during the last years an increased focus on fatigue symptoms / syndrome among children has been observed , together with an increase in referrals to our hospital . children with fatigue whether these illnesses are increasing in number or just an increase in referrals to the specialist , in part based on greater interest in the topic is unknown . the aetiology of the condition is still unclear after almost three decades of research in this area , where infectious , immunological , neuroendocrine , sleep , and psychiatric mechanisms , among others , have been investigated . despite the fact that no evidence has been found so far of an infectious aetiology , it has been proposed that a heterogeneous group of infections may trigger or maintain the symptoms of cfs . abnormalities in the immune system have been reported in cfs - patients , among these , deficiencies in natural killer cell function and increased expression of activation markers on the cell - surface of t - lymphocytes , especially increased numbers of cd8 + cytotoxic t cells that have certain antigenic markers . whether these abnormalities have any relationship to cfs and its symptoms remains unclear .   the prevalence of the condition among young adults in the twenties and older has been reported as three percent studies have found a higher prevalence of cfs of two to three among females [ 1 , 4 , 8 , 9 ] . found that children and adolescents with chronic fatigue have a syndrome that is similar to that described in adults but that the syndrome presents earlier in the course of the illness and has a more optimistic outcome . a doctoral thesis from norway did not find socioeconomic status to contribute to the fatigue symptom , opposite to what chalder et al . found . having a disabling condition like cfs in childhood and adolescence may pose major consequences regarding mental health , personal relationships , school attendance and participating in social life and work . it is important to ensure early and proper management of these patients [ 15 , 16 ] . the aim of the present hospital - based clinical retrospective study was ( 1 ) to estimate the number of children being diagnosed with g93.3 postviral fatigue syndrome during a 10-year period ( 2002 to 2011 ) and ( 2 ) describe the clinical and laboratory findings in children with postviral fatigue syndrome . the diagnosis given in icd-10 g93.3 postviral fatigue syndrome ( cfs ) is also used diagnosing children and adolescent with fatigue . however , time aspect with onset of symptoms is shorter for children than adults . all children and adolescents in the county where this study took place , was referred to specialist when diagnosing g93.3 post viral fatigue syndrome . all children suffering from fatigue are investigated in the department of paediatrics . during the first consultation the specialist will apply a preliminary diagnosis while the medical investigations are done . at the end of evaluation it should be noted that not all children with illness compatible with cfs will also fulfil criteria for postviral fatigue syndrome . the study was retrospective , and the subjects were all children under the age of 16 . a list of patients who underwent investigations and were diagnosed with g93.3 postviral fatigue syndrome according to the icd-10 classification was collected from the patient registry . the diagnosis was set by a paediatrician either during or at the end of the evaluation period . the following data were collected : ( 1 ) clinical examination , ( 2 ) blood sample tests , ( 3 ) other investigations , and ( 4 ) evaluation by physiotherapist , psychiatrist evaluating depression and anxiety using icd-10 criteria , and neuropsychologist assessing wisc - r measuring iq . body mass index ( bmi ) was calculated retrospectively based on weight and length as kg / m . we defined overweight as bmi > 25 and underweight as bmi < 17.5 . because some findings support the notion that cfs may be due to one or more immune disorders that have resulted from exposure to an infectious agent , igg antibodies to epstein - barr virus ( ebv ) and cytomegalovirus ( cmv ) were used as a measure of previous infection . a total number of 37 patients were referred with fatigue symptoms according to the patient registry . four patients were excluded due to obvious incorrect coding . of the remaining 33 , six ( 18% ) two were diagnosed with epilepsy , two with sleeping disorders , one with hypothyreosis and one did not fulfil the criteria of cfs or any other diagnosis . of the 27 who received the diagnosis g93.3 , four had comorbid chronic illness . there were an increased number of referred patients with fatigue during the 10-year period , with almost three in four patients investigated during the last three years ( 20092011 ) . previous studies have found that many children with cfs do have mental health problems irrespective of cause [ 2023 ] . according to the psychiatrist assessment , none of the patients suffered from anxiety or depression . three children had a pathological eeg ; two of them had epilepsy and one sleeping disorder . heart rate ( hr ) and blood pressure ( bp ) were all within normal range . one child had low ft4 and later diagnosed as hypothyreosis .   