Neuropathic pain is defined as pain that originates due to a lesion, dysfunction or disease, e.g. diabetes, human immunodeficiency virus infection, herpes zoster, chemotherapy or surgery, and which affects the peripheral or central nervous system. This results in abnormal neural function, often presenting in an individual as sensory pain-related symptoms which are either positive, i.e. hyperaesthesia or hyperalgesia; or negative, i.e. hypoaesthesia or anaesthesia. Patients often describe neuropathic pain as numbness or as a shooting, stabbing, burning, electric, tingling or "pins and needles" sensation. The quality of life of patients with neuropathic pain is often compromised as many have difficulty sleeping, lack energy, and experience drowsiness and altered concentration, and this can potentially progress to a stage in which the patient is physically and psychologically distressed.