Article: The Definition Of Disabling Fatigue In Children
Article: The definition of disabling fatigue in children and adolescents
9 August 2005
BMC Fam Pract. 2005; 6: 33.
Published online 2005 August 9. doi: 10.1186/1471-2296-6-33.
Copyright © 2005 Fowler et al; licensee BioMed Central Ltd.
Tom Fowler , Pamela Duthie , Anita Thapar , and Anne Farmer
 Department of Psychological Medicine, Wales College of Medicine,
Cardiff University, UK
 Brynffynnon Child & Family Service Unit, Pontypridd, UK
 MRC Social, Genetic, Developmental Psychiatric Research Centre,
Institute of Psychiatry, London, UK
Tom Fowler: firstname.lastname@example.org; Pamela Duthie: email@example.com;
Anita Thapar: firstname.lastname@example.org; Anne Farmer: email@example.com
Received February 14, 2005; Accepted August 9, 2005.
Disabling fatigue is the main illness related reason for prolonged
absence from school. Although there are accepted criteria for diagnosing
chronic fatigue in adults, it remains uncertain as to how best to
define disabling fatigue and Chronic Fatigue Syndrome (CFS) in children
and adolescents. In this population-based study, the aim was to
identify children who had experienced an episode of disabling fatigue
and examine the clinical and demographic differences between those
individuals who fulfilled a narrow definition of disabling fatigue
and those who fulfilled broader definitions of disabling fatigue.
Participants (aged 8-17 years) were identified from a population-based
twin register. Parent report was used to identify children who had
ever experienced a period of disabling fatigue. Standardised telephone
interviews were then conducted with the parents of these affected
children. Data on clinical and demographic characteristics, including
age of onset, gender, days per week affected, hours per day spent
resting, absence from school, comorbidity with depression and a
global measure of impairment due to the fatigue, were examined.
A narrow definition was defined as a minimum of 6 months disabling
fatigue plus at least 4 associated symptoms, which is comparable
to the operational criteria for CFS in adults. Broader definitions
included those with at least 3 months of disabling fatigue and 4
or more of the associated symptoms and those with simply a minimum
of 3 months of disabling fatigue. Groups were mutually exclusive.
Questionnaires were returned by 1468 families (65% response rate)
and telephone interviews were completed on 99 of the 129 participants
(77%) who had experienced fatigue. There were no significant differences
in demographic and clinical characteristics or levels of impairment
between those who fulfilled the narrower definition and those who
fulfilled the broader definitions. The only exception was the reported
number of days per week that the child was affected by the fatigue.
All groups demonstrated evidence of substantial impairment associated
with the fatigue.
Children and adolescents who do not fulfil the current narrow definition
of CFS but do suffer from disabling fatigue show comparable and
substantial impairment. In primary care settings, a broader definition
of disabling fatigue would improve the identification of impaired
children and adolescents who require support.
Disabling fatigue in children and adolescents is an important clinical
problem given that it is associated with severe functional impairment
that has an impact upon the child's education and social development
[1,2]. It is the main illness related reason for prolonged absence
from school in young people . It is also a presenting problem
for 2% and a background problem in 11% of school children attending
general paediatric clinics . There is uncertainty about how to
appropriately define disabling fatigue in children and adolescents.
Reviews of disabling fatigue in children and adolescents highlight
the lack of research in this age group in comparison to adults .
There have been several attempts to define disabling fatigue as
a disorder in adults and perhaps the most accepted is the Center
for Disease Control (CDC) definition . This requires 6 months
of disabling fatigue and 4 or more of the following symptoms; 1)
impaired memory or concentration, 2) sore throat, 3) tender cervical
axillary lymph nodes, 4) muscle pain, 5) multi-joint pain, 6) new
headaches, 7) unrefreshing sleep, 8) post-exertion malaise. This
has, to date, been the most widely used definition when reporting
the prevalence of CFS and CFS like illness in children and adolescents
A number of authors have raised the concern that the current criteria
for CFS were designed for use in adults and that there has been
relatively little work in assessing how appropriate these criteria
are for children and adolescents [10-14]. Although a consensus document
on CFS by the Royal Colleges  suggested that the criteria were
applicable to children and adolescents it did also suggest the period
of disabling fatigue required for a diagnosis of CFS should be reduced
from 6 to 3 months.
The importance that these associated symptoms play in CFS and whether
they contribute to defining a homogenous group of individuals with
disabling fatigue has been increasingly questioned . As the
associated symptoms were originally identified by expert consensus
there are growing calls for studies examining individuals with chronic
unexplained fatigue to empirically derive a definition of CFS .
