem.

What are common physical exam findings in patients with neuropathic pain?

Exam may reveal allodynia (pain created by a normally nonpainful stimulus such as a light brush or touch), hypoalgesia or hyperalgesia (relatively decreased or increased perception of a noxious stimulus, respectively), hypoesthesia or hyperesthesia (relatively decreased or increased perception of a non-noxious stimulus, respectively), or hyperpathia (exaggerated pain response). There may be focal neurologic deficits including weakness, reflex changes, or motor weakness. In an extremity there may be autonomic changes such as swelling and vasomotor instability (observed as color changes, livedo reticularis, and temperature changes). Trophic changes may also be seen including alterations of the skin, subcutaneous tissues, hair, or nails.

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