Is chronic fatigue syndrome associated with platelet activation? Kennedy, Gwen; Norris, Gillian; Spence, Vance; McLaren, Margaret; Belch, Jill JF Vascular Diseases Research Unit, University Department of Medicine, Ninewells Hospital & Medical School, Dundee, UK Received 11 December, 2003 Revised 8 April, 2004 Accepted 15 April, 2004 Correspondence and requests for reprints to Dr Gwen Kennedy, Vascular Diseases Research Unit, University Department of Medicine, Ninewells Hospital & Medical School, Dundee DD1 9SY, UK Tel: +44 1382 632432; fax: +44 1382 632333; e-mail: firstname.lastname@example.org Sponsorship: The study was funded by the charity ME Research Group for Education and support (MERGE), Perth, UK and a grant from the Anonymous Trust, Ninewells Hospital & Medical School, Dundee, UK. Further support was also received from the Sir John Fisher Foundation (Educational Grant) Abstract: Chronic fatigue syndrome (CFS) is a debilitating condition that has no known aetiology or pathophysiology. Recent investigations by other workers have suggested that individuals with CFS may have a hypercoagulable state. This study investigated various aspects of platelet activation and function in 17 patients with CFS and in 16 age-matched and sex-matched healthy controls. Platelet aggregation, platelet volume and coagulation tests were performed. Platelet aggregation was investigated by means of the photometric changes using citrated platelet-rich plasma, whole blood aggregation was calculated as the percentage fall in single platelet counts and the coagulation tests were performed on an automatic microcentrifugal analyser. A trend was observed for the patients to have lower aggregation results and a reduced mean platelet volume. However, this only reached statistical significance for one result; the rate of the aggregation slope by 1.0 μg/ml collagen [CFS patients, 18 (9-28) versus controls, 32.5 (19-36); Mann-Whitney U test, P = 0.029]. No significant differences were found for any of the measurements of coagulation. These results are in contrast to previously reported findings. However, due to the heterogeneous nature of the disease, and the resulting lifestyles of the patients, caution should be taken when comparing one group of patients with another. Nevertheless, we certainly found no evidence of increased platelet activation or of a hypercoagulable state in patients with CFS and, on the basis of these results, anti-platelet or anti-coagulant therapy is not warranted. Introduction: Chronic fatigue syndrome (CFS) is an illness of unknown aetiology associated with debilitating fatigue of at least 6 months duration and accompanied by a variety of symptoms suggestive of immune and neuroendocrine disturbances and abnormalities within the central nervous system. Although there are many reports pointing to chronic low-level immune activation within many CFS patients [1,2], no relationship has yet been established between such abnormalities and patients' symptoms. One group of researchers in particular , however, has hypothesized that CFS is a hypercoagulable state based on a model linking pathogen activated inflammation to cytokine modulation of the coagulation system [3,4]. Their model implicates immunological disturbances  and viral infections  are central to the hypercoagulable state, and they have also suggested that anticoagulant proteins such as protein C and protein S are associated with defects in fibrinolysis in this patient group . They have further suggested that activation of coagulation may be a final common endpoint of a variety of CFS-like illnesses such as fibromyalgia and Gulf War Illness . In support of this, our group has recently shown that patients with CFS had significantly elevated platelet poor plasma levels of transforming growth factor-β1 and an increased expression of annexin V binding to neutrophils when compared with healthy, matched controls . Transforming growth factor-β1 is a multi-functional cytokine that is stored in the α granules of circulating platelets, is released during platelet activation and may be involved in platelet aggregation . Annexin V is an anticoagulant protein that preferentially binds to negatively charged phospholipids such as phosphatidylserine, which is expressed on the outer leaflet of the cytoplasmic membrane during the apoptotic process. Phosphatidylserine can induce procoagulant responses  so an increased expression of annexin V could also reflect a procoagulant tendency. The observation of potential markers of platelet activation by us alongside the previous work by Berg and colleagues suggest that there may be altered platelet function in patients with CFS that requires further investigation. In order to elucidate this further we set out to investigate platelet function in patients with a well-documented history of CFS alongside a comparable group of healthy control subjects. [ . . . ] Discussion: The CFS patients in this study showed no evidence of increased platelet activation or hypercoagulability when compared with healthy matched control subjects. These results contrast with previously reported findings in CFS patients and bring into question the conclusion by Berg and colleagues [3,4] that CFS is an immune system activation of coagulation. It is worth examining factors that might have contributed to these contrasting results; that is, the results reported here showing no differences in coagulation pathways between CFS patients and matched controls and those by Berg's group showing hypercoagulation in CFS subjects. In the first place CFS is a heterogeneous condition, and it is possible that we are looking at an entirely unrelated cohort of CFS patients with a different aetiology and symptom expression to that of Berg et al. Our CFS patient population has been strictly selected to fulfil the specific criteria of the Centers for Disease Control 1994 definition  and are representative of the large cohort of patients in our research database. In the paper by Berg et al. , however, they conducted a blinded prospective study of 54 CFS and/or fibromyalgia patients and 23 controls, and this is clearly a broader case-definition than that used by us. Indeed, we have recently reported that fibromyalgia patients are biologically different to CFS patients in a number of key ways . In a further paper, Brewer and Berg  investigated 30 patients with CFS who have at least had one positive blood culture for active human herpesvirus-6, and they report that samples were taken in the morning and that none of the patients were on anticoagulant therapy. The results in this second study were reported as being positive from a panel of tests, with no results or equivalent control data provided. Of further concern is the fact that there is no information about age, gender, smoking status, current medications or blood sampling methods in the Berg et al. paper, and all of these are known to affect coagulation pathways. It should also be stressed that there are gender differences in platelet aggregation, with higher levels being reported in women . Although CFS female patients outnumber males by approximately 3: 1 , we had equal number of both sexes within our patient and control populations. Similar information on gender ratios is not available in the research reported by Berg et al. Exercise also influences platelet activity, especially in those who lead a sedentary lifestyle when compared with those who are physically trained , and an increase in platelet-platelet aggregates occurs after exercise . This is of particular significance in a patient population who, by definition, have a substantial reduction in previous levels of occupational, educational, social or personal activities . CFS is also characterized by post-exertional malaise with patients having less intense and shorter activity peaks followed by longer rest periods , often for as long as 24 h after the activity. Such an activity cycle might actually be expected to reduce platelet aggregation given the finding that 45 min of supine rest in a calm environment led to a highly significant decrease in platelet activation . In general, although there were no significant differences between platelet aggregation in our CFS population when compared with matched control subjects, the trend was for lower activity and caution is required when interpreting data from this patient group given the gender bias and the fact that many patients have a sedentary lifestyle. This study was planned to further investigate the work by Berg and colleagues and the tenuous observations made by us from early work. On the whole no significant differences in platelet function were found between the patients with CFS and control subjects. CFS is, however, a heterogeneous illness and patients have a variety of adapted lifestyles, so caution is needed when comparing one group of patients with another. In this study there is certainly no evidence of increased platelet activation or that a hypercoagulable state exists in patients with CFS, and, on the basis of these results, a study of anti-platelet therapy in CFS patients is not warranted.