Visceral pain is pain that results from the activation of nociceptors of the thoracic, pelvic, or abdominal viscera (organs). Visceral structures are highly sensitive to distension (stretch), ischemia and inflammation, but relatively insensitive to other stimuli that normally evoke pain such as cutting or burning.
Visceral pain is diffuse, difficult to localize and often referred to a distant, usually superficial, structure. [1] It may be accompanied by symptoms such as nausea, vomiting, changes in vital signs as well as emotional manifestations. The pain may be described as sickening, deep, squeezing, and dull. [2] Distinct structural lesions or biochemical abnormalities explain this type of pain in only a proportion of patients. These diseases are grouped under gastrointestinal neuromuscular diseases (GINMD). Others can experience occasional visceral pains, often very intense in nature, without any evidence of structural, biochemical or histolopathologic reason for such symptoms. These diseases are grouped under functional gastrointestinal disorders (FGID) and the pathophysiology and treatment can vary greatly from GINMD. The two major single entities among functional disorders of the gut are functional dyspepsia and irritable bowel syndrome. [3]
Visceral hypersensitivity is hypersensitive visceral pain perception, which is commonly experienced by individuals with functional gastrointestinal disorders. [4]
In the past, viscera were considered insensitive to pain but now it is clear that pain from internal organs is widespread and that its social burden may surpass that of pain from superficial (somatic) sources. Myocardial ischemia, the most frequent cause of cardiac pain, is the most common cause of death in the United States. [5] Urinary colic produced from ureteral stones has been categorized as one of the most intense forms of pain that a human being can experience. The prevalence of such stones has continuously increased, reaching values of over 20% in developed countries. [6] [7] Surveys have shown prevalence rates among adults of 25% for intermittent abdominal pain and 20% for chest pain; 24% of women experience pelvic pain at any point in time. For over two-thirds of those affected, pain is accepted as part of daily life and symptoms are self-managed; a small proportion defer to specialists for help. Visceral pain conditions are associated with diminished quality of life, and exert a huge cost burden through medical expenses and lost productivity in the workplace. [8]
Visceral pain should be suspected when vague midline sensations of malaise are reported by a patient. True visceral pain is characterized as a vague, diffuse, and poorly defined sensation. [9] [10] Regardless of specific organ of origin, the pain is usually perceived in the midline spanning anywhere from the lower abdomen up to the chest. In the early phases the pain is perceived in the same general area and it has a temporal evolution, making the onset sensation insidious and difficult to identify. [11]
The pain is typically associated with involvement of the autonomic nervous system. Some of these symptoms include pallor, sweating, nausea, vomit, changes in vital signs including blood pressure, heart rate and/or temperature. Strong emotional reactions are also common presenting signs and may include anxiety, anguish and a sense of impending doom. Visceral pathology may also manifest only through emotional reactions and discomfort where no pain is reported. The intensity of visceral pain felt might have no relationship to the extent of internal injury. [11] [12]
Visceral pain changes in nature as it progresses. Pain from a specific organ can be experienced, or "referred" to different sites of the body. There is no pathology or no cause for pain at these referred somatic sites however the pain will be experienced at this location, often with significant intensity. Referred pain is sharper, better localized, and less likely to be accompanied by autonomic or emotional signs. [10] [12]
A good example of visceral pain that is common place and embodies the wide spectrum of clinical presentations discussed above is a myocardial infarction (MI), more commonly known as a heart attack. This pain is secondary to ischemia of the cardiac tissue. The most common presenting symptom is chest pain that is often described as tightness, pressure or squeezing. The onset of symptoms is usually gradual, over several minutes and tends to be located in the central chest (overlying the sternum) although it can be experienced in the left chest, right chest, and even abdominal area. Associated symptoms, which are mostly autonomic in nature, include diaphoresis, nausea, vomiting, palpitations, and anxiety (which is often described as a sense of impending doom). [13] [14] Referred pain is experienced most commonly radiating down the left arm however it can also radiate to the lower jaw, neck, back and epigastrium. Some patients, especially elderly and diabetics, may present with what is known as a painless myocardial infarction or a "silent heart attack". A painless MI can present with all of the associated symptoms of a heart attack, including nausea, vomiting, anxiety, heaviness, or choking, but the classic chest pain described above is lacking. [9] [15]
It is always important for not only the physician but also the patient to remember the dissociation between magnitude of injury to internal organs and the intensity of pain and how this can be potentially dangerous if overlooked, for example a silent heart attack. [16] More rarely intense visceral pain does not signify a significant pathologic process, for example intense gas pains.
