BACKGROUND Dementia with Lewy bodies (DLB) is a common cause of dementia. Given the similarities between the symptoms of DLB and non-DLB Alzheimer disease (AD) and related dementias, patients can sometimes be misdiagnosed with AD. To increase the sensitivity of current DLB guidelines, the DLB Consortium published its fourth revised report in 2017 with increased diagnostic weight given to dopamine transporter (DAT) uptake in the basal ganglia, demonstrated by single-photon emission computed tomography or positron emission tomography imaging. We aimed to describe the role of DAT scans in evaluating dopamine deficiency in patients with overlapping symptoms of AD and DLB. CASE REPORT We present case studies of 3 patients with memory impairment who had a diagnosis of probable AD and were being treated with cholinesterase inhibitors. During treatment, dopamine deficiency was suspected and DAT scans were performed. All 3 patients revealed severe DAT deficits in the bilateral corpus striatum. These results were consistent with probable DLB as per the current revised DLB Consortium report. All patients received treatment with carbidopa/levodopa and demonstrated improved overall function. CONCLUSIONS All 3 of our cases demonstrated the role of DAT scans in evaluating dopamine deficiency syndromes in patients with overlapping symptoms of neurocognitive disorders. Thus, a DAT scan is critical for establishing an earlier and more definitive diagnosis of DLB, which provides treatment options for dopamine replacement. It also assists providers with prognostication of dopamine deficiency syndromes and is therefore beneficial in counseling patients and caregivers.