Dyspepsia is a symptom or a combination of symptoms that alerts a clinician to the presence of an upper gastrointestinal (UGI) problem. Typical symptoms include epigastric pain or burning, early satiety and post-prandial fullness, belching, bloating, nausea, or discomfort in the upper abdomen. Symptoms are the central focus of this assessment; it is therefore essential that they are described in a manner that is relevant to patients. 
Clinicians using symptom-based assessment of UGI symptoms need to be aware of the diagnostic uncertainty inherent in this approach. These assessments can provide functional working diagnoses, but there is always a danger of misclassification. An important consequence of the inability to make a definitive diagnosis based on symptoms alone is an over-diagnosis of GORD and the under-recognition of Helicobacter pylori -related disease. Periodic reassessment can add a layer of safety, but the timing and frequency of reassessment needs to be individualised. 
The nomenclature for dyspepsia is confusing. This is largely because some medical organisations include all UGI symptoms in the term dyspepsia, then separate patients with symptoms suggesting GORD for appropriate management, whereas others recognise the overlap in symptoms between the various causes of UGI symptoms but choose to separate the symptoms suggesting GORD before applying the term dyspepsia. Both approaches recommend identifying patients whose symptoms suggest GORD and managing them as having reflux disease.
The American College of Gastroenterology and the Canadian Association of Gastroenterology have published joint guidelines for the management of dyspepsia.  The operational definition for dyspepsia used in the guideline is predominant epigastric pain. The authors recognise that patients may present with nausea, vomiting, or fullness but, providing that the patient’s primary concern is epigastric pain, they should be managed as patients with dyspepsia.
A technical review from the American Gastroenterological Association for the evaluation of dyspepsia excludes patients with symptoms that suggest GORD, and includes only those with the typical symptoms listed above.  The UK National Institute for Health and Care Excellence guideline on GORD and dyspepsia in adults was last updated in 2014,  and although both GORD and dyspepsia are considered, a discrete algorithm is suggested for patients with symptoms typical of GORD.
Patients with dyspepsia can be classified based on the type or outcomes of the investigations they have received. Research papers often refer to different categories of patients with dyspepsia, so it is important to understand the descriptions of the most common subgroups that have been described.
Uninvestigated dyspepsia is classified as a condition with characteristic symptoms clinically assessed to be originating in the upper gastrointestinal (UGI) tract, but which has not been recently investigated by UGI endoscopy.    Symptoms include epigastric pain or burning, early satiety and post-prandial fullness, belching, bloating, nausea, or discomfort in the upper abdomen.
Functional dyspepsia (sometimes called non-ulcer dyspepsia) refers to a situation where UGI endoscopy did not reveal a potential cause for the dyspepsia. It is generally reserved for patients with a normal endoscopy whose symptoms do not suggest GORD. (Patients with GORD with normal endoscopy are said to have non-erosive reflux disease.)   
The new Rome IV classification sub-divides functional dyspepsia into 3 categories: 
Post-prandial distress syndrome (PDS), which is characterised by meal-induced dyspeptic symptoms, such as discomfort, pain, nausea, and fullness
Epigastric pain syndrome (EPS), which refers to epigastric pain, or epigastric burning, that does not occur exclusively post-prandially, can occur during fasting, and can even be improved by meal ingestion
Overlapping PDS and EPS, which is characterised by meal-induced dyspeptic symptoms and epigastric pain or burning.
GORD and dyspepsia are related and may overlap. Patients with troublesome heartburn and/or acid regurgitation can be diagnosed clinically as having GORD.  It is known that many patients with GORD will have atypical presentations such as epigastric burning or pain, and therefore their symptoms will cause them to be placed into the group of uninvestigated patients with dyspepsia. More than half of patients with GORD have a normal oesophagus at endoscopy.
There is now widespread agreement that patients with troublesome heartburn and/or acid regurgitation can generally be diagnosed clinically as having GORD, without the need for endoscopy. 
The extent or severity of the patient's dyspepsia is measured by the patient's report of the impact of symptoms on quality of life and function. The patient's assessment of the severity of dyspepsia usually relates to the degree to which it affects work, sleep, diet, or leisure.  
A meta-analysis of population-based studies evaluating the prevalence of uninvestigated dyspepsia found a pooled prevalence of 20.8% (95% CI 17.8% to 23.9%).  The prevalence varied according to country (1.8% to 57.0%) and the criteria used to define dyspepsia. The greatest prevalence values were found when a very broad definition of dyspepsia was used (29.5%; 95% CI 25.3% to 33.8%). When upper abdominal or epigastric pain or discomfort was used the prevalence was lower (20.4%; 95% CI 16.3% to 24.8%). The prevalence was higher in women (OR 1.24; 95% CI 1.13 to 1.36), smokers (OR 1.25; 95% CI 1.12 to 1.40), people taking non-steroidal anti-inflammatory drugs (OR 1.59; 95% CI 1.27 to 1.99), and people positive for Helicobacter pylori (OR 1.18; 95% CI 1.04 to 1.33).
An internet-based cross-sectional health survey found that Rome IV functional dyspepsia is significantly more prevalent in the US (232 [12%] of 1949 responses) than in Canada (167 [8%] of 1988 responses) and the UK (152 [8%] of 1994 responses; p<0·0001).  The sub-type distribution was 61% post-prandial distress syndrome, 18% epigastric pain syndrome, and 21% overlapping variant with both syndromes; this pattern was similar across countries.
There is evidence of special issues relating to functional dyspepsia in women.  Dyspepsia has been shown to have a significant negative impact on quality of life. The impact relates to changes in sleep, diet, and interference with work and leisure activities. Women who have experienced emotional or physical abuse appear to be particularly vulnerable to developing functional dyspepsia and irritable bowel syndrome (IBS).
There is much overlap between functional dyspepsia and IBS. Patients who have both disorders have a substantially greater symptom burden and are more likely to consult a physician. 
Clinical Adjunct Professor
School of Medicine and Public Health
University of Wisconsin
NV has consulted for Ironwood Pharmaceuticals, Otsuka Pharmaceutical, Shire Pharmaceuticals, and Astellas Pharma. He has received research grants from Impleo Medical and Allergan.
Dr Nimish Vakil would like to gratefully acknowledge Dr Nigel W. Flook, a previous contributor to this topic.
Professor of Medicine
Chief of GI Endoscopy
Rikshospitalet University Hospital
LA declares that he has no competing interests.
Chief of Service
Hôpital Hôtel-Dieu de Québec
Centre Hospitalier Universitaire de Québec
MB declares that he has no competing interests.
Division of Gastroenterology
Department of Medicine
McMaster University Medical Centre
PM is an author of a number of references cited in this topic.
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