Movement Disorders

Winter 1998-1999
Volume 9, Number 2

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Neuroimaging can provide useful information for the evaluation and monitoring of patients with movement disorders. The distribution of trace paramagnetic substances – particularly iron – with the extrapyramidal system can be accurately assessed with magnetic resonance imaging (MRI). Abnormalities of iron distribution can provide keys to aid in differential diagnosis. Neuroimaging also plays an important role in excluding other central nervous system pathology, which may mimic the more common causes of movement disorders.

Introduction. Neuroimaging has always played an important role in the diagnosis and management of patients with movement disorders. Despite the heterogeneous neuropathic features of movement disorders, imaging the anatomic and functional characteristics remains an important clinical tool. Early attempts at differentiating the various disorders by imaging utilized pneumoencephalography to search for unique anatomic changes. The subtle alterations in anatomy were difficult to appreciate with what is considered by today’s standards a crude tool. The introduction of computed tomography (CT) brought with it a flurry of reports on the subtle anatomic changes, primarily related to specific patterns of atrophy, associated with the various movement disorders. With the advent of magnetic resonance imaging (MR), the neuroimaging of patients with movement disorders was revolutionized. Magnetic resonance images are affected by the presence of small amounts of naturally occurring paramagnetic substances — primarily iron — which delineate the neostriatum (caudate and putamen), globus pallidus, red nucleus, substantia nigra, and dentate nucleus.1 These paramagnetic substances are made apparent by the T2* effect. Contrast is created by local inhomogeneities in the magnetic field, which cause spin dephasing, and subsequent signal void (Koenig). This effect is best appreciated with gradient echo sequences, but is readily apparent on conventional spin echo T2 weighted sequences. The area of relative decreased signal on T2 weighted images roughly correspond to the distribution of ferric iron demonstrated by Perls’ Prussian blue stain.2 (Figure 1) There is a characteristic distribution of brain iron that varies with age; none is present at birth, then a rapid accumulation occurs with the majority being present between the ages of 8 and 25 years. After this, gradual accumulation occurs, predominantly in the globus pallidus, putamen, and substantia nigra in old age. A unique characteristic of the extrapyramidal system is that its nuclei contain high concentrations of iron, particularly globus pallidus and substantia nigra. Lesser amounts are found in the red nucleus, dentate nucleus, nigrostriatal tract, putamen, caudate nucleus, and the fifth layer of cortical gray matter. The reasons for increased iron in nuclei related to movement are unknown.

Figure 1 Missing

Magnetic resonance imaging’s accurate portrayal of neuroanatomy allows for detection of subtle changes in brain volume, which may reflect atrophy. The evaluation of brain iron also provides an important tool for evaluating and diagnosing patients with movement disorders. Additional functional imaging tools, such as radionuclide cisternography, single photon emission computed tomography (SPECT), and magnetic resonance spectroscopy (MRS) may also play an important role. Stereotactic MR provides accurate localization for targeted therapy in select patients.

Neuroimaging in Parkinson’s Disease and Parkinsonism. The heterogeneous group of akinetic-rigid syndromes includes Parkinson’s Disease, secondary parkinsonisms, and parkinsonisms with other heterogeneous system disorders of Parkinson plus syndrome. This third group contains several diseases including progressive supranuclear palsy, olivo-ponto-cerebellar atrophy, Shy-Drager syndrome and striatonigral degeneration. Differentiating these entities with MR can be difficult, but the MR exam can provide clues. In Parkinson’s Disease, there is a relatively inconstant finding of increased signal within the dorsal lateral aspect of the substantia nigra (pars compacta) on T2 weighted images. The normal low signal seen in this region due to iron deposition is reversed and similar to signal in the adjacent brainstem. This finding is relatively specific to parkinsonisms, but does not differentiate Parkinson’s Disease from parkinsonisms secondary to other causes, such as infection, toxin- or drug-induced trauma or infarction. There is however an excellent correlation with parkinsonism secondary to stroke. These patients will show ischemic signal change, typically at the level of the decussation of the brachium conjunctivum or upper pons. In patients with Parkinson’s plus syndrome, both iron distribution and pattern of focal atrophy can provide clues. Patients with progressive supranuclear palsy show a fairly typical pattern of midbrain atrophy, with concurrent dilatation of the aqueduct, quadrigeminal plate cistern, and posterior portion of the third striatonigial degeneration ventricle (Rutledge). Patients with olivo-ponto-cerebellar atrophy and Shy-Drager syndrome show atrophy of the pons, olives, brachium pontis, medulla, and cerebellum. Patients with these multi system atrophy syndromes will often have increased signal within the globus pallidus and posterior putamen. In all of the Parkinson’s plus syndromes there is often decrease in signal in the putamen due to increased iron deposition relative to the normal decreased signal in the adjacent globus pallidus. In these patients there may also be decreased signal in the pars compacta of substantia nigra.3 Although the imaging findings in the parkinsonisms are not entirely specific, they can detect patients who may not benefit from conventional anti-parkinsonism therapy, such as patients with Parkinson’s plus syndromes.

