BACKGROUND Catatonia can occur in various neuropsychiatric disorders and is usually treated with benzodiazepines. So far, although 1 case of dementia with Lewy bodies (DLB) with catatonia has been reported, there have been no reports on patients with DLB whose initial symptom was a catatonia. Here, we present a patient who developed benzodiazepine-resistant catatonia and was subsequently diagnosed with DLB based on DLB biomarkers. CASE REPORT The patient was a 92-year-old woman who had not been diagnosed with dementia before. At the age of 91, she experienced catatonia and was initially treated with lorazepam, which did not improve her condition. Later, she transferred to our hospital and was treated with amantadine. Amantadine improved her catatonic symptoms; however, a decline in her cognitive function was observed. We therefore explored the cause of cognitive impairment through imaging studies. We found that the patient did not have the core clinical features of DLB (ie, visual hallucinations, parkinsonism, cognitive fluctuations, and rapid eye movement sleep behavior disorder) but had 2 indicative biomarkers on 123I-metaiodobenzylguanidine myocardial scintigraphy and dopamine transporter imaging. Possible DLB was diagnosed according to the diagnostic criteria. CONCLUSIONS Our case study suggests that catatonia can be an initial symptom of DLB. Moreover, considering the plausible pathophysiology of catatonia in DLB, amantadine treatment may be the most rational choice for the condition when benzodiazepine treatment is ineffective.