MRC Social, Genetic, Developmental Psychiatric Research Centre, Institute of Psychiatry, London
Department of Psychological Medicine, University of Wales College of Medicine, Cardiff
Correspondence: Professor Anne Farmer, MRC Social, Genetic, Developmental Psychiatric Research Centre, Institute of Psychiatry, De Crespigny Park, Camberwell, London SE5 8AF, UK. Tel: +44 (0) 207 848 0940; fax: +44 (0) 207 848 0856; e-mail: spjuaef{at}iop.kcl.ac.uk
Declaration of interest Funded by a grant from the PPP Charitable Trust (A.F. and A.T.).
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ABSTRACT |
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Aims To estimate the lifetime prevalence of different definitions of chronic fatigue in 8- to 17-year-olds.
Method Participants came from two population-based twin series. Parents completed self-report questionnaires that enquired whether either child had ever experienced more than a few days of disabling fatigue. Telephone interviews were undertaken for individuals who had experienced such an episode.
Results Questionnaires were returned by 1468 families (65% response rate) and telephone interviews were undertaken regarding 99 of the 129 subjects (77%) who had experienced fatigue. The lifetime prevalence estimates ranged from 2.34% (95% CI 1.752.94) for disabling fatigue lasting 3 months to 1.29% (95% CI 0.871.71) for a disorder resembling adult operationally defined chronic fatigue syndrome.
Conclusions From the age of 11 years, young people have similar rates and types of chronic fatiguing illnesses to adults.
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INTRODUCTION |
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METHOD |
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The combined registers consisted of 3051 pairs of twins aged 817 years. The general practitioners of all the twins were first contacted to check for any contra-indications to contact by the study team, which led to 34 families not being approached. A further 748 families could not be located at the address listed on the register and further efforts to verify the current address held by a British Telecom database or the electoral register proved unsuccessful. Consequently, the final sample consisted of 2269 twin pairs, of whom 29.8% came from South Wales and 70.2% from Manchester.
Measures
The parents were sent questionnaires relating to each child separately, to
complete and return by post. Three reminder letters and a further set of
questionnaires were sent to non-responders 4 months after the first
mailing.
The questionnaires enquired whether the child had ever experienced a period of tiredness lasting at least several days that had caused interference with activities such as being able to go to school or see friends or family. If they answered yes to this question, they were asked to indicate the duration of the disabling fatigue on a five-point scale, ranging from a few days to more than 6 months. Parents were also asked to give written consent to further contact by telephone.
Those who agreed to further contact and where one or both children had experienced more than a few days of fatigue were interviewed by telephone. For those over the age of 11 years, both the main carer and the young person were interviewed. For younger participants, only the parent/main carer was interviewed. In this study we report on the results of the parents interviews.
The interview consisted of two parts. The first part obtained further details about the period(s) of fatigue, including the type and degree of impairment in functioning as well as information to determine whether the young person had experienced a similar symptom profile, duration and impairment to the Centers for Disease Control operational criteria for CFS in adults (Fukuda et al, 1994). The second part of the interview consisted of the depression section of the Child and Adolescent Psychiatric Assessment (Angold & Costello, 1995).
Information was sought about the duration of the fatigue and whether it had been continuous or episodic. The nature and degree of impairment associated with the fatigue was assessed by enquiring about whether the twin needed to rest for at least 1 hour daily, whether there was interference with school attendance, and how the tiredness interfered with the subjects usual activities and family and peer relationships. With regard to school attendance, the parent was asked whether the twin needed to take time off from school and whether the amount of time off from school meant that the twin had to repeat a school year, catch up in the school holidays, have a home tutor, have work sent home by teachers or have a reduced timetable. Parents were also asked about the number of visits to general practitioners and/or hospital specialists made regarding the fatigue. The interviewer also recorded verbatim the diagnoses that the parent reported had been made by the general practitioner and/or hospital specialist. The physician diagnoses were reviewed by an independent clinician who determined those cases where the diagnosis could entirely explain the chronic fatigue in the twin. These cases were then excluded from further analysis. In addition, the parent was also asked what he or she thought was the cause of the fatigue. These responses were also recorded verbatim.
