DECREASED CEREBRAL GLUCOSE-METABOLISM IN PATIENTS WITH BRAIN-TUMORS -AN EFFECT OF CORTICOSTEROIDS

The authors measured cerebral glucose metabolism (CMR(glc)) using [F-1 8]fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) in pa tients with brain tumors to evaluate the effect of exogenous corticost eroids (in this instance, dexamethasone) on glucose metabolism. Fifty- six FDG-PET studies obtained in 45 patients with unilateral supratento rial brain tumors were analyzed. Patients with brain tumors were divid ed into three groups: 1) patients with cushingoid symptoms, who had be en treated with combinations of radiotherapy and chemotherapy taking o ral dexamethasone; 2) patients not taking dexamethasone but treated wi th radiotherapy; and 3) patients not taking dexamethasone who had not been treated with radiotherapy. Serial FDG-PET scans were obtained in eight of the cushingoid patients. Glucose metabolism was measured in t he contralateral cerebral and ipsilateral cerebellar hemispheres in pa tients and compared to measurements taken from 19 normal volunteers. T he authors found that in the cushingoid brain tumor patients there was a marked reduction in CMR(glc) compared to normal volunteers and othe r brain tumor patients (Kruskal-Wallis test; p 0.001). In the majority of patients who had serial FDG-PET scans, there was a decline in gluc ose metabolism over time and in one patient, in whom dexamethasone was reduced in dosage, there was a subsequent increase in CMR The authors conclude that there is a generalized reduction in CMR in brain tumor patients taking dexamethasone compared to other brain tumor patients a nd normal volunteers, and that this effect is independent of radiother apy, concurrent anticonvulsant medication: acid transhemispheric funct ional disconnection (transhemispheric diaschisis).