Fatigue symptoms

Fatigue is a very common symptom associated with a wide range of medical conditions. Because fatigue is difficult to define and measure, estimates of the prevalence of fatigue tend to be imprecise. UK community surveys suggest that around 20% men and 30% women have suffered from ‘always feeling tired’ in the past month. Studies that have asked primary care attenders whether they have been troubled by fatigue find that 10 to 30% respond positively, although possibly as few as 1 in 10 of these will present with fatigue as their primary problem.

Many fatigued patients will have a medical condition that might account for their fatigue, but a quarter to a half will not. The prevalence of medically unexplained fatigue in UK primary care consulters has been variously estimated at around 10–15%. Epidemiological studies find that women are about 1.5 times more likely to be fatigued than men. The sex ratio is higher for cases with more severe or more chronic fatigue and lower if those with comorbid psychiatric disorders are excluded. Fatigue may be under-recognised in patients from Black and minority ethnic sections of the community.

Chronic fatigue syndrome

Chronic fatigue syndrome (CFS, also known as ME and usually abbreviated to CFS/ME), is a condition in which the principal complaint is severe, disabling fatigue unexplained by other medical conditions, of at least 6 months duration. CFS/ME is associated with high levels of impairment, and social and economic costs. Preliminary evidence suggests that both mood disturbance (depression and anxiety) and a tendency to a driven, ‘all-or-nothing’ approach to managing symptoms, are associated with the progression to a more chronic fatigue state. A number of sets of diagnostic criteria for CFS/ME have been developed, each providing difference prevalence estimates, but in the UK, the prevalence is usually quoted as 0.2–0.4% of the population. Thus, many more patients experience unexplained sustained fatigue than meet the requirements for a diagnosis of CFS/ME.

Fatigue is a subjective feeling like pain, and is not directly measurable. Unlike some symptoms in this book, fatigue is a feeling familiar to us all. Studies in the general population have shown that fatigue lies on a continuum. Fatigue becomes a problem when it is experienced out of proportion to the level of exertion or work undertaken, and when it reaches a certain level of severity, chronicity and impact on a person’s life. It is perhaps because fatigue is so familiar that it is not always recognised and treated.

GPs should take complaints of persistent fatigue seriously, not only because fatigue may be a symptom of a condition that requires treatment, but also because it is so distressing, and can become chronic and very disabling.

The term medically unexplained is somewhat misleading because it suggests that fatigue in the context of other conditions is medically explained. In fact, even when fatigue is an established feature of a condition, the causes and processes underlying fatigue are often poorly understood—to this extent, all fatigue is unexplained. Furthermore, programmes for treating fatigue in conditions such as cancer, rheumatoid arthritis, multiple sclerosis, and post-stroke tend to adopt the same approaches as those that are successful in managing medically unexplained fatigue, suggesting that the explained/unexplained distinction is not always very illuminating.

In primary care samples, severity of fatigue is strongly associated with distress. In the case of CFS/ME, fatigue is usually accompanied by muscle pain, sleep disturbance (hypersomnia, insomnia, disturbed sleep–wake cycles, and waking unrefreshed), mood disturbance, and memory and concentration problems (often termed ‘mental fatigue’). Other symptoms and syndromes are also commonly associated with fatigue, such as dizziness, nausea and malaise, and the symptoms of IBS.

Certain infections, for example glandular fever, place patients at greater risk of developing prolonged fatigue, but a substantial minority of patients with prolonged fatigue are unable to pinpoint any particular trigger. Patients with sleep problems often report daytime fatigue, but in some cases may actually be experiencing excessive daytime sleepiness. It is important to consider whether fatigue is secondary to poor sleep (including poor sleep due to depression). In many cases, however, fatigue coexists with normal or increased sleep, although that sleep may be experienced as unrefreshing.

Fatigue is non-specific, and is known to be associated with many medical conditions. In fact, patients with fatiguing conditions (such as rheumatoid arthritis, multiple sclerosis and even cancer) often say that fatigue is their most troubling symptom. In terms of what it feels like for the patient, there is no easy way to distinguish fatigue that is a symptom of one of these conditions from fatigue that is not – that is, fatigue may feel similar whatever is underlying it.

In order to rule out other possible causes of fatigue, look for additional signs and symptoms that may be associated with those other conditions. The NICE guidelines for CFS/ME identify a number of ‘red flag’ features that should always be investigated. These are listed in Box 12.1.