Neuropathic pain is defined as pain in association with nerve injury or dysfunction.
It may be triggered by numerous insults including direct nerve injury, infection, metabolic dysfunction, autoimmune disease, neoplasm, drugs, and neurovascular disorders.
It may reflect the pathologic operation of a dysfunctional nervous system rather than a manifestation of any underlying pathology itself (i.e., phantom limb pain, complex regional pain syndrome). Patients may paradoxically experience pain and hypersensitivity in an area of denervation.
[...] Difficult to estimate precisely the incidence, prevalence, and sex differences given the number of disease-specific indications for neuropathic pain Prevalence Estimated at of population RISK FACTORS Diabetes mellitus Alcohol abuse Trauma Nutritional deficiencies (B12, folate) Medications (AIDS medications DDC and DDI, antibiotics metronidazole and isoniazid, some chemotherapeutics, amiodarone, hydralazine, phenytoin, nitrofurantoin) PATHOPHYSIOLOGY Not well understood. Multiple complex mechanisms likely involved in peripheral and central nervous system dysfunction ETIOLOGY Typically associated with a predisposing factor In addition to possible etiologies listed as "Risk Factors" above, others include - Demyelinating disorders (multiple sclerosis, Guillain-Barre) - Infections (HIV/AIDS, herpes zoster) - Neoplasm (primary or metastatic) - Neurovascular (central post stroke syndrome, trigeminal neuralgia) - Autoimmune disease (Sjogren syndrome, polyarteritis nodosa) - Structural disease (herniated disc disease) Neuropathic pain of the lower back represents over 1/2 of all those with neuropathic pain. [...]
[...] - Precautions: Small therapeutic-to-toxic window; use caution in prescribing to those with cardiac risk factors, glaucoma, urinary retention; suicide; absolute contraindication with MAOIs - Interactions: Numerous possible drug-drug interactions (type 1C antiarrhythmics, SSRIs, anticholinergics, sympathomimetics, CNS depressants) - Adverse effects: QT interval abnormalities, arrhythmias, sedation, dry mouth, constipation, sexual dysfunction, weight gain, postural hypotension Tramadol - Dosage: 250 mg/d in divided doses, max 400 mg/d - Precautions: Avoid in those with seizure history - Interactions: Increased seizure risk in those taking SSRIs, TCAs, MAOIs, neuroleptics concomitantly; increased risk of serotonergic symptoms if used with SSRIs, MAOIs; adjust dose for renal insufficiency, hepatic disease - Adverse effects: Dizziness, nausea, constipation, somnolence, orthostatic hypotension Lidocaine patch - FDA approved for treatment of postherpetic neuralgia but has been used for other focal neuropathic pain syndromes. [...]
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