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Neurology

Volume 48 . Number 3 . March 1997

Copyright © 1997 American Academy of Neurology

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MRI in sporadic olivopontocerebellar atrophy and striatonigral degeneration

To the Editor:

We read with interest the review by Gilman and Quinn on the relationship of

multiple system atrophy (MSA) to sporadic olivopontocerebellar atrophy

(sOPCA). [1] We are amazed, however, at the reluctance of neurologists to

accept the support of MRI in diagnosing these conditions.

We agree that mild cerebellar and pontine atrophy may be of questionable

significance and insufficient to establish a diagnosis. However, when in

addition to atrophy of the cerebellum, pons, and middle cerebellar peduncles

there are signal abnormalities in the structures known to degenerate in

sOPCA, the diagnosis, in our opinion, becomes definite. In sOPCA the pontine

nuclei and the fibers running from them to the cerebellum through the middle

cerebellar peduncles (transverse pontine fibers) degenerate; so, too, do the

Purkinje cells and their fibers to the dentate nuclei. The fibers that

originate in the dentate nuclei and form the superior cerebellar peduncles

remain intact; the pyramidal fibers are also normal. Therefore, in

histologic sections through the pons stained for myelin, one observes poor

staining, or no staining at all, at the anterior and lateral surfaces of the

pons, the posterior part of the basis pontis, the raphe (where the

transverse pontine fibers run and cross), and the middle cerebellar

peduncles, where these fibers merge into the cerebellum. On the other hand,

the superior cerebellar peduncles and the pyramidal tracts are conspicuous

by their normal staining. [2] This distribution exactly matches the signal

abnormalities seen in proton density and T2 -weighted images. [3] [4]

Sometimes signal abnormalities are also observed in the inferior olives.

This pattern has never been observed by us in other cerebellar degenerative

disorders and is, we contend, specific for sOPCA (figure 1) .

MRI also shows characteristic abnormalities in striatonigral degeneration

(SND). In SND, the MRI findings at high field intensity (1.5 T) differ from

those at lower field (0.5 T). In high field MRI, putaminal hypointensity in

T2 -weighted images is evident, mainly posteriorly, and correlates with the

presence of iron and other paramagnetic substances (manganese, neuromelanin,

hematin pigments). [5] [6] A thin rim of high signal intensity may be seen

in the most lateral part of the putamen. [4] In low field MRI, the magnetic

susceptibility effects of iron are scarcely evident, and hypointensity may

be completely absent. Therefore, high signal intensity in T2 -weighted

images caused by increased water content, related to cell loss and gliosis,

is not masked and is in fact the characteristic abnormality of SND at low

field. [3] [4] [7]

In the early stages of SND when parkinsonian features may be asymmetric, MRI

abnormalities will be evident only in the hemisphere contralateral to the

affected side (figure 2) .

In MSA patients with both cerebellar and extrapyramidal signs, MRI shows

abnormalities in the posterior fossa and in the basal ganglia, thus

confirming the involvement of both systems. [3] [4]

Figure 1. (A and Axial proton density spin-echo MR images (TR 2,000/TE

20) in sOPCA. Increased signal intensity is present in the transverse

pontine fibers, middle cerebellar peduncles, and cerebellum (compare

cerebellum with the normal occipital lobes in . The pyramidal tracts also

have normal signal intensity.

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Figure 2. Coronal T2 -weighted spin-echo MR image (TR 2,000/TE 90) in SND

at 1.5 T. A patient with recent onset of parkinsonian features on the right

side exhibits abnormal hypointensity in the left putamen.

We have observed these abnormalities in more than 100 patients; their

excellent correlation with clinical findings [8] has induced us to consider

them necessary to establish the diagnosis. Furthermore, they are present

early enough in the course of the disease to be of clinical value.

M. Savoiardo MD

M. Grisoli MD

F. Girotti MD

D. Testa MD

T. Caraceni MD

Milan, Italy

Reply from the Authors:

We thank Dr. Savoiardo et al for their interest in our review and

acknowledge their group's major contribution to the delineation of multiple

system atrophy (MSA), particularly the neuroradiologic features.

