EFFECT OF HYPERTHERMIA ON THE CENTRAL-NERVOUS-SYSTEM - A REVIEW

Experimental data show that nervous tissue is sensitive to heat. Anima l data indicate that the maximum tolerated heat dose after local hyper thermia of the central nervous system (CNS) lies in the range of 40-60 min at 42-42.5-degrees-C or 10-30 min at 43-degrees-C. No conclusions concerning the heat sensitivity of nervous tissue can be derived from clinical studies using localized hyperthermia. The choice whether or not to exceed the critical heat dose, as derived from laboratory studi es, in clinical practice is very much dependent on the clinical situat ion such as the anatomical site and volume of the tissue involved, and prior therapy. Data on clinical application of whole body hyperthermi a (WBH) show that nervous tissue can withstand a slightly higher heat dose than after localized heating, which might be the result of develo ping thermal resistance during treatment. Expression of thermotoleranc e was observed in the spinal cord of laboratory animals. After WBH in man at a maximum between 40 and 43-degrees-C for 6 h-30 min CNS compli cations were reported, but other complications seemed to be more life- threatening. Most studies indicate that impairment of the CNS after WB H was not due to direct heat injury to the brain or spinal cord, but w as secondary as a result of physiological changes. Heat, at least if a pplied shortly after X-rays. enhances the response of nervous tissue t o radiation. Neurotoxicity of chemotherapeutic drugs does not seem to be a limiting complication in hyperthermia if combined with chemothera py, but only few data are available. The limited clinical experience s hows that safe hyperthermic treatment of CNS malignancies or tumours l ocated close to the CNS seems feasible under appropriate technical con ditions with adequate thermometry and taking the sensitivity of the su rrounding normal nervous tissue into account.