To assess whether the young persons fatigue resembled that found in adults and fulfilled the adult Centers for Disease Control criteria for CFS (Fukuda et al, 1994), enquiry was made about symptoms that sometimes occur with fatigue. These were lack of energy, need for rest, unrefreshing sleep, muscle pain, eye strain, poor memory and concentration, slips of the tongue, difficulty in initiating activities, fatiguability, headaches, multiple joint pains, tender lymph nodes, feeling weak, sore throats, difficulty thinking or post-exertion malaise associated with the period of fatigue. These items were rated as less than usual, same as usual, more than usual or a lot more than usual for the episode of chronic fatigue.
The second part of the telephone interview consisted of the depression section of the Child and Adolescent Psychiatric Assessment (Angold & Costello, 1995), a semi-structured investigator-based research diagnostic interview. The responses to this were used to apply the DSMIV (American Psychiatric Association, 1994) operational criteria for major depression for the episode of fatigue.
Analyses
The population-based twin pairs can be considered as independently sampled,
but each pair contributes two sets of observations that cannot be classed as
independent (Bland & Kerry,
1997). Consequently, the survey analysis procedures of Stata
Release 6 for PC were used to adjust the variances of the analyses, which were
used in versions of independent t-tests and 2
tests.
Because not all families where there were positive replies to the screening fatigue questions wished to be interviewed, a mid-range estimate of prevalence was calculated that assumed that the same proportion of children fulfilled the different definitions of chronic fatigue in those from families who did not agree to participate as among those who did.
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RESULTS |
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One hundred and twenty-nine young people (4.4%) were identified by the screening questionnaires as having experienced more than a few days of disabling fatigue, and telephone interviews were undertaken for 99 (77%). Of those not interviewed, 15 had indicated that they did not wish to participate and a further 15 failed to respond to written requests for telephone contact. Following the interview, three young people who had diagnoses of cerebral palsy, nephrotic syndrome and thalassaemia were also excluded following independent paediatric advice that these disorders could entirely explain the fatigue. Thus, the following results are based on 96 young people (see Fig. 1).
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Age at interview, gender and location
For 12 families both twins were reported as having experienced disabling
fatigue, whereas for 72 families only one twin was reported as having
experienced disabling fatigue. Thirty-one (32%) of the twins came from South
Wales whereas 65 (68%) came from Greater Manchester. Two-thirds (64) of the
fatigued twins were female and one-third (32) were male. The mean age at
interview was 14 years 8 months (range: 9 years 5 months to 18 years 5
months).
Characteristics of fatigue
The mean age of onset of fatigue in the 32 boys was 11 years 1 month
(s.e.=7.93 months) and for the 64 girls it was 11 years 3 months (s.e.=6.23
months). There were no significant gender differences for age at onset.
The mean duration of fatigue in the 32 boys was 9.18 months (s.e.=5.15) and for the 64 girls it was 13.84 months (s.e.=3.51). There were no significant gender differences for duration of fatigue.
Other symptoms associated with prolonged fatigue
Table 1 shows that the most
common associated symptoms were lacking energy, needing to rest, multiple
joint pain and unrefreshing sleep. The Centers for Disease Control criteria
for CFS in adults (Fukuda et al,
1994) require the presence of at least four out of eight minor
symptoms concomitant with the period of fatigue (these eight symptoms are
indicated by asterisks in Table
1). A total of 86% of boys and 77% of girls had at least four
concomitant symptoms.
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Educational and social impairment
A total of 14 boys (44%) and 34 girls (53%) had to have time off from
school because of the fatigue and for 9 boys (28%) and 24 girls (38%) this
interference with their education was more severe, requiring extra work in the
holidays, work sent home by teachers, a home tutor or a reduced timetable.
Boys missed a mean of 9.50 days (s.e.=2.22) and girls missed a mean of 14.62
days (s.e.=1.97) per term. Parents of all 96 subjects reported that chronic
fatigue had caused impaired relationships with family and friends and reduced
participation in leisure activities.
