MS clusters: chance or design? - multiple sclerosis

Inside MS, Summer, 1989 by Phyllis Shaw

MS Clusters; Chance or Design?

Whenever a story of a "cluster" breaks in the media, the telephones at the Society ring off the wall.

Why? We know perfectly well that no virus, no bacterium, no chemical or other environmental agent has ever been flagged as the culprit. Yet, when we hear news of an inordinate number of cases in one geographic area, suddenly the possibilities of infection or contagion come alive. The public reacts. And epidemiologists, who study the spread of the disease, are alerted.

Several steps are necessary for determining if a multiple sclerosis "cluster" is legitimate. Epidemiologists note that often some patients in a reported cluster do not have multiple sclerosis at all. Experts therefore recommend that reported patients be carefully examined by neurologists. Once a diagnosis is confirmed in a given patient, it must then be determined whether multiple sclerosis occurred after the patient became a resident of the place in question. It is also important to ascertain where the patient lived during his childhood, because multiple sclerosis appears to be linked to the location in which people spend the first 15 years of their lives, even though clinical manifestations may surface much later.

One of the earliest and most famous clusters known to MS investigators was an "epidemic" that occurred on the Faroe Islands, a Danish possession lying in the north Atlantic between Norway and Iceland. Though the inhabitants are Nordic and considered a high-risk group for the disease, there are no known reports of MS among native-born residents before 1943.

In the early 1960s a Washington, D.C. neurologist, Dr. John Kurtzke, became intrigued with a report by a Danish investigator, K. Hyllested, about 29 cases of MS in the Faroes that had occurred starting in 1943. "This looked like a real epidemic," he said. "Obviously, the disease had to have been brought into the Faroes since it hadn't been there before."

The only thing brought into the Faroes in the 1940s was a battalion of British troops who occupied the islands as a protective measure during World War II. Assuming an incubation period of a few years, this would tally with an epidemic onset in 1943. The epidemic occurred only in people past puberty at the time of the British occupation. There was a second epidemic among those exposed as children, who developed multiple sclerosis only several years after puberty. In fact, a third, smaller wave of cases surfaced among those born after the British left. Many of the occupation soldiers were from the Scottish High-lands, where the MS prevalence is quite high: 90 cases per 100,000, comparable to rates in the northern U.S. In Dr. Kurtzke's view, if MS is somehow triggered by a virus, the disease may have been brought to the Faroese by the occupying forces.

A grantee of the Society since 1977 and author of the famous Kurtzke scale that delineates levels of disability, the neurologist is continuing a broad surveillance of new cases in the Faroes, scrutinizing areas in which no MS has been reported thus far, and analyzing results of 5,000 questionnaires sent out locally.

Clusters are usually first noticed by residents of a community, and Mansfield, Massachusetts was no exception. In 1971 a resident suggested that an unusually large number of people with multiple sclerosis had lived in the town from birth. This led to an investigation by a team working then at the University of Virginia School of Medicine.

Drs. Richard Eastman and the late David Poskanzer examined 17 patients and found 14 of them with probable or possible multiple sclerosis. This meant an MS prevalence rate of 141 per 100,000. The doctors carefully examined the histories of the patients but found no increase in childhood diseases or infectious illnesses among them. Eight patients had lived within several blocks of one another in the 1930s, and there was speculation that water contamination during that time might have been a factor in the MS cluster. But, the authors concluded it was not.

The next cluster to hit the headlines was in Saskatoon, in Saskatchewan, Canada, where a patient with multiple sclerosis, whose sister also had the disease and later died, insisted she had found a strikingly high prevalence of MS in and around the small community of Henribourg, 50 miles north of Saskatoon. She had identified 27 people who either had MS or had died affected with it. Based on the population, this was one person out of 11. Very high if, indeed, these were multiple sclerosis cases. Some could have been misdiagnosed.

Scientists at the University of Saskatchewan tried to review conditions as they had existed in Henribourg during and before World War II, when almost all the afflicted people were living in the village. Toxicologists examined local soil, water and base materials comparing them with samples from other areas. Their findings proved inconclusive.

An MS cluster that drew scare headlines was reported in Key West, Florida in 1985. A University of Miami physician, Dr. William Sheremata, announced he had found 23 cases of multiple sclerosis among the 26,000 residents of the island resort. Within a few months another five cases were uncovered, and Dr. Sheremata called in an expert to confirm that the patients really had MS. It appeared that most of the patients were natives of Key West. They hadn't migrated there, taking with them a "northern prevalence rate."