The vague and poorly defined sensation as well as its temporal nature, characteristic of visceral pain, is due to the low density of sensory innervation of viscera and the extensive divergence of visceral input within the central nervous system (CNS). [9] [10] The phenomenon of referred pain is secondary to the convergence of visceral afferent (sensory) nerve fibers entering the spinal cord at the same level as the superficial, somatic structures experiencing the pain. This leads to a misinterpretation of incoming signals by higher brain centers. [10] [12]
There are two goals when treating visceral pain:
Treatment of the pain in many circumstances should be deferred, until the origin of the symptoms has been identified. Masking pain may confound the diagnostic process and delay the recognition of life-threatening conditions. Once a treatable condition has been identified there is no reason to withhold symptomatic treatment. Also, if cause for the pain is not found in reasonable time then symptomatic treatment of the pain could be of benefit to the patient in order to prevent long-term sensitization and provide immediate relief. [11] [17] [18]
Symptomatic treatment of visceral pain relies primarily upon pharmacotherapy. Since visceral pain can result secondary to a wide variety of causes, with or without associated pathology, a wide variety of pharmacological classes of drugs are used including a variety of analgesics (ex. opiates, NSAIDs, cannabinoids), antispasmodics (ex. loperamide, benzodiazepines), antidepressants (ex. TCA, SSRI, SNRI) as well as others (ex. ketamine, clonidine, gabapentin). In addition, pharmacotherapy that targets the underlying cause of the pain can help alleviate symptoms due to lessening visceral nociceptive inputs. [7] For example, the use of nitrates can reduce anginal pain by dilating the coronary arteries and thus reducing the ischemia causing the pain. The use of spasmolytics (antispasmodics) can help alleviate pain from a gastrointestinal obstruction by inhibiting the contraction of the gut. [9] There are issues associated with pharmacotherapy that include side effects (ex. constipation associated with opiate use), chemical dependence or addiction, and inadequate pain relief.
Invasive therapies are in general reserved for patients in whom pharmacological and other non-invasive therapies are ineffective. A wide variety of interventions are available and shown to be effective, a few will be discussed here. Approximately 50–80% of pelvic cancer pain patients benefit from nerve blocks. [19] [20] Nerve blocks offer temporary relief and typically involve injection of a nerve bundle with either a local anesthetic, a steroid, or both. Permanent nerve block can be produced by destruction of nerve tissue. Strong evidence from multiple randomized controlled trials support the use of neurolytic celiac plexus block to alleviate pain and reduce opioid consumption in patients with malignant pain originating from abdominal viscera such as the pancreas. [21] Neurostimulation, from a device such as a spinal cord stimulator (SCS), for refractory angina has been shown to be effective in several randomized controlled trials. [22] [23] A SCS may also be used for other chronic pain conditions such as chronic pancreatitis and familial Mediterranean fever. Other devices that have shown benefit in reducing pain include transcutaneous electrical nerve stimulators (TENS), targeted field stimulation, both used for somatic hyperalgesic states, external neuromodulation, pulsed radiofrequency ablation and neuraxial drug delivery systems. [16] [24]
Angina, also known as angina pectoris, is chest pain or pressure, usually caused by insufficient blood flow to the heart muscle (myocardium). It is most commonly a symptom of coronary artery disease.
Heartburn, also known as pyrosis, cardialgia or acid indigestion, is a burning sensation in the central chest or upper central abdomen. Heartburn is usually due to regurgitation of gastric acid into the esophagus. It is the major symptom of gastroesophageal reflux disease (GERD).
Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart.
Chest pain is pain or discomfort in the chest, typically the front of the chest. It may be described as sharp, dull, pressure, heaviness or squeezing. Associated symptoms may include pain in the shoulder, arm, upper abdomen, or jaw, along with nausea, sweating, or shortness of breath. It can be divided into heart-related and non-heart-related pain. Pain due to insufficient blood flow to the heart is also called angina pectoris. Those with diabetes or the elderly may have less clear symptoms.
Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Since the abdomen contains most of the body's vital organs, it can be an indicator of a wide variety of diseases. Given that, approaching the examination of a person and planning of a differential diagnosis is extremely important.
Functional gastrointestinal disorders (FGID), also known as disorders of gut–brain interaction, include a number of separate idiopathic disorders which affect different parts of the gastrointestinal tract and involve visceral hypersensitivity and motility disturbances.
Polyarteritis nodosa (PAN) is a systemic necrotizing inflammation of blood vessels (vasculitis) affecting medium-sized muscular arteries, typically involving the arteries of the kidneys and other internal organs but generally sparing the lungs' circulation. Small aneurysms are strung like the beads of a rosary, therefore making this "rosary sign" an important diagnostic feature of the vasculitis. PAN is sometimes associated with infection by the hepatitis B or hepatitis C virus. The condition may be present in infants.
Referred pain, also called reflective pain, is pain perceived at a location other than the site of the painful stimulus. An example is the case of angina pectoris brought on by a myocardial infarction, where pain is often felt in the left side of neck, left shoulder, and back rather than in the thorax (chest), the site of the injury. The International Association for the Study of Pain has not officially defined the term; hence, several authors have defined it differently. Referred pain has been described since the late 1880s. Despite an increasing amount of literature on the subject, the biological mechanism of referred pain is unknown, although there are several hypotheses.