Visits to doctors
General practitioners were consulted about the fatigue for 22 boys (67%)
and 44 girls (67%). For 12 (36%) boys and 24 (36%) girls a hospital specialist
opinion was also sought. For the boys, the mean number of visits to the
general practitioner was 2 (s.e.=0.26) and for girls it was 4.35 (s.e.=0.75).
Girls had significantly more visits to their general practitioners compared
with boys (t=-2.96, d.f.=64, P=0.005). In 22 cases general
practitioners considered that the tiredness was due to some type of infection,
including glandular fever (five cases), but in 21 cases they failed to give an
explanation for the fatigue according to the interviewed parent. Psychological
causes, age, hormones or puberty were given as causes of the fatigue in nine
subjects whereas single causes were given for the remainder. Hospital
specialists were more likely to have given a diagnosis for the cause of the
fatigue and there was uncertainty only in five cases. Psychological or
psychiatric causes were given in five cases and specific infections in four.
The general practitioners and specialists were reported to have carried out 42
blood tests, of which eight had positive findings (four indicated an infection
and four indicated anaemia). Only in one case was a diagnosis of CFS made by a
hospital specialist (a full table of the diagnoses given and tests undertaken
by general practitioners and hospital specialists can be obtained from the
authors on request). The commonest parental attribution for fatigue in their
twin was a psychological cause (28% of fatigued twins) whereas a further 20%
of parents thought that their twins fatigue was due to an infection.
Chronic fatigue syndrome or myalgic encephalomyelitis was not attributed as a
cause by any parent (a full table of all the causes cited by parents for
fatigue in the twins can be obtained from the authors on request).
Depression and chronic fatigue
Twelve boys (38%) and 25 girls (39%) fulfilled the DSMIV operational
definitions for mild, moderate or severe depression during the episode of
fatigue. There were no gender differences for concomitant depression.
Table 2 shows that the
percentage of subjects with co-occurring depression rises as the duration and
severity of the fatigue increases.
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Numbers of subjects fulfilling different definitions of chronic fatigue and CFS
Table 2 shows that of the 32
boys and 64 girls with more than a few days of chronic fatigue, for 19 boys
and 50 girls this lasted for at least 1 month. For 17 boys (53%) and 44 girls
(67%) the chronic fatigue had lasted at least 3 months, of whom 14 boys (44%)
and 36 girls (55%) had also had at least four concomitant symptoms. Nine boys
(28%) and 26 girls (41%) experienced fatigue lasting 6 months with at least
four concomitant symptoms. There were no gender differences for these
different severities of fatigue. Table
2 also shows that the mean ages of onset for these different
durations of fatigue ranged from 11.13 years to 12.43 years, and that between
one-third and a half of the subjects also fulfilled DSMIV criteria for
depression during the period of chronic fatigue.
Prevalence of different definitions of chronic fatigue
The estimated prevalence of fatiguing illness lasting 3 months or more was
2.34% (95% CI 1.752.94) whereas the prevalence of fatigue lasting 3
months accompanied by at least four minor symptoms from the Centers for
Disease Control criteria for CFS was 1.90% (95% CI 1.402.40). Lastly,
the prevalence of 6 months or more of fatigue with at least four minor
symptoms was 1.29% (95% CI 0.871.71).
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DISCUSSION |
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Frequency, duration and age of onset of chronic disabling fatigue in young people
The results show that disabling fatigue in young people is not rare and
that 4.4% of the parents who responded to a questionnaire survey reported the
symptom lasting for more than a few days in one or both of their children.
