Correspondence
Neuroradiographic Manifestations of Encephalitis
N Engl J Med 1997; 337:1393-1394November 6, 1997
- Article
To the Editor:
In their paper on neuroradiographic manifestations of eastern equine encephalitis, Deresiewicz et al. (June 26 issue)1 report on the predilection of this disease for the basal ganglia, thalami, and brain stem. We would like to add another arboviral infection that can occur in areas in Europe in which the disease is endemic — namely, tick-borne encephalitis — to the differential diagnoses of basal ganglionic and thalamic lesions on magnetic resonance imaging (MRI) in patients with encephalitis. The virus is transmitted by ticks of the species Ixodes ricinus. Neuropathological studies stress the prominent involvement of the basal ganglia and thalami in tick-borne encephalitis,2 and MRI can reveal pronounced lesions in the thalamus and basal ganglia during the disease.3,4 We have recently seen another patient with tick-borne encephalitis who had marked involvement of the thalami (Figure 1Figure 1
T2-Weighted Magnetic Resonance Image (MRI) of a 55-Year-Old Patient with Severe Tick-Borne Encephalitis.). Thus, tick-borne encephalitis must be added to the differential diagnosis of patients with encephalitis who are from an area in which the disease is endemic and who have abnormalities predominantly of the thalami and basal ganglia on MRI.4 ReferencesHans-Walter Pfister, M.D.
Stefan Lorenzl, M.D.
Tarek Yousry, M.D.
Ludwig Maximilians University, D-81377 Munich, Germany1
Deresiewicz RL ,Thaler SJ ,Hsu L ,Zamani AA . Clinical and neuroradiographic manifestations of eastern equine encephalitis. N Engl J Med 1997;336:1867-1874
Full Text | Web of Science | Medline2
Jellinger K. The histopathology of tick-borne encephalitis. In: Kunz TH, ed. Tick-borne encephalitis. Vienna, Austria: Facultas-Verlag, 1981:59-75.
3
Lorenzl S ,Pfister HW ,Padovan C ,Yousry T . MRI abnormalities in tick-borne encephalitis. Lancet 1996;347:698-699
CrossRef | Web of Science | Medline4
Valdueza JM ,Weber JR ,Harms L ,Bock A . Severe tick borne encephalomyelitis after tick bite and passive immunisation. J Neurol Neurosurg Psychiatry 1996;60:593-594
CrossRef | Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: We agree with Pfister et al. that tick-borne encephalitis should be considered in the differential diagnosis of basal ganglionic and thalamic lesions in patients with encephalitis acquired in an area in which the disease is endemic. Tick-borne encephalitis is caused by a flavivirus and is phylogenically related to the mosquito-borne eastern equine encephalitis alphavirus. Like eastern equine encephalitis, tick-borne encephalitis can cause very severe encephalitis and substantial morbidity and mortality.
Three arboviral encephalitides (eastern equine encephalitis, tick-borne encephalitis, and Japanese encephalitis) have now been associated with basal ganglionic and thalamic abnormalities on MRI.1 Whether this pattern is attributable to focal viral neurotropism, to enhanced susceptibility of neurons in those areas of the brain to viral injury, or to other factors remains to be determined. The temporal evolution of the lesions appears to differ somewhat in these three diseases, however, suggesting that they may derive from dissimilar pathogenic mechanisms. In our series, four patients in whom serial MRIs were available had substantial radiographic improvement over a period of one to two weeks; the presence of large lesions did not predict a poor outcome. We suspect that the lesions represent ischemia, inflammation, or edema, at least initially, rather than necrosis.
From the limited data available on patients with Japanese encephalitis2 or tick-borne encephalitis,3,4 it appears that the abnormalities in such patients are substantially more persistent, improving over a period of weeks in the case of tick-borne encephalitis and lasting even years in the case of Japanese encephalitis. These abnormalities are therefore more likely to reflect fixed tissue damage than readily reversible phenomena. Alternatively, the apparent differences may simply reflect selection bias. Additional data correlating MRI findings with the outcome and pathological findings may clarify this issue.
4 ReferencesScott J. Thaler, M.D.
Robert L. Deresiewicz, M.D.
Harvard Medical School, Boston, MA 021151
Deresiewicz RL ,Thaler SJ ,Hsu L ,Zamani AA . Clinical and neuroradiographic manifestations of eastern equine encephalitis. N Engl J Med 1997;336:1867-1874
Full Text | Web of Science | Medline2
Shoji H ,Murakami T ,Murai I , et al. A follow-up study by CT and MRI in 3 cases of Japanese encephalitis. Neuroradiology 1990;32:215-219
CrossRef | Web of Science | Medline3
Lorenzl S ,Pfister HW ,Padovan C ,Yousry T . MRI abnormalities in tick-borne encephalitis. Lancet 1996;347:698-699
CrossRef | Web of Science | Medline4
Valdueza JM ,Weber JR ,Harms L ,Bock A . Severe tick borne encephalomyelitis after tick bite and passive immunisation. J Neurol Neurosurg Psychiatry 1996;60:593-594
CrossRef | Web of Science | Medline
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