Undetectable specific striatal [¹²³I]-ioflupane binding in patients with parkinsonism

[(123)I]-Ioflupane single photon emission computed tomography (SPECT) is widely used to evaluate the impairment of the nigrostriatal pathway in patients with parkinsonism. We describe a patient with visually undetectable specific striatal [123I]-ioflupane binding in the striatum. Of the 950 [123I]-ioflupane SPECT scans of patients acquired in our department, only one did not show any visually detectable striatal binding. To investigate this issue, we described multimodality imaging in this patient, including a second [123I]-ioflupane SPECT with a higher dose of [123I]-ioflupane, a [18F]-fluoro-l-dopa positron emission tomography (PET), a new MRI and an FDG-PET. Clinical and imaging data (FDG-PET and MRI) led to a diagnosis of progressive supranuclear palsy (PSP). Visual analysis of the second [(123)I]-ioflupane SPECT performed with a higher dose of [(123)I]-ioflupane confirmed nearly undetectable specific striatal binding of the tracer. The [(18)F]-fluoro-l-dopa-PET striatal binding was decreased. After ruling out all technical issues, an undetectable specific [(123)I]-ioflupane striatal binding in a patient with parkinsonism can be a sign of severe DaT loss as we have observed in a case of probable PSP even with moderate motor signs.