On clinical presentation, most MSA patients predominantly have signs of

extrapyramidal disease with or without accompanying signs of cerebellar

disorder. We use the term striatonigral degeneration (SND)-type MSA for

these patients. A smaller proportion show chiefly signs of cerebellar

disease, and some of these patients show additional signs of extrapyramidal

disorder. We use the term olivopontocerebellar atrophy (OPCA)-type MSA for

these patients. Our review [1] deliberately addressed the difficult subject

of the diagnosis of sporadic OPCA (sOPCA) and the question of whether some,

most, or all of these patients have MSA.

In SND-type MSA, which we did not address specifically, putaminal

hypointensity (relative to globus pallidus) on 1.0- to 1.5-tesla

T2 -weighted MR images has indeed been demonstrated in a number of patients,

[8] [9] including some with pathologic confirmation of the diagnosis. [10]

[11] [12] Putaminal hypointensity has also been described in some OPCA-type

MSA patients. [8] In our experience and that of others, however, many MSA

patients, even those of SND-type, do not show this finding. [13] [14]

Moreover, putaminal hypointensity also has been reported in some patients

with clinically typical idiopathic Parkinson's disease [15] and in some with

a clinical diagnosis of progressive supranuclear palsy. [9]

Slit-like hyperintensity of the lateral putaminal border has been found with

0.5-, 1.0-, and 1.5-tesla MR imaging of many patients with SND-type MSA,

again with pathologic confirmation in a few of them, [10] [11] [12] and in a

few with OPCA-type MSA. [8] [15] Nevertheless, many patients we have seen

with SND- and OPCA-type MSA have neither putaminal hypointensity on

1.5-tesla T2 -weighted scans nor slit-like hyperintensity on either 0.5- or

1.5-tesla scans, and other investigators have had the same experience. [13]

[14] Savoiardo et al state that in SND, putaminal hypointensity " is

evident, " slit-like hyperintensity " may be seen " and that in MSA patients

with signs of both cerebellar and extrapyramidal disease, " MRI shows

abnormalities in the posterior fossa and the basal ganglia. " They conclude

that the excellent correlation of MRI abnormalities with clinical findings

leads them to consider the findings in neuroimaging as " necessary to

establish the diagnosis. " We submit that insisting on the presence of these

changes for a diagnosis creates a potentially circular and self-fulfilling

prophecy that all MSA patients have diagnostic MRI changes, which is clearly

not the case. Moreover, accepting their dictum will exclude many cases of

MSA, particularly patients relatively early in the course of their disease.

We are not, as they suggest, " reluctant to accept the support " of MRI in the

diagnosis of MSA. On the contrary, positive findings in MRI are helpful, but

negative results do not rule out the diagnosis. For clinicians, the

diagnosis of MSA during life remains clinical and is made in practice every

day without requiring these MRI abnormalities. The MRI abnormalities offer

support for the diagnosis when present, but the abnormalities lack

sensitivity and are probably not specific for the diagnosis.

The findings with MRI can be helpful in assessing patients with sporadic

idiopathic late-onset cerebellar ataxia (ILOCA). As we pointed out in our

review, the demonstration by MRI of cerebellar atrophy alone is of little

help in differential diagnosis, but additional pontine atrophy helps by

placing the patient into the category of sOPCA. We have rarely encountered

convincing increased signal intensity in the transverse pontine fibers,

middle cerebellar peduncles, and cerebellum (as seen in figure 1) in such

cases. Moreover, one of the main points of our review is that currently it

is uncertain whether all sOPCA patients or only some have MSA. Additional

putaminal changes probably make OPCA-type MSA likely, but at present we do

not have enough evidence to confirm this. Hence, in our article we appealed

for more cases with good clinicopathologic correlation.

Although we agree that certain MRI findings lend support to a diagnosis of

either SND or OPCA-type MSA, we see no justification for insisting that

these abnormalities are a necessary criterion for these diagnoses. Moreover,

we consider the evidence to be inconclusive as to whether sOPCA is one

disease (MSA), two diseases (including MSA), or more.

Sid Gilman MD

Ann Arbor, MI

Niall P. Quinn MD

London, United Kingdom

References

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8. Testa D, Savoiardo M, Fetoni V, et al. Multiple system atrophy: clinical

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