A hypertensive emergency is very high blood pressure with potentially life-threatening symptoms and signs of acute damage to one or more organ systems. It is different from a hypertensive urgency by this additional evidence for impending irreversible hypertension-mediated organ damage (HMOD). Blood pressure is often above 200/120 mmHg, however there are no universally accepted cutoff values.
Unstable angina is a type of angina pectoris that is irregular or more easily provoked. It is classified as a type of acute coronary syndrome.
Postcholecystectomy syndrome (PCS) describes the presence of abdominal symptoms after a cholecystectomy.
A hemorrhagic infarct is determined when hemorrhage is present around an area of infarction. Simply stated, an infarction is an area of dead tissue or necrosis. When blood escapes outside of the vessel (extravasation) and re-perfuses back into the tissue surrounding the infarction, the infarction is then termed a hemorrhagic infarct (infarction). Hemorrhagic infarcts can occur in any region of the body, such as the head, trunk and abdomen-pelvic regions, typically arising from their arterial blood supply being interrupted by a blockage or compression of an artery.
Abdominal epilepsy is a rare condition most frequently found in children, consisting of gastrointestinal disturbances caused by epileptiform seizure activity. Though a few cases of it have been reported in adults too. It has been described as a type of temporal lobe epilepsy. Responsiveness to anticonvulsants can aid in the diagnosis. Distinguishing features of abdominal epilepsy include (1) Abnormal laboratory, radiographic, and endoscopic findings revealing paroxysmal GI manifestations of unknown origin (2) CNS symptoms (3) Abnormal EEG. Most published medical literature dealing with abdominal epilepsy is in the form of individual case reports. A 2005 review article found a total of 36 cases described in the medical literature.
Mitochondrial neurogastrointestinal encephalopathy syndrome (MNGIE) is a rare autosomal recessive mitochondrial disease. It has been previously referred to as polyneuropathy, ophthalmoplegia, leukoencephalopathy, and intestinal pseudoobstruction. The disease presents in childhood, but often goes unnoticed for decades. Unlike typical mitochondrial diseases caused by mitochondrial DNA (mtDNA) mutations, MNGIE is caused by mutations in the TYMP gene, which encodes the enzyme thymidine phosphorylase. Mutations in this gene result in impaired mitochondrial function, leading to intestinal symptoms as well as neuro-ophthalmologic abnormalities. A secondary form of MNGIE, called MNGIE without leukoencephalopathy, can be caused by mutations in the POLG gene.
In medicine, Carnett's sign is a finding on clinical examination in which (acute) abdominal pain remains unchanged or increases when the muscles of the abdominal wall are tensed. For this part of the abdominal examination, the patient can be asked to lift the head and shoulders from the examination table to tense the abdominal muscles. An alternative is to ask the patient to raise both legs with straight knees.
Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the throat.
Coronary ischemia, myocardial ischemia, or cardiac ischemia, is a medical term for abnormally reduced blood flow in the coronary circulation through the coronary arteries. Coronary ischemia is linked to heart disease, and heart attacks. Coronary arteries deliver oxygen-rich blood to the heart muscle. Reduced blood flow to the heart associated with coronary ischemia can result in inadequate oxygen supply to the heart muscle. When oxygen supply to the heart is unable to keep up with oxygen demand from the muscle, the result is the characteristic symptoms of coronary ischemia, the most common of which is chest pain. Chest pain due to coronary ischemia commonly radiates to the arm or neck. Certain individuals such as women, diabetics, and the elderly may present with more varied symptoms. If blood flow through the coronary arteries is stopped completely, cardiac muscle cells may die, known as a myocardial infarction, or heart attack.
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction to the heart muscle. The most common symptom is retrosternal chest pain or discomfort that classically radiates to the left shoulder, arm, or jaw. The pain may occasionally feel like heartburn.
Abdominal aura, also known as visceral aura and epigastric aura, is a type of somatosensory aura that typically manifests as abdominal discomfort in the form of nausea, malaise, hunger, or pain. Abdominal aura is typically associated with epilepsy, especially temporal lobe epilepsy, and it can also be used in the context of migraine. The term is used to distinguish it from other types of somatosensory aura, notably visual disturbances and paraesthesia. The abdominal aura can be classified as a somatic hallucination. Pathophysiologically, the abdominal aura is associated with aberrant neuronal discharges in sensory cortical areas representing the abdominal viscera.
Kounis syndrome is defined as acute coronary syndrome caused by an allergic reaction or a strong immune reaction to a drug or other substance. It is a rare syndrome with authentic cases reported in 130 males and 45 females, as reviewed in 2017; however, the disorder is suspected of being commonly overlooked and therefore much more prevalent. Mast cell activation and release of inflammatory cytokines as well as other inflammatory agents from the reaction leads to spasm of the arteries leading to the heart muscle or a plaque breaking free and blocking one or more of those arteries.