Purpose: Visual hallucinations can occur within the central nervous system and may be associated with a lesion anywhere in the visual pathway. The purpose of this study was to assess "ictal" regional cerebral blood flow with Tc-99m ethylcysteinate dimer (ECD) SPECT in patients having acute hallucinations, and to compare the findings to the "interictal" state.
Methods: A prospective study was performed to evaluate patients admitted to the neurology department with nonpsychiatric and nonepileptic visual hallucinations. The nine patients included in the study underwent thorough neurologic and psychiatric evaluations. A computed tomographic (CT) scan was performed when each patient was admitted, and electroencephalographic (EEG) recordings were made during their hallucinations. All patients underwent a brain SPECT while having acute hallucinations (ictal SPECT), and a follow-up scan was obtained 2 to 3 weeks later.
Results: All patients had normal ictal EEG findings during the hallucinations. Seven of nine patients had increased perfusion on the SPECT studies in one or more regions, with a mean lesion-to-contralateral ratio of 2.1 (range, 1.5 to 2.7). Three of the seven patients had findings consistent with a cerebrovascular accident. After treatment, the hallucinations disappeared in two patients and the motor deficit improved dramatically. The follow-up SPECT study showed significant improvement in all patients 1 week later. Charles Bonnet syndrome, frontal lobe dementia, and Anton syndrome were diagnosed in three other patients, and the last one had no identifiable background disease, all with normal findings of EEG, CT, and magnetic resonance examinations. They all responded readily to carbamazepine therapy, and the follow-up SPECT study showed resolution of the findings. Two of nine patients showed posterior cortical hypoperfusion, and eventually Lewy body disease was diagnosed. The SPECT showed no evidence of regional hyperperfusion.
Conclusions: This prospective preliminary study suggests that brain imaging using SPECT may be useful in identifying the mechanisms and evolution of blood flow abnormalities in certain subgroups of patients who have visual hallucinations and may assist in the selection of specific therapy.