J Neurol Neurosurg Psychiatry 2003;74:1444–1446

D A S Compston
Neurology Unit, University of Cambridge,
Addenbrooke’s Hospital, Hills Road, Cambridge CB2
2QQ, UK
Correspondence to: Dr Robertson:
robertsonnp@cardiff.ac.uk

References
1 Harding AE. Clinical features and classification of
inherited ataxias. Adv Neurol 1993;61:1–14.
2 Cummings CJ, Zoghbi HY. Fourteen and
counting: unravelling trinucleotide repeat
diseases. Hum Mol Genet 2000;9:909–16.
3 Sethi KD, Jankovic J. Dystonia in spinocerebellar
ataxia type 6. Mov Disord 2002;17:150–3.
4 Zhuchenko O, Bailey J, Bonnen P, et al.
Autosomal dominant cerebellar ataxia
(spinocerebellar 6) associated with small
polyglutamine expansion in the alpha 1Avoltage-dependent calcium channel. Nat Genet
1997;15:62–69.
5 Jen JC, Yue Q, Karrim J, et al. Spinocerebellar
ataxia type 6 with positional vertigo and
acetazolamide responsive episodic ataxia.
J Neurol Neurosurg Psychiatry 1998;65:565–8.
6 Schols L, Peters S, Szymanski S, et al.
Extrapyramidal motor signs in degenerative
ataxias. Arch Neurol 2000;57:1495–500.

Bilateral cerebellar ataxia as the
sole manifestation of a unilateral
rostral pontine tegmental infarct
It has been reported that a small infarct of
the pons can lead to various clinical syndromes such as pure motor hemiparesis,
sensorimotor stroke, ataxic hemiparesis, dysarthria-clumsy hand syndrome, or ataxic
tetraparesis.1 However, bilateral, cerebellar
ataxia as the sole manifestation of rostral
pontine tegmental infarction has not been
described. We report a patient with isolated
bilateral cerebellar ataxia as the only sign of a
rostral pontine tegmental infarct. This unique
presentation reflected the selective involvement of part of the decussation of the
superior cerebellar peduncle.

Case report
A 51 year old man with hypertension developed acute severe imbalance. On examination, he tended to fall to the right when
standing unsupported with eyes open. He did
not have dysarthria, limb weakness, vertigo,

Figure 1 Brain magnetic resonance imaging:
an axial T2 weighted image showing a right
paramedian infarct of lacuna size situated in
the tegmentum of the most rostral pons.

nystagmus, ophthalmoparesis, diplopia, sensory loss, or Horner’s syndrome. The muscle
stretch reflexes were normal and the plantar
reflexes were flexor bilaterally. There was
severe dysmetria on finger-to-nose and heelto-shin testing on both sides. Dysmetria was
worse on the right. The results of somatosensory evoked potentials, brain stem auditory evoked potentials, and pure tone
audiography were unremarkable. There were
no abnormalities of horizontal saccades,
smooth pursuit, optokinetic nystagmus, or
caloric responses.
Brain magnetic resonance imaging (MRI)
showed a right paramedian infarct of lacunar
size situated in the tegmentum of the most
rostral pons, corresponding to part of the
decussation of the superior cerebellar peduncle (fig 1). Magnetic resonance angiography
(MRA) showed no abnormalities. An ECG
and transoesophageal echocardiography with
a bubble study revealed no abnormalities.
The limb coordination and gait improved
steadily over several days, but there was mild
dysmetria on the heel-to-shin test on the
right side. On discharge, the patient complained only of mild unsteadiness when
walking.

