Using a standardised assessment, we studied 365 patients referred with suspected CFS/ME. Of these, 13.2 % were diagnosed based on the Canadian criteria. A further 4.9 % received a diagnosis of postviral fatigue syndrome, but did not fulfil the criteria for CFS/ME.
Most of the diagnoses were encompassed by ICD-10 Chapter V(F), of which anxiety and depression disorders constituted the majority. This confirms that mental disorders are highly important differential diagnoses with regard to symptoms of fatigue and lack of energy, as well as additional symptoms in the form of pain, impaired memory and concentration, and other symptoms that are included in the symptom complex surrounding CFS/ME.
In this study, evaluation by a specialist in psychiatry or psychology was an integral part of the assessment, and included a clinical interview and use of recognised forms. This has ensured a uniform assessment. Only two of 48 patients with a final diagnosis of CFS/ME were additionally diagnosed with a mental condition. This is somewhat in contrast to studies that have shown anxiety and depression to be common in patients with CFS/ME (21, 22).
According to the Canadian criteria, primary psychiatric conditions are exclusion diagnoses for CFS/ME, but anxiety and depression disorders may be regarded as comorbid conditions. Less psychopathology is found in patients who fulfil the Canadian criteria than in those who fulfil the Fukuda criteria (23). The final assessment as to whether the patient primarily has an anxiety and depression disorder, or whether this is secondary to a condition of persistent fatigue, will be based on a total assessment of the medical history and examination. Discretion is a factor in these assessments, since existing sets of criteria do not draw an unambiguous distinction between CFS/ME and cases in which the fatigue is secondary to mental illness.
There was no overlap between fibromyalgia and CFS/ME either – none of the 16 patients diagnosed with fibromyalgia received the latter diagnosis. Fibromyalgia has many features in common with CFS/ME (24), and it can be difficult to distinguish between the conditions. In this study, the diagnosis of fibromyalgia was made by a rheumatologist, either in this or an earlier assessment. In the fibromyalgia patients, persistent pain was clearly a precursor to fatigue, and we considered that the symptom complex could be explained on this basis. However, it is evident that some diagnostic uncertainty exists between CFS/ME and fibromyalgia, as is also the case for other overlapping conditions, for example irritable bowel syndrome (22, 25).
With few exceptions, the patients were referred from the primary healthcare service and had not previously been assessed specifically for CFS/ME in the specialist health services. We endeavoured to ensure that the assessment would be a low-threshold service for primary healthcare. Nevertheless, many patients were rejected when the diagnosis of CFS/ME was excluded, based on the information in the referral. The number of rejected referrals is not recorded, but this selection indicates that the proportion of referred patients who fulfil the criteria for CFS/ME is considerably lower than 13.2 %, as reported here.
As a consequence of capacity limitations in the radiological department, many patients underwent MRI examination in the outpatient clinic following assessment. From a neurological standpoint, this examination will have been conducted mainly to exclude demyelinating disease. MRI of the brain according to the multiple sclerosis protocol is, in our opinion, sufficient. Since MRI examination following the hospital assessment leads to uncertainty when discussing the diagnosis, we now request that the referring doctor arranges for the examination to be performed in advance.
Pathological cerebrospinal fluid was found in five patients. Altogether 14 patients experienced post-lumbar puncture headache requiring an epidural blood patch. Pathological cerebrospinal fluid resulted in further investigation in three patients, with repeated MRI examinations and lumbar punctures. No specific diagnosis was made for these patients. Lumbar puncture is now performed only when clearly indicated, for example when MRI findings may indicate demyelinating disease, and not routinely.
Orthostatic intolerance is known to occur in cases of CFS/ME (26), and patients with postural orthostatic tachycardia are considered a clinical subgroup of these patients (27, 28). Orthostatic intolerance is also suggested as one of two supplementary SEID criteria (15). Only four of our patients experienced a fall in blood pressure. There was no difference between the patients with CFS/ME and the other patients.
In an examination of 365 patients, only one was found to have an underlying somatic condition (adrenal insufficiency) that had not been recognised and that could explain their fatigue. Cerebral venous sinus thrombosis was identified in one patient – but this could not explain the symptoms of persistent fatigue for which the patient was being assessed, and it was interpreted as a coincidence. Two patients are being monitored for possible somatic illness after findings of MR lesions that may indicate inflammation or low-grade glioma. This indicates that patients with suspected CFS/ME are thoroughly investigated for somatic illnesses in the primary health service.
Self-reporting forms for degree of fatigue showed little difference between those who were diagnosed with CFS/ME and those who received other diagnoses. We consider that the FSS form is unsuited for distinguishing CFS/ME from other conditions that involve fatigue. However, patients with the diagnosis scored above the threshold value on the HADS form less frequently than others, and this was the case for anxiety as well as depression. In our view, the HADS form may constitute a useful tool in differential diagnostic assessment of suspected CFS/ME.
Duration of symptoms was not recorded in this study. Most patients had had symptoms for several years before they attended for assessment. It is therefore essential that patients are assessed both somatically and psychiatrically in the primary health service before referral to the specialist health services. It is especially important to thoroughly assess psychosocial conditions in patients who present with this type of symptom complex. Anxiety and depression are serious conditions that are amenable to treatment, and long waiting times in the specialist health services may be very unfavourable for these patients if they go untreated.
It may also be called into question whether assessment of CFS/ME should take place in a neurological department, or whether other departments would be more appropriate. The diagnosis is found in the neurological chapter of ICD-10 (G93.3), but there is little by way of evidence from assessments that points unequivocally towards neurological disease. What is most important in our opinion is that the patients are examined systematically – it is of less importance which department performs the assessment. Following a standard assessment, with time, resources and availability of professionals from different specialties, the clinical assessment of suspected CFS/ME could be conducted with good precision in the course of a few days of elective hospitalisation.
In our opinion, for many the assessment must be conducted in the primary health service, based on the national guidelines from the Norwegian Directorate of Health (11). A detailed patient history, blood sample analysis and MRI examination of the brain and spinal cord are indicated. The assessment must also include specific evaluation of mental disorders, in particular anxiety and depression disorders.
In the absence of biomarkers for the condition, in the majority of cases assessment and diagnosis will need to be aimed at identifiable causes of fatigue, both somatic and mental, and findings of these will consequently explain the symptoms, and therefore exclude the diagnosis of CFS/ME. Given a structured assessment in the primary health service, our assumption is that the need for assessment in the specialist health services will be reduced and can be reserved for patients for whom the diagnosis is uncertain.