Neuromyasthenia and Chronic Fatigue Syndrome (CFS) in Northern Nevada/California: A Ten-Year Follow-Up of an Outbreak J of Chronic Fatigue Syndrome, Vol. 9(3/4) 2001, pp. 3-14 Paula S. Strickland, PhD, MPH; Paul H. Levine, MD; Daniel L. Peterson, MD; Karen O'Brien, BS; Thomas Fears, PhD 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:zpl@cu.nih.gov ). The authors are very grateful to George Reed, PhD, for his assistance in data analysis, and Deborah Pilkington for assistance in reviewing charts. ABSTRACT. 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%). KEYWORDS. Chronic fatigue syndrome, Nevada/California, neuromyasthemia, idiopathic chronic fatigue INTRODUCTION 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. Definitions: 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 months. 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 diagnosis. [Copies of the complete article are available for a fee from The Haworth Document Delivery Service: 1-800-342-9678. E-mail address: mailto:getinfo@haworthpressinc.com Website: http://www.HaworthPress.com ] © 2001 by The Haworth Press, Inc. All rights reserved.