Eye of the tiger-like MRI in parkinsonian variant of multiple system atrophy

Imaging in Movement Disorders

OBJECTIVE

This article reviews commonly used imaging modalities in movement disorders, particularly parkinsonism. The review includes the diagnostic utility, role in differential diagnosis, reflection of pathophysiology, and limitations of neuroimaging in the setting of movement disorders. It also introduces promising new imaging modalities and describes the current status of research.

LATEST DEVELOPMENTS

Iron-sensitive MRI sequences and neuromelanin-sensitive MRI can be used to directly assess the integrity of nigral dopaminergic neurons and thus may reflect disease pathology and progression throughout the full range of severity in Parkinson disease (PD). The striatal uptake of presynaptic radiotracers in their terminal axons as currently assessed using clinically approved positron emission tomography (PET) or single-photon emission computed tomography (SPECT) imaging correlates with nigral pathology and disease severity only in early PD. Cholinergic PET, using radiotracers that target the presynaptic vesicular acetylcholine transporter, constitutes a substantial advance and may provide crucial insights into the pathophysiology of clinical symptoms such as dementia, freezing, and falls.

ESSENTIAL POINTS

In the absence of valid, direct, objective biomarkers of intracellular misfolded α-synuclein, PD remains a clinical diagnosis. The clinical utility of PET- or SPECT-based striatal measures is currently limited given their lack of specificity and inability to reflect nigral pathology in moderate to severe PD. These scans may be more sensitive than clinical examination to detect nigrostriatal deficiency that occurs in multiple parkinsonian syndromes and may still be recommended for clinical use in the future to identify prodromal PD if and when disease-modifying treatments become available. Multimodal imaging to evaluate underlying nigral pathology and its functional consequences may hold the key to future advances.

Eye-of-the-Tiger Sign with an Unexpected Pathological Diagnosis

Background

Clinical diagnosis of atypical parkinsonisms may be challenging. The eye-of-the-tiger sign on brain MRI, typical of neurodegeneration with brain iron accumulation, has been anecdotally observed in cases clinically diagnosed as atypical parkinsonisms.

Objectives

To show how clinical syndromes and even neuroimaging sometimes may lead the neurologist to a misunderstanding, just as to emphasize the important role of pathology to establish the final diagnosis in these cases.

Methods

Clinico-pathological case.

Results

A 67-year-old-woman presented with progressive painful stiffness and allodynia in her left arm. On examination, she presented parkinsonism without tremor with greater involvement of left limbs. She developed dystonia, with myoclonic tremor and hypoesthesia involving her left arm, as well as an impairment of balance with falls, a significant axial involvement with disabling rigidity, supranuclear gaze abnormalities, facial dystonia, dysphonia, severe dysphagia, and anarthria. There was no response to levodopa. Syndromic diagnosis and findings on neuroimaging are discussed. Afterwards, the underlying pathology is revealed.

Conclusions

We present the first case of neuropathologically confirmed multiple system atrophy with the eye-of-the-tiger sign on brain MRI. The presence of supranuclear vertical gaze palsy further complicated a correct clinical diagnosis. A pathological postmortem study remains essential to establish a definite diagnosis in atypical parkinsonisms.

Brain MRI Pattern Recognition in Neurodegeneration With Brain Iron Accumulation

Most neurodegeneration with brain iron accumulation (NBIA) disorders can be distinguished by identifying characteristic changes on magnetic resonance imaging (MRI) in combination with clinical findings. However, a significant number of patients with an NBIA disorder confirmed by genetic testing have MRI features that are atypical for their specific disease. The appearance of specific MRI patterns depends on the stage of the disease and the patient's age at evaluation. MRI interpretation can be challenging because of heterogeneously acquired MRI datasets, individual interpreter bias, and lack of quantitative data. Therefore, optimal acquisition and interpretation of MRI data are needed to better define MRI phenotypes in NBIA disorders. The stepwise approach outlined here may help to identify NBIA disorders and delineate the natural course of MRI-identified changes.

The pallidopyramidal syndromes: nosology, aetiology and pathogenesis

Purpose of review

The aims of this review is to suggest a new nomenclature and classification system for the diseases currently categorized as neurodegeneration with brain iron accumulation (NBIA) or dystonia-parkinsonism, and to discuss the mechanisms implicated in the pathogenesis of these diseases.

Recent findings

NBIA is a disease category encompassing syndromes with iron accumulation and prominent dystonia–parkinsonism. However, as there are many diseases with similar clinical presentations but without iron accumulation and/or known genetic cause, the current classification system and nomenclature remain confusing. The pathogenetic mechanisms of these diseases and the causes of gross iron accumulation and significant burden of neuroaxonal spheroids are also elusive. Recent genetic and functional studies have identified surprising links between NBIA, Parkinson's disease and lysosomal storage disorders (LSD) with the common theme being a combined lysosomal–mitochondrial dysfunction. We hypothesize that mitochondria and lysosomes form a functional continuum with a predominance of mitochondrial and lysosomal pathways in NBIA and LSD, respectively, and with Parkinson's disease representing an intermediate form of disease.

