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Neurosurgical Procedure Review

Name of Procedure: Thermography.

Reason for Review: Revision of previous review of Thermography of 23 March 1982.

Description of Procedure:

  1. Infrared thermography. There are a variety of infrared scanning devices commercially available. Essentially the device converts radiated electromagnetic thermal energy into electronic video signals which are amplified and transmitted to a display monitor. As many as 64,000 discrete points are imaged and when the signal is on a cathode ray screen this corresponds to 64,000 different points of thermal monitoring with each point representing the temperature measurement encompassing a skin surface area of 1 mm' when the camera-to -- object distance is 50 cms. Increasingly, computerized thermographic systems are becoming available for data now and interpretation which enhance objectivity by quantifying the thermal data eliminating observer bias. Nevertheless, as with liquid crystal thermography discussed below it is critically important that the physician as well as the technician gathering and interpreting this data be well versed in the application of the technique as well as the interpretation as it is displayed.
  2. Liquid crystal thermography. Liquid crystal thermography uses flexible sheets in which cholesterol crystals are imbedded. On contact with the body surface the cholesterol crystals absorb heat and undergo structural changes concomitant color changes. These therefore are directly related to skin temperature and provide a means for mapping cutaneous thermal data. Even though liquid crystal thermography is significantly less expensive than infrared equipment its technique is time consuming and exacting requiring the highest level of training knowledge and experience on the part of the technician with ongoing supervision by the physician-thermologist. This system at the present time is difficult to computerize for quantification of the data and it is extremely susceptible to observer bias. Another drawback is that liquid crystal thermography requires firm and even contact and therefore the application is limited to flat parts of the body as it is difficult to achieve adequate and even contact with deeply concave parts of the body. The thermographic unit is used in a temperature compensated room kept at 20 degrees centigrade. The patient's back or the extremities to be examined are exposed and allowed to equilibrate with the temperature for 10-15 minutes.

Background: Skin temperature is a reflection of cutaneous blood flow under the control of the autonomic nerve system. A number of general and autonomic mechanisms have been proposed as the pathophysiological basis for skin temperature changes and neuromuscular disorders, Among the proposed general mechanisms are localized muscular activity, antidromic stimulation of sensory nerves, and the stimulation of the sinuvertebral nerves. Proposed mechanisms implicating the autonomic system involves stimulating the of the spinal parasympathetic nerves or the sympathetic vasodilator system, thermal alterations resulting from sympathetic vasoconstriction, and segmental regulation by somato -- sympathetic reflex. Ongoing research will lead to greater depths of understanding of the scientific basis for skin temperature changes. Suffice it to say that these skin temperature changes can be measured and the lack of a biochemical or physiologic mechanism to explain the scientific basis of established medical diagnostic to therapeutic procedures is not unique. Thermal homeostasis is maintained by feedback mechanisms which operate through a temperature regulating center in the hypothalamus. Heat sensitive neurons firing in response to an increase in the temperature of the blood flowing through the preoptic nucleus. The resulting inhibition of sympathetic neurons in the posterior hypothalamus reduces the normal vasoconstrictor tone of blood vessels in the extensive subcutaneous venous plexus causing vasodilation and concomitant heat loss. Conversely the flow to venous plexus blood is markedly reduced in response to constriction of sympathetically innervated arterial venous anastomosis in the subcutaneous plexus. Central control of skin temperature affects both sides of the body uniformly and simultaneously resulting in symmetry of thermal patterns. Abnormal thermograms occur in response to defective vasomotor mechanisms which cannot be demonstrated by conventional radiologic studies. Therefore, thermography is a test that images physiologic activity, not anatomic reality. Defective vasomotor mechanisms result in thermal asymmetry. While nerve injury initially results in a temperature increase in the area of distribution of nerves; in the later stages of the injury the area becomes colder.' The presence of a significant temperature difference between corresponding areas of opposite sides of the body is highly suggestive of nerve impairment, therefore, the patient serves as his own control.

Nerve root irritation is manifest by an ipsilateral temperature decrease in the corresponding dermatome. In peripheral nerve injuries, although an acute nerve injury results in a temperature increase in the area of nerve distribution, the area becomes colder during later stages of the injury. The area of thermal abnormality remains confined to the area of distribution of the injured nerve."'.

Available Proof of Efficacy: Evidence of prospective studies. Prospective studies have shown the excellent sensitivity and good correlation of thermography with other imaging methods. A high correlation of 84~k has been demonstrated in studies comparing thermography and CT scanning of patients with low back and sciatica.' Surgical treatment has also shown similar high rates of sensitivity.". A large study of 805 patients with upper and low back pain confirm good correlation between thermographic evaluation and myelography, CAT scanning and EMG.' THe two objective tests for documentation of sensory radiculopathy, thermography and somatosensory cortical evoked potentials, show equal sensitivity in the diagnosis of clinical lumbosacral radiculopathy.'

Safety: The procedure is totally non -- invasive and does not involve ionizing radiation. It is without patient risk.

Conclusion of Review: Thermography is a safe and effective means for evaluation of vasomotor instability due to irritation or injury or spinal roots, nerves or sympathetic fibers. It is to be considered an adjunctive test and not solely diagnostic except in cases of reflex sympathetic dystrophy. While one cannot extend the technique of thermography to indicate the central phenomena of perception of pain, it is useful in detecting associated vasomotor instability and complex pain states associated with arthritis, soft tissue injuries, low back disease or reflex sympathetic dystrophy and does provide objective data to identify dysfunction in roots that are irritated in the lumbar spine, peripheral nerves that are irritated and damage to the sympathetic nervous system.

Review Prepared By: Lyle Leibrock, M.D.

Special Consultant: Sumio Uematsu, M.D.

Approval: CHAIRMAN TASK AND TERMINOLOGY

Subcommittee: P.R. Schwetschenau, M.D. 3/1988

President, AANS: George T. Trudall, M.D. 5/14/88

President, CNS: C.B. Shields, M.D. 6/8/88

Bibliography

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  2. White, J.C., Sreet, I.E. Pain and the leurosurgean: i fart' year experience. Springfield, Illinois, Charles C. Thoaas, 1969, Pg. 87-98.
  3. Brelsford, K.L., Ueaatsn, S.: Theraographic Presentation of Cutaneous Eensory and Vasoaotor Activity in the Injured Peripheral Kerve. Richter, C.P., Woodruff, B.C.: lumbar Syapathetic Deraataaes in Man Deterained by the Electrical Skin Resistance Kethod. Jr. of Meuroghysiology 1945; 8: 323-338.
  4. Guttaan, K.4.: Topographical Studies of Disturbances of Sweat Secretion kfter Coaplete Lesions of Peripheral Kerves. Jr. Neural Psychiatry 194Q;
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  7. Perelaan, R.B., Wexler, C.E., Kpers, P.H. et al.: Liquid Crystal Theraagraphy of the Spine and Extrealties. Its Value in the Diagnosis of Spinal Root Syndroaes. Jr. Eearosare. 1982; 56: 386-395.
  8. Gillstraa, P. Theraography and Lar Back Pain and Sciatica. Lrch Ortha Iraua Burg, 1985; 104: 31-36.
  9. Hubbard, J.E.: Statistical Revier of Theraagraphy in a Eeurolagical Practice, Pain Evaluation. Postgraduate Medicine, 1986; special edition. Pcs 65-72.
  10. Pisher, l. Ria, k. Chang, C.: Correlation Between Theraographic Findings and Soaatosensary Cortical Evoked Potentials in Luabasacral Radiculopathles. Theraalogy. 1986; 2: 29-33.