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)