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Background There are numerous disorders of the peripheral and central nervous system that lead to chronic pain states (see below). The pathophysiology of nerve injury in chronic pain can be highly complex and can therefore lead to unpredictable response to treatment courses. Patient history, physical and various standard tools have historically been used to evaluate the nociceptive system, often lacking sensivity and with inherent examiner bias. Imaging tools represent the most commonly used diagnostic tools, although these represent a picture of anatomy, not a measure of nerve function and can be associated with a significant number of false-positives. EMG and nerve conduction testing do not evaluate small-caliber, pain-mediating C and A-delta fibers. Quantitative Sensory Testing (QST) Quantitative Sensory Testing (QST) enables the user to evaluate specific components of the nociceptive system, including pain-mediating unmyelinated C-fibers that can be extremely useful to the practicing pain physician. The TSA-II NeuroSensory Analyzer allows investigation of the coexistence of pain with both central and peripheral nervous system abnormalities, to include permitting diagnosis of neuropathic pain syndromes. "In the clinical setting, quantitative sensory testing is becoming a clinical standard for evaluation of certain chronic pain conditions" (Stojanovic et al; Current Review of Pain, 1998). Nerve Fibers Nerves consist of fibers of variable diameter with the thicker fibers having a faster conduction velocity. Three types of fibers are generally recognized in the sensory subclass of nerve fibers, with small-caliber, pain-mediating fibers representing roughly 70% of the peripheral nerve system:
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