Usefulness of ^99mTc-HMPAO leukocyte scintigraphy in necrotizing external otitis/skull base osteomyelitis

Necrotizing external otitis (NEO) is a rare but serious disease of the skull base (osteomyelitis). Immunosuppressed, and elderly patients are most commonly affected. The most common pathogen is Pseudomonas aeruginosa. Early diagnosis is crucial for the prognosis. To establish the diagnosis, both positive imaging findings, and clinical criteria are required to be met. Imaging is used during follow-up to monitor a potential recurrence due to its high risk, even after successful treatment. The use of radiological or nuclear medicine methods (scintigraphy) in the management of NEO is not currently standardised. We report a series of 5 patients with necrotizing external otitis/otogenic skull base osteomyelitis over a period of 12 years (2012-2024). In all patients, ^99mTc-HMPAO (hexa-methyl-propylene-amine-oxime) labelled autologous leukocyte scintigraphy was used to diagnose, to monitor therapy response and for a follow-up. The primary diagnosis of necrotizing otitis was confirmed by scintigraphy in all cases (positive predictive value of 100%). In monitoring of treatment response, true negative scintigraphic findings were observed in two cases, two findings were false-negative (negative predictive value of 50%), and one case was found to be a false-positive. In a follow-up, the recurrence of the disease was truly detected or ruled out by subsequent scintigraphy in all subjects. Technetium-99m-labelled leukocyte scintigraphy is a convenient and reliable method, especially for diagnosing, and follow-up of necrotizing external otitis/otogenic skull base osteomyelitis. In terms of monitoring treatment response, further studies could be suggested for improving the estimated low negative predictive value.