Given the current discussion about the role of the associated symptoms
in CFS in adults, the lack of empirical testing about the appropriateness
of the adult CFS criteria in children it seems pertinent to examine
whether the clinical and demographic features of children and adolescents
differ in those who fulfil CFS criteria and those who fulfil broader
criteria for disabling fatigue. Evidence that those individuals
with "adult like CFS" did differ significantly would give
credence to the idea that adult CFS criteria do identify a specific
group of fatigued individuals.
There is also evidence to suggest that the majority (two thirds)
of adults who attend GP clinics regarding disabling fatigue lasting
more then 6 months do not fulfil the CDC definition of CFS, but
do have substantial associated impairment . Given this it is
also important to examine and compare the levels of impairment in
children and adolescents who fulfil CFS criteria and those who fulfil
broader definitions of disabling fatigue. The latter may represent
an important group of individuals who require treatment and primary
In this paper, we set out to identify children and adolescents
with a lifetime ever episode of disabling fatigue in a population-based
sample and test whether those who fulfilled a narrow definition
were more severely impaired and different in terms of clinical and
demographic characteristics than those who only fulfilled broader
definitions of chronic disabling fatigue. Specifically, three groups
of individuals with disabling fatigue were defined; those who had
a similar symptom profile, duration and impairment as the CDC operational
criteria for CFS in adults ("adult like CFS"), those who
also had a similar symptom profile and impairment but whose fatigue,
at time of interview, had lasted for a period of between 3-6 months
disabling fatigue ("child like CFS") and those that did
not fulfil the symptom profile for operationally defined CFS but
who had had more than 3 months disabling fatigue ("3 months
plus disabling fatigue").
Participants were identified from the population based twin register
CaStANET (Cardiff Study of All Wales and North West England Twins).
Previous studies have shown that the register is representative
of the local population . Initially 2259 twin pairs aged between
8-17 years old were identified from the register and a questionnaire
package was sent to these twins and their parents. Families in which
the parents reported that a child had experienced a period of disabling
fatigue which had lasted for more than a few days and had caused
interference with activities such as being able to go to school,
or see friends or family, were selected for a standardised parental
telephone interview. Ethical approval was granted by the Multi-Centre
Research Ethics Committee (MREC) for Wales.
The parental telephone interview is described in detail elsewhere
. The interview consisted of two parts. The first part obtained
further details about the period(s) of fatigue.
To assess whether the young person's fatigue could be classified
as "adult like CFS", "child like CFS" or "3
months plus disabling fatigue" enquiry was made about the associated
symptoms that sometimes occur with fatigue . These were poor
memory and concentration, difficulty thinking, sore throats, tender
lymph nodes, muscle pain, multiple joint pains, headaches, unrefreshing
sleep, fatigubility, or post-exertion malaise associated with the
period of fatigue. Items were rated as 'less than usual', 'same
as usual', 'more than usual' or 'a lot more than usual' for the
episode of fatigue. Those children whose parents reported "more
than usual" or "a lot more than usual" for 4 or more
of the associated symptoms required by the CDC definition of CFS
in adults were classed as fulfilling the associated symptom requirement.
Questions were also asked about the duration of the fatigue, whether
it was ongoing at the time of interview and whether it had been
continuous or episodic (where the periods of fatigue were described
as episodic the parent was asked to focus on the longest most debilitating
period of fatigue for the remainder of the questions). The duration
of the fatigue at the time of interview was used to classify the
twins into the different categories regardless of whether the fatigue
was currently ongoing. 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, and whether there was
interference with school attendance, and/or usual leisure activities
and with family and peer relationships. To be classed as suffering
from "disabling fatigue" the twin was required to need
to rest for at least 1 hr daily and for there to be a report of
some interference in at least one of these areas.
Individuals who did not fulfil the associated symptom requirement
but had experienced a period of disabling fatigue of greater than
3 months at the time of interview were classed as suffering from
"three months plus disabling fatigue". Those who did fulfil
the associated symptom requirement but had only experienced a period
of between 3-6 months of the disabling fatigue at the time of interview
were classed as suffering from "child like CFS" and those
who has experienced a period of more than 6 months disabling fatigue
were classed as suffering from "adult like CFS"
Information was also sought about the age of onset of the fatigue,
the number of days per week affected by the fatigue, the number
of hours per day that the affected child required to rest/sleep,
whether the child or adolescent was absent from school due to the
fatigue, and whether they were taken to visit a General Practioner
with regard to the fatigue. A global measure of impairment was created
by asking whether the fatigue had interfered with the following
4 areas; i) the child's schoolwork, ii) peer relations, iii) family
relations and iv) their usual leisure pursuits. The possible response's
to these questions were on a discrete adjective scale consisting
of "Not much", "A little" or "A lot"
and were scored as 0, 1, or 2 respectively. The answers to these
questions were then summed to give the overall score which ranged
from 0 to 8.
