Malignant external otitis (MEO) is a potentially fatal otitis occurring in diabetic and immunosuppressed patients, which may cause cranial nerve palsies and massive thrombophlebitis of the brain. We studied five diabetic patients with the clinical diagnosis of external otitis who were suspected of having MEO and one diabetic patient presumed cured from MEO. All of them underwent methylene diphosphonate, nanocolloid and gallium single-photon emission tomography studies with quantitative analysis on the basis of regions of interest and count profile curves. This combined assessment helped us to diagnose and follow-up soft tissue and temporal bone infection, especially in the case of transsphenoidal extension of the disease, since conventional radiology and computed tomography were of no particular help. On the basis of these results, we consider scintigraphic demonstration of skull base infection as a fourth criterion of MEO given that the classical Chandler's triad (diabetes, granuloma, and Pseudomonas aeruginosa) is not always present.