Hallucinations in the Differential Diagnosis of Parkinsonism

Introduction

Parkinsonism is a clinical syndrome defined by the presence of bradykinesia with tremor, extrapyramidal rigidity, and postural instability. Progressive neurodegenerative parkinsonism is most commonly associated with idiopathic Parkinson's disease (PD), but is also a clinical feature in progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and vascular parkinsonism among other nosological entities. Over the past two decades, operational diagnostic criteria have been developed for these conditions, which appears to have improved diagnostic accuracy. Even so, it is common for patients to partially satisfy several different diagnostic criteria forcing clinicians to consider other factors outside these criteria when reaching a clinical diagnosis. In specialist movement disorder clinics, the clinical diagnosis may be incorrect in up to 15% of patients when compared to pathological diagnosis postmortem. This inaccuracy is even more apparent early in disease when clinical signs have yet to fully evolve and parkinsonian features are mild. Accurate diagnosis is important for informing the patient about their disease and prognosis, planning treatment strategies, and, in the future, for testing possible neuroprotective treatments.

Abstract

Visual hallucinations (VH) occur commonly in Parkinson's disease (PD) and dementia with Lewy bodies (DLB), but are reported much less frequently in other neurodegenerative causes of parkinsonism, such as progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration. This clinical sign may be helpful when considering the differential diagnosis of patients with parkinsonism. The observation that VH may be specific to Lewy body pathology probably reflects a greater vulnerability of the visual systems to PD and DLB neurodegeneration compared to other diseases. Topographic differences in pathology are probably the major factor producing VH in Lewy body diseases, rather than neurophysiological changes that are specific to α-synuclein protein accumulation. VH correlate with pathology in the limbic system and more specifically the amygdala that is frequently affected in PD and DLB but relatively preserved in other forms of parkinsonism often misdiagnosed as PD. In this review, we compare the published frequencies of VH in these different conditions to put into context the notion of VH as a clinical clue to underlying Lewy body pathology.

Keywords

hallucination, parkinsonism, Parkinson's disease, diagnosis, amygdala