Parents were asked whether any diagnoses or explanation for the
disabling fatigue had been offered by GP's or hospital specialists,
when these had been visited. Their responses were recorded verbatim.
This information was then reviewed by one of the authors (PD) who
was blind to other information from the data collection and who
determined those cases where the diagnosis could entirely explain
the chronic fatigue in the twin. These cases were then excluded
from further analysis.
The second part of the interview consisted of the depression section
of the parent version Child and Adolescent Psychiatric Assessment
(CAPA) . This is a standardised, reliable psychiatric interview
that assesses psychopathology in children and adolescents. The responses
to this were used to generate DSM-IV defined diagnoses of major
depression during the episode of fatigue.
As it was determined that the most important analysis to undertake
was to assess whether those individuals who fulfilled just the broad
definitions of disabling fatigue ("child like CFS" and
"3 months plus disabling fatigue") differed from those
who fulfilled the narrow definition ("adult like CFS")
and to reduce multiple testing no comparisons were made between
individual classed as suffering from "child like CFS"
and those who had "3 months plus disabling fatigue". Two
sets of comparisons were therefore made, the first between those
individuals who had "adult like CFS" and those who had
"child like CFS", the second between those individuals
who had "adult like CFS" and "3 months plus disabling
fatigue". Independent t-tests and chi-square tests were used
However, although the twin register is population based, each twin
pair could potentially contributes two observations, and where this
is the case the individual twin cannot be classed as statistically
independent. Reduced variance due to the correlation between twins'
scores can cause high false positive rates . To adjust for this
bias the data was treated as equivalent to a 2-stage cluster design
with the twin pairs as the primary sampling unit . Consequently,
the survey analysis procedures of the statistical analysis package
STATA Release 6  were used to adjust the variances of all analyses
to be equivalent to independently sampled pairs. Each family unit
was classed as a clustering unit, with some clusters containing
information from both twins, while others contained information
from just one.
Parents from 1468 families returned questionnaires (65% response
rate). There were no significant socio-demographic differences between
the responding and non-responding families . The screening questionnaire
identified one hundred and twenty nine children and adolescents
who had experienced more than a few days of disabling fatigue and
telephone interviews were undertaken on 99 (77%). For the remaining
individuals parents had either not given permission to be contacted
for a telephone interview when returning the questionnaires or when
contacted did not wish to take part. Of the families who met the
selection critieria there were 11 twin pairs where interviews were
conducted about both twins. Following the interview, 3 participants
whose parents reported diagnoses of Cerebral Palsy, Nephrotic Syndrome
and Thalassaemia, were excluded from the analysis as it was felt
that these disorders could entirely explain the presence of the
Twins classed as suffering from "3 months plus disabling fatigue"
had an average duration of fatigue of 25.8 months (standard error
of mean, SEM, 14.0) of which 27% still had ongoing fatigue at the
time of interview. Twins classed as suffering from "adult like
CFS" had an average duration of 23.5 months of fatigue (SEM
6.1) with 41% with ongoing fatigue at the time of interview. Those
classed as suffering "child like CFS" had by definition
between 3-6 months disabling fatigue, of which 27% had ongoing fatigue
at the time of interview. Table 1 shows the male: female ratio,
age of onset, days per week impaired during the worst period of
fatigue, hours per day impaired by the fatigue, number of days absent
from school per term during the worst period of fatigue and the
global impairment score. It also presents the percentage in each
group who visited a GP with regard to the fatigue and who fulfilled
DSM-1V criteria for depression during the period of fatigue.
The results of the statistical analysis suggested no significant
difference (P > 0.1) between the groups. The only exception to
this was the number of days that the child was affected during the
episode of fatigue, for which there is a significant difference
between individuals who were classed as suffering from "adult
like CFS" and those classed as suffering from "child like
CFS" (t = -2.58, df 47, p = 0.027). These analyses were repeated
using non-parametric tests, however there was no difference in results.
The descriptive statistics suggested that there was greater variability
in individuals classed as suffering from "3 months plus disabling
fatigue" than in individuals in the other two groups, particularly
for the age of onset and number days per term absent from school.
Less individuals from this group had visited a GP with regard to
the fatigue. Although no significant differences or trends were
found between individuals classed as suffering from "3 months
plus disabling fatigue" and those classed as suffering from
"adult like CFS" for these 3 variables, because of the
descriptive statistics, a post hoc set of analyses was also conducted.
For the post hoc analyses individuals classed as suffering from
"adult like CFS" and "child like CFS" (i.e.
all those individuals who had more than 3 months disabling fatigue
and whose symptom profile resembled that of the CDC operational
criteria for CFS) were combined into one group and compared to those
classed as suffering from "3 months plus disabling fatigue".
