The differences between the concepts of myalgic encephalomyelitis (ME) and chronic fatigue syndrome (CFS) are discussed with particular reference to the problems arising from the multiple definitions of fatigue. It is pointed out that our earliest published work with ME patients showed altered blood rheology and subsequent tests using scanning electron microscopy of immediately fixed blood samples provided a basis for understanding the poor blood filterability described earlier.

The consequences of stiffened, shapechanged red cells would be to impair capillary blood flow particularly in tissues with smaller than usual mean capillary diameters. The degree of reduction in the rates of delivery of oxygen and nutrient substrates would be related to symptom severity. As there have been a number of previously reported studies of the red cells in a number of chronic disorders, the obsevation is not new. Furthermore, the changes in red cell shape pop iw twits which occur in ME also occur in Guici chronic disorders so red cell shape analysis alone is not diagnostic for ME. The observed changes are probably of importance in the pathogenesis of tiredness.

Patients benefit from the results of red cell shape analysis test as it provides evidence of a change which can explain their illness, even if they are unresponsive to treatment. As changes in rheology can be shown to occur in the blood of ME patients, haemorheologic agents which have the potential to improve the flow properties of blood are recommended as therapeutic agents.