Letter to the editor

Latent or truly asymptomatic multiple sclerosis

Engell suggests (1) that every fourth case of multiple sclerosis goes undetected - or at least does not come to medical attention. In contrast, Georgi (3) reported only 2 of 66 MS cases among 15,644 autopsies in which no evidence of neurologic deficit could be obtained from reviewing the medical history and examination, while in 20 cases neurologic deficits had not been correctly diagnosed as MS during life time.

The rate of 25% of silent MS reported by Engell is of particular interest since with the increasing availability of magnetic resonance imaging a growing number of patients are scanned. Not infrequently are we faced with signal intensities on magnetic re- sonance images that could represent MS plaques as the only finding (2). However, it would be of utmost interest to learn more about the prognosis of patients displaying such abnormalities.

Unfortunately the author did not mention the age, medical history or causes of death of the 15 cases in question. She does mention that pathological exami- nation was performed because of malignant or cere- brovascular disease but detailed patient data were not provided.

It would be important to know the mean age and range in this autopsy study and in those cases showing MS plaques in order to see whether these plaques represent truly asymptomatic MS that has not become symptomatic within normal life expec- tancy or latent MS that has not had the chance to progress to a clinically patent form because the affficted patient died young.

Stefan Knecht, Bernd Frank Hannover Medical School West Germany

References

ENGELL T. A clinical patho-anatomical study of clinically silent multiple sclerosis. Acta Neurol Scand 1989: 79: 428-30. JACOBS L, KINKEL PR, KINKEL WR. Silent brain lesions in patients with isolated optic neuritis. Arch Neurol 1986: 43:

GEORGI VW. Pathologisch-Anatomische Befunde multipler Sklerose bei klinisch nicht diagnostizierten Krankheiten. Schweiz Med Wochenschr 1961: 605-7.

452-5.

Reply

The question is whether the subjects with clinically silent MS had possibly died before they had the chance of progressing to overt (manifest) disease.

As judged from the ages in the group, this is not likely. Those with clinically silent MS had a mean age at death of 67 years. Only one subject died young, at the age of 32 years. The series contained 13 cases of clinically silent MS.

Reviewing the records of the 468 consecutive MS cases from the very same period verified at autopsy, the mean age at death was 54 years. Accordingly, the silent cases had an excess lifetime of more than a decade for developing symptoms, which they did not; MS debut after the age of 67 years is indeed rare.

The 13 subjects made up 0.08% of all having had neuropathological evaluation at autopsy. Using this percentage on a full annual sample of deaths in Denmark, the figure of 1 silent case per 3-4 with clinically acknowledged MS is arrived at.

Of course one has to be careful when assessing large scale on the basis of small samples and low percentages. The present estimate should be con- sidered gross only. Other materials may lead to higher estimates of silent MS.

I am happy that your question draws attention to clinically silent MS. To me these cases open up a new field of scientific research and it may be that clinically silent MS represents heterogeneity of MS.

Tine Engell

References

1. ENGELL T. A clinico-pathoanatomical study of multiple scle- rosis diagnosis. Acta Neurol Scand 1988: 78: 39-44.

2. ENGELL T. A clinical patho-anatomical study of clinically silent multiple sclerosis. Acta Neurol Scand 1989: 79: 428-430.

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