among the 27 patients referred with cfs , 16 ( 59% ) were boys . the mean average age for the onset of fatigue symptoms was 141 months ( sd 30 ) for boys and 136 months ( sd 31 ) for girls , respectively . being underweight , defined as bmi < 17.5 , was found in 12 ( 44% ) , while one ( 4% ) was overweight with a bmi > 25 . half of the underweight children were boys . of the 27 patients with cfs ( g93.3 ) , 20 ( 74% ) tested positive for igg to epstein - barr virus , six ( 22% ) tested positive for igg to cytomegalovirus , and one ( 4% ) tested positive to borrelia , indicating previous infection . in the present clinical retrospective study we found no gender differences among children and adolescent younger than 16 years of age with chronic fatigue symptom , with debut of symptoms after 10 years of age . almost half of them were underweight and half of these were boys . almost one in five suffering from fatigue symptoms proved to have other diagnoses . during the last decade , there have been an increase in number of referrals of children with fatigue as the only symptom . chronic fatigue syndrome is not a new syndrome , there are documented cases since the 19th century . however during the last decade , there has been an increased knowledge and awareness about the condition in the healthcare system and in the media in norway which influence the number of referrals .   in this study , the use of medical and biochemical test when assessing children and adolescence with chronic fatigue syndrome varied . the increased focus on the cfs diagnosis may have led to excessive use during the diagnostic evaluation process . the strength of the study is the retrospective design which allows us to confirm the diagnoses . in addition , due to uncertainty whether the whole county was covered , one can not estimate incidences . previous studies have reported a higher prevalence of cfs in the female population [ 25 , 26 ] . however , this was a very small population , and it is possible that the results could have been different in a larger group . time of onset seemed to be in accordance with other studies who describe symptom onset of fatigue between almost twelve until fifteen years . almost all patients reported themselves to be previously healthy prior to their fatigue and also ascribed the onset due to an infection . one in six had a chronic condition that could explain their fatigue symptoms but still fulfilling criteria for g93.3 postviral fatigue syndrome . the diagnosis of cfs is usually established after excluding other chronic conditions ; however , long standing medical or psychological conditions can also result in cfs . there is a gray area between fatigue due chronic medical and psychological conditions and fatigue which is a part of cfs . this zone needs to be examined carefully , and diagnostic criteria for cfs should be adjusted to clarify this overlap . interestingly , we found that more than one in three of the referred patients was underweight , with an equal gender representation . the question is whether the underweight as a cause of fatigue has been overlooked in the diagnostic process or the cfs itself is the reason for underweight . lack of the bmi records before the onset of fatigue symptoms makes it difficult to answer this question in our study . this is opposite to a recent study where high bmi was found to be significantly associated with prolonged duration of cfs in a retrospective cohort of children . many of the adolescents had additional symptoms from the gastrointestinal system , like diarrhea and nausea [ 12 , 28 ] . further studies are needed to address the issue of eating disorders and to explain the reason for the low bmi . many medical conditions present with long lasting fatigue as a disabling symptom [ 29 , 30 ] . in this retrospective study , this is a reminder of the importance of a thorough investigation of the children being evaluated for possible cfs , to exclude other causes for their fatigue . the clinical assessment of children and adolescents with possible cfs needs systematic investigation . nutritional status , possible eating disorder , and psychosocial issues need to be addressed and evaluated carefully .
aim . to estimate number of children being diagnosed with chronic fatigue syndrome ( cfs ) . 
 methods . for a period of 10 years ( 20022011 ) data from children being referred for fatigue symptoms were collected retrospectively . 
 results . 
 thirty - seven children were referred . 
 four were excluded due to incorrect coding . 
 six ( 18% ) patients received other diagnoses at the end of evaluation time . 
 of the 27 who received the diagnosis g93.3 , four had a previous chronic illness , while 23 patients were previously healthy . 
 all patients reported onset of fatigue symptom in relation to an infection , and all tested positive for igg to either epstein - barr virus , cytomegalovirus or borrelia , indicating previous infection . 
 there were 16 ( 59% ) boys among the 27 patients . 
 the mean age at the debut of fatigue symptoms was 141 months ( sd 30 ) for boys and 136 months ( sd 31 ) for girls , respectively . 
 being underweight , defined as bmi < 17.5 , was found in 12 ( 44% ) patients . 
 conclusion . 
 an increasing number of children and adolescents are evaluated for cfs . 
 the clinical assessment of children and adolescents with possible cfs need systematically evaluation 
 . nutritional status , possible eating disorder , and psychosocial issues need to be addressed and evaluated carefully . 
 a multidisciplinary approach is essential when assessing cfs in children and adolescents . 
 there is a need for european guidelines .