Summary

During the past 18 months, important advances have been made towards understanding the genetic and pathological underpinnings of the pallidopyramidal syndromes with important implications for clinical practice and future treatment developments.

Eye-of-the-tiger-sign in a 48 year healthy adult

We report a healthy adult male, who underwent, as a control subject, part of a Huntington's disease study, extensive testing during three visits in a two year follow-up, including clinical examination and 3.0 T MRI scans. The T2-weighted MRI sequences revealed the "eye-of-the-tiger-sign". No clinical abnormalities in either motor, cognitive or behavioural domains were observed. PKAN2 and FTL gene mutation analysis were negative. This finding implies that an eye-of-the-tiger sign, which is considered a pathognomonic feature of neurodegeneration with brain iron accumulation (NBIA), can occur without any clinical symptoms.

Late onset neurodegeneration with brain-iron accumulation presenting as parkinsonism

Neurodegeneration with brain-iron accumulation (NBIA) encompasses a family of neurodegenerative disorders connected by evidence of abnormal brain iron deposition. Advances in imaging and genetic testing expanded the clinical spectrum of these disorders. Here, a case of parkinsonism and dystonia with orofacial stereotypies is presented. While the patient was initially diagnosed with Parkinson's disease and placed on levodopa therapy, dopamine transporter imaging via (123)I-FP-CIT SPECT (DaTSCAN) was normal. MRI brain showed "eye of the tiger" sign on T2 weighted imaging. NBIA should be considered in the differential diagnosis of atypical parkinsonism.

Genetics and Pathophysiology of Neurodegeneration with Brain Iron Accumulation (NBIA)

Our understanding of the syndromes of Neurodegeneration with Brain Iron Accumulation (NBIA) continues to grow considerably. In addition to the core syndromes of pantothenate kinase-associated neurodegeneration (PKAN, NBIA1) and PLA2G6-associated neurodegeneration (PLAN, NBIA2), several other genetic causes have been identified (including FA2H, C19orf12, ATP13A2, CP and FTL). In parallel, the clinical and pathological spectrum has broadened and new age-dependent presentations are being described. There is also growing recognition of overlap between the different NBIA disorders and other diseases including spastic paraplegias, leukodystrophies and neuronal ceroid lipofuscinosis which makes a diagnosis solely based on clinical findings challenging. Autopsy examination of genetically-confirmed cases demonstrates Lewy bodies, neurofibrillary tangles, and other hallmarks of apparently distinct neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease. Until we disentangle the various NBIA genes and their related pathways and move towards pathogenesis-targeted therapies, the treatment remains symptomatic. Our aim here is to provide an overview of historical developments of research into iron metabolism and its relevance in neurodegenerative disorders. We then focus on clinical features and investigational findings in NBIA and summarize therapeutic results reviewing reports of iron chelation therapy and deep brain stimulation. We also discuss genetic and molecular underpinnings of the NBIA syndromes.

Syndromes of neurodegeneration with brain iron accumulation

In parallel to recent developments of genetic techniques, understanding of the syndromes of neurodegeneration with brain iron accumulation has grown considerably. The acknowledged clinical spectrum continues to broaden, with age-dependent presentations being recognized. Postmortem brain examination of genetically confirmed cases has demonstrated Lewy bodies and/or tangles in some forms, bridging the gap to more common neurodegenerative disorders, including Parkinson disease. In this review, the major forms of neurodegeneration with brain iron accumulation (NBIA) are summarized, concentrating on clinical findings and molecular insights. In addition to pantothenate kinase-associated neurodegeneration (PKAN) and phospholipase A2-associated neurodegeneration (PLAN), fatty acid hydroxylase-associated neurodegeneration (FAHN) NBIA, mitochondrial protein-associated neurodegeneration, Kufor-Rakeb disease, aceruloplasminemia, neuroferritinopathy, and SENDA syndrome (static encephalopathy of childhood with neurodegeneration in adulthood) are discussed.

Movement disorders: role of imaging in diagnosis

Magnetic resonance imaging (MRI and single-photon emission computed tomography (SPECT) have a considerable role in the diagnosis of the single patient with movement disorders. Conventional MRI demonstrates symptomatic causes of parkinsonism but does not show any specific finding in Parkinson's disease (PD). However, SPECT using tracers of the dopamine transporter (DAT) demonstrates an asymmetric decrease of the uptake in the putamen and caudate from the earliest clinical stages. In other degenerative forms of parkinsonism, including progressive supranuclear palsy (PSP), multisystem atrophy (MSA), and corticobasal degeneration (CBD), MRI reveals characteristic patterns of regional atrophy combined with signal changes or microstructural changes in the basal ganglia, pons, middle and superior cerebellar peduncles, and cerebral subcortical white matter. SPECT demonstrates a decreased uptake of tracers of the dopamine D2 receptors in the striata of patients with PSP and MSA, which is not observed in early PD. MRI also significantly contributes to the diagnosis of some inherited hyperkinetic conditions including neurodegeneration with brain iron accumulation and fragile-X tremor/ataxia syndrome by revealing characteristic symmetric signal changes in the basal ganglia and middle cerebellar peduncles, respectively. A combination of the clinical features with MRI and SPECT is recommended for optimization of the diagnostic algorithm in movement disorders.