Discussion:
We provide findings on two uncommon illusions seen in individuals diagnosed with DLB.
The first patient reported experiencing a phenomenon known as the room tilt illusion, characterized by the perception of items flowing downwards towards the floor and a distorted sense of the surrounding environment being skewed to one side. (7)
Room tilt illusion occurs when there is a mismatch between the visual and vestibular inputs that reach the visuospatial cortex. The vestibular afferents may be disrupted due to the defect in the sensory inputs (from the peripheral nervous system or spinal cord) (8), brainstem, or cerebellar lesions. (9) When evaluating patients with Room Tilt Illusion, we can categorize them as having a direct pathology in the vestibular system and its sensory afferents or in connection with the cortex. (3) In our patient, The episodic pattern of the illusion was against subjective visual vertical tilt, in which the constant environment vertical torsion is the result of otolithic dysfunction. (10) We excluded infratentorial structural abnormalities and epileptic episodes by Brain MRI and EEG, respectively. The absence of vertigo, tinnitus, and hearing loss was against a previous vestibular pathology. To our knowledge, our case is the first reported Room Tilt Illusion in DLB. It has been reported previously in a case of Parkinson’s disease and Multiple system atrophy. (3, 11) In 2009, the brain single photon emission computed tomography (SPECT) of a Parkinson-affected patient with Room tilt illusion revealed hypoperfusion in bilateral occipital cortices and the posterior part of the right intraparietal sulcus. This finding became a helpful imaging biomarker of DLB in 2024.(11, 12)
We suggest that the Room tilt illusion in DLB is the result of cortical disintegration. Therefore, it is plausible to indicate that the presence of visuospatial dysfunction early in the disease course of patients with Parkinsonism may be a diagnostic clue to the DLB.
Our second patient’s primary complaint was palinopsia, a visual disorder characterized by the persistence of afterimages even after the removal of visual stimuli. Palinopsia is classified into two kinds based on its content (hallucinatory and illusionary) and the time gap between the original picture and its afterimage (immediate and delayed forms, occurring within a few minutes or hours). (13) A distinct and detailed afterimage with a high level of clarity characterizes hallucinatory palinopsia. (14) Our patient had delayed hallucinating palinopsia.
Palinopsia may occur in people with brain lesions, mainly in the Post-geniculate cortex, medications (Topiramate), seizures, psychiatric illness (schizophrenia), and migraine. (15, 16) A 2015 case report discussed a case of palinopsia due to unilateral vestibular deafferentation after a large cholesteatoma surgery. The authors explained that palinopsia occurs when the vestibular input delays mismatches of visual inputs reaching the cortex. (17) Our brain MRI findings showed no evidence of structural abnormalities. There was no record of any previous head injury. The EEG revealed no epileptic activity. The patient’s medication record did not indicate the likelihood of drug-induced palinopsia. Ultimately, the patient’s symptoms did not satisfy the criteria for any significant mental condition.
Research has shown that DLB is distinguished by a consistent decrease in metabolic activity in the parieto-occipital area, as seen in Brain SPECT. (5) There is a correlation between decreased blood flow on both sides of the occipitotemporal cortex, more intense hallucinations, and worse visual processing. (18) In a study conducted in 2024, palinopsia was categorized as a minor visual hallucination that occurred when a partial defect in white matter connected dorsal and ventral attention networks and visual areas.(19)
In addition to the role of occipitotemporal hypoperfusion, we propose that early aggregation of Alpha Synucleins in the vestibular nucleus of the brainstem may explain the vestibular-visual mismatch and associated illusions along with early recurrent falls in the early phase of DLB. (6, 20)