Normal Pressure Hydrocephalus. Normal pressure hydrocephalus (NPH) has classically been described by the clinical trial of gait disturbance, dementia, and urinary incontinence. Not all elderly patients with gait disturbance due to NPH display the complete triad. The initial screening exam is usually a cranial CT, showing disproportionate enlargement of ventricles relative to cortical sulcal dilatation. This initial exam will also exclude many other causes, such as frontal lobe tumors. In patients with enlarged ventricles by CT, and no other concomitant findings, the subsequent diagnostic paradigm remains controversial. Most would agree that MR examination is useful to exclude other subtle causes, such as ischemic injury, ie, Binswanger’s disease. If the MR fails to yield an alternative underlying diagnosis, and further confirms the suspicion of NPH by demonstrating normal or augmented flow through the aqueduct and/or no obstructive ventricular lesion, the next potential confirmatory diagnostic exam is radionuclide cisternography. Although not entirely specific, demonstration of the typical flow pattern seen with NPH will often help confirm the diagnosis. After ventricular shunting is performed, CT is useful for excluding complications of the procedure, such as formation of subdural hygromas or hematomas. The size of the ventricular system demonstrated by post-shunting cranial CT shows an imperfect correlation with clinical improvement. Nuclear medicine studies have not been predictive of response to shunting.

Neuroimaging of Patients with Dystonia. Neuroimaging provides little specificity in the primary or inherited dystonias. There is however a fairly good correlation between MR characteristics and cause of secondary dystonias. A good example is Wilson’s disease, where abnormal deposition of copper results in a characteristic pattern of decreased signal in the putamen. Patients with Hallervorden-Spatz disease will show a typical pattern of abnormal decreased signal within the globus pallidus due to abnormal iron deposition, despite the pathologic features of pallidal gliosis, demyelination and axonal loss, features which usually cause increased T2 signal. In other secondary causes of dystonia, such as Leigh’s disease, glutaric aciduria, post-infection, or post-ischemic dystonia, neuroimaging will often provide confirmatory diagnosis due to specific localization of an anatomic lesion within the extrapyramidal system.

Neuroimaging in Choreic Disorders and Hemiballismus. The prototypic choreic disorder is Huntington’s disease. Recent advances in genetic detection of this disorder have made MR imaging less useful. Patients with Huntington’s disease show early MR findings of increased signal within the caudate nucleus, followed by progressive loss of volume with resulting lateral dilatation of the frontal horns of the lateral ventricles. Magnetic resonance spectroscopy is currently being investigated as an additional tool for detection and monitoring disease progress.

Hemiballismus is a rare disorder and is almost always caused by a lesion near the contralateral subthalamic nucleus although multiple sub-cortical structures may be involved. These lesions may be neoplastic, ischemic or hemorrhagic. The sensitivity of MR imaging will provide confirmatory localization of the lesion in almost all cases, and the specificity of MR and MRS will often provide the specific diagnosis.

Conclusion. Currently available neuroimaging techniques allow clinicians to diagnose movement disorders accurately. At CNI, the most important uses of MRI include evaluation of secondary causes of movement disorders and as an aid in stereotactic surgery. Development of functional imaging techniques and metabolic imaging using SPECT scans and new labeled isotopes will lead CNI into the future with cutting edge technology.

Address comments and questions to:

Erin C Prenger, DO
Radiology Imaging Associates
3333 South Bannock Street, Suite 600
Englewood, CO 80113

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