However no significant differences were found between these groups
for age of onset, number of days absent from school per term or
visits to the GP. As in the previous statistical analyses, these
tests were also repeated using non-parametric tests however there
was no difference in the pattern of results.
The results indicate that the clinical and demographic characteristics
and level of impairment of children with narrowly defined disabling
fatigue and more broadly defined fatigue are similar. There was
no significant difference in gender ratio, the average age of onset
or the rate of comorbidity with depression between the groups. Likewise
affected young people seemed to spend a similar number of hours
resting and/or sleeping, there was parental report of similar levels
of global impairment, they were absent for a similar number of days
from school during the term in which they were most affected by
the fatigue and a similar percentage of individuals were contacting
their GP about the fatigue.
A lack of significant findings cannot necessarily be interpreted
as meaning there is no differences between these groups but there
are still a number of implications of these results. Specifically,
the results suggest that a longer duration of fatigue and accompanying
symptoms are not necessary in defining disabling, impairing fatigue
in children and adolescents. Children who present with shorter histories
of fatigue and/or in the absence of CFS associated symptoms have
high levels of parent reported impairment, both in terms of family
and peer relationships and school work. They also appear to be absent
for a substantial number of days from school and it causes enough
worry for the parents to take the majority of these children and
adolescents to a GP. Even though their was a significant difference
for the number of days affected by the disabling fatigue between
those individuals classed as suffering from "adult like CFS"
and "child like CFS", all groups reported that they were
affected by the disabling fatigue for most days of the week.
The descriptive statistics also suggested the possibility that
individuals within the "three months plus disabling fatigue
group" may be more heterogeneous, given that there is a relatively
large amount of variance in this group in comparison to the other
groups. Although this may have nosological implications it does
not negate the high level of impairment this group also appears
to be experiencing.
One important limitation of this study is that the individual's
symptoms were identified by telephone interview rather than medical
examination. Although every effort was made to exclude individuals
who may have had an alternative diagnosis that would explain the
fatigue this does not guarantee that if an in depth medical assessment
were undertaken with these individuals that a number would not be
classed as fulfilling the CDC definition of CFS. This may in some
way explain why over half individuals in this population based sample
showed a similar symptom profile to the CDC criteria for CFS whereas
in the adult population only one third were categorised as fulfilling
this criteria , although this may also be due to differences
in presentation and/or aetiology of disabling fatigue between adults
and children and adolescents. However this does not change the fact
that all these individuals are reporting high levels of impairment
and interference with their life due to the fatigue.
A further possible limitation is that parent report of disabling
fatigue was used to identify individuals for further data collection
and the analysis is based on information from parental interview
only. There are often low levels of agreement between parent and
child/adolescent report of behavioural/psychiatric symptoms 
and there is some evidence that this is also the case with CFS symptoms
. However as life time ever disabling fatigue was being examined
and as there is evidence that adolescents and young adults may often
not recall key symptoms (for example, over 50% of individuals with
a diagnosis of depression between 15-21 failed to recall a key symptom
at age 25 ) it seemed most appropriate to use parent report.
Further interviews with twins over the age of 12 were also conducted
and on prompting 97% were able to recall a period of disabling fatigue
about which it was possible to conduct the interview.
These findings have clinical significance in that they imply episodes
of fatigue in children and adolescents which last at least 3 months
warrant investigation regardless of whether or not a diagnosis of
CFS can be made. This is because the degree of impairment is substantial
in terms of interference with usual activities, family and peer
relationships, school absence and school work, and the impairment
does not appear to differ from the level of impairment found in
more narrowly defined disabling fatigue.
There was no indication that the group of children with shorter
periods of fatigue differed on a number of associated characteristics
(in terms of gender ratio, comorbidity with depression and age of
onset) or in terms of impairment from the group of children who
had a symptom profile similar to the CDC criteria for CFS. Although
this does not prove that there is no differences between individuals
in these groups it does indicate that within a primary care setting
it may be appropriate to consider a broader definition of disabling
fatigue in children for clinical and research purposes.
The author(s) declare that they have no competing interests.
TF interviewed the families, performed the statistical analysis
and drafted the manuscript. PM provided clinical advice when conducting
the analysis and helped drafted the manuscript. AT participated
in the design and coordination of the study. AF conceived of the
study, and participated in its design and coordination.
The pre-publication history for this paper can be accessed here.
Funded by a grant from PPP Charitable Trust (AF & AT).
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Figure And Tables
1: Characteristics of individuals who fulfil different duration
and associated symptom criteria of disabling fatigue
Source: BMC Fam Pract. 2005; 6: 33. [Published
online 2005 August 9. doi: 10.1186/1471-2296-6-33.]
Category: The definition of disabling fatigue
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