Comment
There have been several reports of bilateral
cerebellar ataxia caused by a unilateral brain
stem stroke.2–7 However, previous reports
have also described associated neurological
symptoms such as mild hemiparesis, dysarthria, sensory change in an extremity, or
multiple cranial nerve palsy.
Without pathological confirmation, it is
difficult to be certain that the infarct affected
only the structure identified (the superior
cerebellar peduncle). However, in the rostral
pons, the only anatomical structure responsible for bilateral limb ataxia is the superior
cerebellar peduncle, which is situated in the
dorsolateral side to the fourth ventricle and
medial to the lateral lemniscus at the level of
the most rostral pons—that is, at isthmus
level.8 From at this level, the fibres of the
superior cerebellar peduncle move ventromedially towards their decussation. Serial neurological examinations over a period of days
did not show any neurological signs except
bilateral ataxia. These clinical data, when
correlated with the known cross sectional
anatomy of the most rostral part of the pons,
suggest that the small lesion of our patient on
brain MRI corresponded to part of the
decussation of the superior cerebellar peduncle. Thus the isolated bilateral cerebellar
ataxia in our patient may be explained by
ipsilateral involvement of both efferent cerebellar pathways. These which include
uncrossed fibres of the superior cerebellar
peduncle ipsilateral to the lesion and crossed
fibres arising contralateral to the lesion.
From the results of MRA and transoesophageal echocardiography, risk factor
analysis, and the size of an infarct on brain
MRI, small artery disease (that is, a lacunar
stroke) was considered the likely pathogenesis.
In summary, our patient presented with
isolated bilateral cerebellar ataxia caused by a
small infarct situated in the rostral pontine
tegmentum. This unique presentation may
result from ipsilateral involvement of both
efferent cerebellar pathways, before and after
the decussation of the superior cerebellar
peduncle. We have previously reported isolated ataxia as the sole manifestation of

1445

lateral medullary infarction.9 Together, these
reports highlight the importance of sudden
gait disturbance as the sole manifestation of
brain stem stroke. Rostral pontine paramedian tegmental infarction should be considered in the differential diagnosis of sudden
bilateral cerebellar ataxia, even when classic
brain stem signs are absent.
H Lee, Y-W Cho
Department of Neurology, and Brain Research
Institute, Keimyung University School of Medicine,
Daegu, South Korea
Correspondence to: Dr H Lee, Department of
Neurology, Keimyung University School of Medicine,
194 Dongsan dong, Daegu 700-712, South Korea;
hlee@dsmc.or.kr

References
1 Fisher CM. Lacunar infarcts. A review.
Cerebrovasc Dis 1991;1:311–20.
2 Caplan LR, Goodwin JA. Lateral tegmental
brainstem hemorrhage. Neurology
1982;32:252–60.
3 Van Gijn J, Vermeulen M. Ataxic tetraparesis
from lacunar infarction in the pons. J Neurol
Neurosurg Psychiatry 1983;46:669–70.
4 Bogousslavsky J, Maeder P, Regli F, et al. Pure
midbrain infarction: clinical syndromes, MRI, and
etiologic patterns. Neurology 1994;44:2032–40.
5 Kim JS, Lee JH, Im JH, et al. Syndrome of pontine
base infarction: a clinical-radiological correlation
study. Stroke 1994;26:950–5.
6 Withiam-Leitch S, Pullicino P. Ataxic hemiparesis
with bilateral leg ataxia from pontine infarct.
J Neurol Neurosurg Psychiatry 1995;59:557–8.
7 Krespi Y, Aykutlu E, Coban O, et al. Internuclear
ophthalmoplegia and cerebellar ataxia: report of
one cases. Cerebrovasc Dis 2001;12:346–8.
8 Parent A, ed. Carpenter’s human anatomy, 9th
ed. Baltimore: Williams and Wilkins,
1996:507–11.
9 Lee H, Sohn CH. Axial lateroplusion as a sole
manifestation of lateral medullary infarction: a
clinical variant related to rostral-dorsolateral
lesion. Neurol Res 2002;24:773–4.

Identification of amoebae in the
CSF in a patient with
meningoencephalitis
Amoebae are amphizoic, ubiquitous, and
opportunistic protozoa that can affect different organs including skin, lungs, eyes, and
the brain.1 2 In the central nervous system
(CNS), two main, well defined disease
entities have been described: primary amoebic meningoencephalitis, which is caused by
Naegleria fowlery and is rapidly fatal, and
granulomatous amoebic encephalitis, which
is caused by Acanthamoeba spp and
Balamuthia mandrillaris and is characterised
by focal granulomatous lesions in the brain
following a subacute or chronic course. CNS
infections caused by free living amoebae are
uncommon and, as of October 1996, for
example, only 166 cases of granulomatous
amoebic encephalitis have been reported
from around the world.1 Identification of
amoebae in cerebrospinal fluid (CSF) samples is a rare event.1 2
We have recently seen a patient with
meningoencephalitis in whom amoebic forms
were identified in the CSF. She was a 48 year
old woman who was admitted to our
neurological clinic because of vertigo, headache, bilateral hypacusia, ataxia, diplopia,
dysphonia, dysphagia, anosmia, ageusia, tetraparesis, occurrence of transient clonic fits
in the right upper limb, and vomiting
episodes. The onset of her illness dated from
about six weeks earlier, when she began to

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