However, this is less than half the rate in adults where estimates for the
rates of persistent fatigue complaints to primary care
physicians range from 11% to 27% (Wessely
et al, 1997;
Skapinakis et al,
2000; Sharpe & Wilks,
2002). The study showed that the mean duration of chronic fatigue
(9.57 months for boys and 13.49 months for girls) is similar to that reported
in studies of CFS in paediatric clinic samples. For example, Carter et
al (1995) report a mean
duration of 11 months in 20 individuals whose mean age was 13 years, whereas
Feder et al (1994)
report a mean duration of 7 months in 48 young people whose mean age was 15
years. However, the individuals in the present study were younger than these
specialist clinic referrals, with the mean age at onset for both genders
around 11 years. This is very similar to that reported in a telephone survey
of CFS-like illnesses in children in Chicago where the mean age at onset was
11.6 years (Jordan et al,
2000). Thus, community surveys such as the present study appear to
identify fatiguing illness of the same duration as those reported from
specialist clinical services, although the children are on average at least 2
years younger.
Our study confirms the findings from other studies that chronic fatigue is rare in children under 10 years old (Marshall, 1999). In addition, the gender ratio of approximately twice as many girls (67%) as boys (33%) reported with the symptom is also similar to other studies both of children and of adults (Carter et al, 1995; Wessely et al, 1997).
Relationship of chronic fatigue in the twins to operationally defined CFS
Following the telephone interview we have found that chronic fatigue of the
same duration, impairment and number of associated symptoms as the adult
Centers for Disease Control operational definition of CFS
(Fukuda et al, 1994)
has an estimated lifetime prevalence of 1.29%, whereas for a broader
definition, including those with 3 months of symptom duration, a lifetime
prevalence of 1.90% was found. The prevalence estimates for these
broad (3 months duration) and narrow (6
months duration) definitions of chronic fatigue are not much different,
which supports the view that the diagnosis of CFS in this younger age group
should be made after 3 months of symptoms with impairment rather than after 6
months as the adult definition requires
(Royal Colleges of Physicians,
Psychiatrists and General Practitioners, 1996).
Despite not being formally diagnosed with CFS, the gender ratio (twice as many girls as boys), number and type of associated symptoms, frequency of co-occurring depression (just under 40%) and duration and impairment of chronic fatigue are little different in our population-based sample compared with those reported for clinical samples of young people diagnosed with CFS (Feder et al, 1994; Carter et al, 1995; Garralda & Rangel, 2001). It is also noteworthy that the percentage of subjects with co-occurring depressive disorder also increased with increasing duration of their chronic disabling fatigue.
Comparisons with another recently published epidemiological study of chronic fatigue in young people
Our prevalence estimates based on parental accounts are somewhat higher
than the rates reported by Chalder and colleagues who undertook telephone
interviews with 4240 children aged 1115 years as part of a large
epidemiological study of mental health in this age group
(Chalder et al, 2003).
They report a chronic fatigue prevalence of 0.57% (95% CI 0.340.80)
whereas we have a narrow definition prevalence of 1.29% (95% CI
0.871.71). However, from the published account of their study it would
appear that they have determined point prevalence whereas in our study we have
presented lifetime prevalence estimates.
Limitations of the study
Our study has a number of limitations. First, the results are based on an
interview with a parent and not the child. Second, the interviewer was not a
clinician so medical exclusions were based on obtaining a verbatim account of
what the parent reported a doctor had said was the cause of fatigue in the
twin and the advice of an independent clinician that the medical condition
listed could entirely explain the chronic fatigue. Other conditions that could
have partly explained the fatigue (e.g. viral infections) but not its severity
or duration were retained in the analyses. Finally, because of the absence of
a clinical examination of the twins, we have only reported on the resemblance
of our subjects to CFS as defined by the Centers for Disease Control in terms
of morbidity rather than the subjects fulfilling these criteria. Despite these
caveats, our study has shown that the symptom pattern and severity, duration
and associated impairment associated with chronic fatigue in young people are
similar to those found in studies of adults with CFS
(Farmer et al, 1996;
Wessely et al, 1997)
and that prevalence estimates also fall within the range of 0.072.6%
reported in studies of chronic fatigue in adults
(Bates et al, 1993;
Buchwald et al, 1995; Wessely et al,
1997).
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Clinical Implications and Limitations |
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LIMITATIONS
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Received for publication August 14, 2003. Revision received January 23, 2004. Accepted for publication February 1, 2004.
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