Minor hallucinations (MH) are commonly observed in Parkinson disease (PD) and are increasingly recognized as important markers of cognitive decline. ^{Reference Lenka, Pagonabarraga, Pal, Bejr-Kasem and Kulisvesky1–Reference Bejr-Kasem, Sampedro, Marin-Lahoz, Martinez-Horta, Pagonabarraga and Kulisevsky2} Metamorphopsia, a rare visual illusion phenotype, is infrequently reported in PD. ^{Reference Sasaki, Yokoi and Takahashi3} We report on a patient with PD who experienced metamorphopsia as part of an evolving cognitive profile, which preceded precipitous cognitive decline and progression of visual phenomena with loss of insight.

A male of European ancestry developed right-hand resting tremor at age 66. By age 68, he reported micrographia, hypophonia, and difficulty lifting his right leg while ambulating. Eight years prior to motor onset (age 58), he developed anosmia and dream re-enactment behaviors. Neurological examination at age 68 revealed resting tremor, bradykinesia, and rigidity, most pronounced on the right. His mini-mental state examination (MMSE) score was 30/30. The patient was 6’1” tall and weighed 182 lbs. He was diagnosed with PD but initially declined medications for treatment of motor symptoms. One year later, at age 69, he was started on oral levodopa (LD) with excellent results. Two years after initiating medication and titrating to a LD equivalent daily dose of 800 mg, he developed motor fluctuations and peak-dose dyskinesia. At age 72, his MMSE score was 29/30, and he now described “brain fog” during wearing off of LD. He denied any form of visual phenomena or other hallucinations at this time.

At age 73, he began experiencing features of metamorphopsia. This occurred in the absence of increasing levels of dopaminergic medications. He often perceived the staff members at his retirement community as “giants” despite them being much shorter in stature compared to himself. He estimated the height of these giants at 15–20 feet tall. Occasionally, he perceived rooms as being larger to accommodate these giants, causing him to feel small. During the first few weeks of experiencing these illusions, he frequently asked them to stand back-to-back with him to compare heights. After several encounters, he recognized that his perception of them as giants was distorted and thereafter maintained good insight into the phenomenon. Presence hallucinations emerged within 6 months, and repeat examination revealed polyminimyoclonus.

At age 74, his metamorphopsia resolved, but passage hallucinations developed alongside cognitive decline, with his MMSE score dropping to 21/30. He was previously adept with computers but had lost the ability to use this technology, except for playing simple games. His family also discovered that he was attempting to send emails from Microsoft Word. Within six months, he developed structured hallucinations (SH). These involved visual, auditory, and tactile hallucinations. He described a group of six people entering his home and making themselves comfortable by sitting in his favorite chair or eating his meals. He often became upset during these episodes, calling the police and attempting to physically remove the figures from his home. Despite numerous attempts by family and healthcare workers to explain the nature of these phenomena to him, efforts were futile as he no longer maintained insight. He was investigated for delirium twice within three months, but no medical etiology was identified for his rapid neurocognitive decline. Brain imaging with a CT scan was unremarkable. His symptoms of psychosis were refractory to quetiapine 50 mg PO BID. He was subsequently started on rivastigmine 3 mg PO BID, which led to improvement of his hallucinations after 4 weeks of therapy. His cognitive function was otherwise unchanged.

This case highlights the evolving nature of visual phenomena in PD, with a focus on metamorphopsia and its progression to SH with cognitive decline. Our patient’s rate of decline was striking. Currently, there is limited evidence on the rate of minor hallucinations progressing to SH, but a 2016 study found that 28.5% of patients with MH had made this transition within 4.4 years. ^{Reference Pagonabarraga, Martinez-Horta and Fernández de Bobadilla4} We are not aware of any studies reporting the rate of progression to SH and dementia in PD patients from the onset of MH.

Our patient’s abrupt cognitive decline within a year of developing metamorphopsia aligns with observations that minor visual phenomena may predict worsening cognitive function and progression to psychosis. ^{Reference Lenka, Pagonabarraga, Pal, Bejr-Kasem and Kulisvesky1–Reference Bejr-Kasem, Sampedro, Marin-Lahoz, Martinez-Horta, Pagonabarraga and Kulisevsky2} This observation has led to proposals that MH may be used as a biomarker in PD. ^{Reference Pagonabarraga, Bejr-Kasem, Martinez-Horta and Kulisevsky5} It is unclear if different types of MH (passage, presence, or visual illusions) carry a higher risk of progressing to SH with cognitive decline.

Multiple brain networks and their connectivity have been studied in relation to psychosis in PD. ^{Reference Lenka, Pagonabarraga, Pal, Bejr-Kasem and Kulisvesky1} In 2011, Shine et al proposed the “attentional network dysfunction” hypothesis. This hypothesis describes a failure of recruitment through the dorsal attention network, which is responsible for sustained attention during ambiguous visual input, leading to incorporation of perceptual errors into the visual processing stream. ^{Reference Shine, Halliday, Naismith and Lewis6} Unfortunately, longitudinal studies focusing on the dynamic transition between functional connectivity in different types of hallucinations are lacking. We are aware of a single study that attempted to measure the impact of early treatment of MH using rivastigmine. ^{Reference van Mierlo, Foncke and Post7} The trial was prematurely discontinued due to a lack of funding and difficulty with patient enrollment. Another limitation was that participants in the study had a mean MH onset of 2.2 years (standard deviation 2.8 years) prior to enrollment.

Given the recent observations that both prevalence and incidence of PD are increasing, ^{Reference Noyes, Rajput, Kim and Rajput8} further research is warranted to investigate if early intervention through a variety of treatments can modify brain connectomics. The goal is to produce a disease-modifying effect through preservation of normal functional connectivity. Additionally, further exploration of the prognosis surrounding different types of MH may help the rising tide of individuals with PD better prepare for the years ahead.

Metamorphopsia is a rare phenomenon in PD. Our case highlights a patient with precipitous cognitive decline progressing to psychosis after the onset of metamorphopsia. There is a lack of published data describing the rate of MH progressing to SH and dementia in patients with PD. Identifying this rate of progression may help predict prognosis and guide treatment in PD patients who develop MH. Furthermore, narrative descriptions of MH phenotypes may provide additional insights into prognosis and thus should be explored.