Neuromyasthenia and Chronic Fatigue Syndrome : A Ten-Year Follow-Up
By Paula S. Strickland, Ph.D., M.P.H.; Paul H. Levine, M.D.; Daniel L. Peterson, M.D., Karen O' Brien, B.S., Thomas Frears, Ph.D. •
November 28, 2001
Neuromyasthenia and Chronic Fatigue Syndrome in Northern Nevada/California: A Ten-Year Follow-Up of an Outbreak
Journal: J of Chronic Fatigue Syndrome, Vol. 9(3/4) 2001, pp. 3-14
Author Affiliations: Paula S. Strickland is a former graduate student at George Washington University, School of Public Health and Health Services,
Washington, DC. Paul H. Levine is affiliated with the Viral Epidemiology Branch, National Cancer Institute, Bethesda, MD and George Washington University, School of Public Health and Health Services, Washington, DC. Daniel L. Petersen is Internal Medicine Physician, and Karen O'Brien is
Technician, Sierra Internal Medicine Associates, Incline Village, NV.
Thomas Fears is Statistician, National Cancer Institute, Bethesda, MD.
Address correspondence to: Paul H. Levine, MD, George Washington
University, School of Public Health and Health Services, Washington, DC
20037 (E-mail: mailto:firstname.lastname@example.org ).
The authors are very grateful to George Reed, Ph.D., for his assistance in
data analysis, and Deborah Pilkington for assistance in reviewing charts.
In 1984-87, an outbreak of debilitating fatigue was reported by two
physicians in the private practice of internal medicine in Incline
Village, Nevada. Follow-up questionnaires were sent in 1995 to the 259
patients in this outbreak. The results were analyzed to determine how
many patients met the latest Centers for Disease Control and Prevention
(CDC) case definition for Chronic Fatigue Syndrome (CFS), Idiopathic
Chronic Fatigue (ICF), or Prolonged Fatigue (PF). Data were analyzed
separately for those living in the Lake Tahoe area and those referred
from other locales. Of those returning questionnaires (123/259), 41 % met
the CDC case definition for CFS, 56% met the criteria for inclusion in
the subgroup ICF, and 3% experienced PF. In the population-based Lake
Tahoe group, symptomatic women were more likely to have CFS than ICF
whereas symptomatic men were likely to fit ICF criteria. Also in this
group, full recovery was reported more often among Lake Tahoe
participants classified as having ICF (43%) than participants classified
as having CFS (15%).
In 1984, two internal medicine practitioners noted an apparent outbreak
of fatiguing illness in Northern Nevada/California, which subsequently
became the subject of several reports (1-4). Although often referred to
as an outbreak of chronic fatigue syndrome (CFS), most of the studies
which evaluated 259 patients in this cluster between 1984 and 1987 were
carried out prior to the first published CFS working definition in 1988
(5), and it has not been clear what proportion of the patients who
suffered from the fatiguing illness actually had CFS. In a ten-year
follow-up to the study of Buchwald et al. (3), investigators involved
with the Incline Village private practice prepared a questionnaire that
was mailed in March 1995 to the 259 patients included in this report.
The questionnaire was initially designed to identify CFS patients based
on the case definition described by Holmes et al. in 1988 (5). However,
since this case definition does not provide a strategy for subgrouping
cases of chronic fatigue which are not CFS, the CFS definition and
chronic fatigue subgroups described by Fukuda et al. in 1994 (6) were
used in this report. Utilizing the questionnaire data our study had four
objectives: first, to summarize the questionnaire data using descriptive
information in order to determine what proportion of the affected
patients in the Northern Nevada/California cluster met the latest case
definition of CFS (6); second, to determine what proportion met the
criteria of the subgrouping described by Fukuda et al. (6); third, to
determine what proportion of the patients have recovered from their
illness after approximately ten years, and fourth, to determine if our
earlier data suggesting a relationship between this outbreak and the
subsequent increased incidence of brain tumors and non-Hodgkin's lymphoma
(7) would be confirmed in this cohort.
The CFS definitions and subgroups of chronic fatigue used to categorize
participants were based on the categories described by Fukuda et al. (6).
Chronic Fatigue Syndrome: Participants were classified as having CFS if
they experienced severe fatigue that persisted or relapsed for six months
or more, which was of new or definite onset; was not substantially
alleviated by rest, and resulted in substantial reduction in activities.
They also had to have four or more CFS associated symptoms (impaired
memory or concentration, sore throat, tender cervical or axillary lymph
nodes, muscle pain, multi-joint pain, new headaches, unrefreshing sleep,
and postexertional malaise). Finally, their illness could not be
attributed to any of a group of specific organic or psychiatric
conditions known to be associated with fatigue.
Idiopathic Chronic Fatigue: Participants were classified as having
Idiopathic Chronic Fatigue (ICF) if they experienced significant fatigue
which persisted for six months or longer, but the severity of fatigue or
the symptoms associated with fatigue did not meet the CFS definition.
Prolonged Fatigue: Participants were classified as having Prolonged
Fatigue (PF) if they experienced fatigue that was severe enough to seek
medical attention, but the duration of the fatigue was less than six
Patients were also characterized geographically to distinguish those in
the proximate area of the outbreak versus those subsequently referred
because of the interest of the physicians in chronic fatigue. The "Tahoe
group" is defined as those persons who were non-referral patients and
residents of the Lake Tahoe/Incline Village areas at the time of initial
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