THE VALUE OF QUANTITATIVE GA-67 SINGLE-PHOTON EMISSION TOMOGRAPHY IN THE CLINICAL MANAGEMENT OF MALIGNANT EXTERNAL OTITIS

Malignant external otitis (MEO) is a severe infectious disorder usuall y caused by Pseudomonas aeruginosa, which most frequently affects diab etic patients. Due to its rarity, the diagnosis of MEO is often not ma de promptly, Extension into deeper structures or chronic osteomyelitis may occur without signs of infection on local clinical examination. O f the imaging techniques, magnetic resonance imaging provides a fairly adequate picture of the spread of the disease, but, as with computed tomography (CT) scanning and bone scintigraphy, the images remain unch anged for a long time after disease regression. The objective of this study was to establish whether quantitative gallium-67 single-photon e mission tomography (SPET) represents an accurate method for the assess ment of infection and, moreover, for the monitoring of therapeutic eff ect. Eight patients (five males, three females) with the clinical diag nosis of MEO were studied. In three patients antibiotic treatment was prolonged for several weeks because visual analysis of gallium scintig raphy still showed slightly increased uptake in the affected area on t he first follow-up scan. In one patient, it was decided to stop antibi otic treatment despite a slight increase in uptake on the second follo w-up scan. Lesion to non-lesion (L/NL) ratios obtained from Ga-67 SPET images at initial diagnosis and during follow-up were assessed in cor relation with clinical and biochemical data and with the results of CT scans. In addition to a raised erythrocyte sedimentation rate (ESR), all patients showed increased uptake on the affected side, with L/NL r atios ranging from 1.4 to 3.6 at the time of diagnosis. CT scans faile d to demonstrate abnormalities in four patients. Including four scans demonstrating slightly increased uptake in the affected area, L/NL rat ios after 6-8 weeks of antibiotic treatment were 1.0+/-0.1, Despite a persistently elevated ESR in the majority of patients, none of them de monstrated local recurrence or complications during follow-up. In all patients, leucocyte count was within the normal range throughout the c ourse, No relation was found between the slightly increased uptake on the follow-up scans and surgical treatment, It is concluded that in ad dition to the visual analysis of Ga-67 SPET imaging, L/NL ratios shoul d be calculated for-a more accurate assessment of disease activity in MEG. Despite visually slightly increased uptake, L/NL ratios of 1.0+/- 0.1 during follow-up are highly indicative of complete recovery, regar dless of ESR values or leucocytosis. CT scans are of little value for diagnosis or for monitoring of therapeutic effect.