Functional somatic syndrome (FSS) is a

syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek language, Greek σύνδρομον, meaning "concurrence". When a sy ...

in which any of a group of chronic symptoms occur with no identifiable organic cause.

Fibromyalgia Fibromyalgia (FM) is a functional somatic syndrome with symptoms of widespread chronic pain, accompanied by fatigue, sleep disturbance including awakening unrefreshed, and Cognitive deficit, cognitive symptoms. Other symptoms can include he ...

is the leading FSS condition, among many. FSS conditions are highly prevalent, but little is known about their etiology. Biological markers for the FSS diagnoses are non-existent, making the categorization difficult. Diagnosis is by exclusion.

Definition and Terminology

FSS refers to disturbances in bodily functioning where aetiology is unknown, including that psychogenesis is not assumed.

Related terms

" Medically unexplained physical symptoms" include FSS situations, but also situations where the symptoms are sporadic and where psychogenesis may be suspected. "Persistent physical symptoms" includes FSS situations but also situations where persistent physical symptoms are caused by a known illness, such as arthritis. In

somatic symptom disorder Somatic symptom disorder, also known as somatoform disorder or somatization disorder, is chronic somatization. One or more chronic physical symptoms coincide with excessive and maladaptive thoughts, emotions, and behaviors connected to those symp ...

chronic physical symptoms, which may or may not be linked to a known illness, coincide with excessive and maladaptive thoughts, emotions, and behaviors connected to those symptoms. In FSS these features are not present.

Signs and symptoms

Functional somatic syndromes are characterized by ambiguous,

non-specific symptoms Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

that appear in otherwise-healthy people. Overlap in symptomology exists across diagnoses, including gastrointestinal issues,

pain Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or res ...

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

, cognitive difficulties, and sleep difficulties. Some have proposed to group symptoms into clusters or into one general functional somatic disorder given the finding of correlations between symptoms and underlying etiologies.

Pre-diagnosis contact with health systems

A large (n = 43,676) 2020 study found that 5 years prior to diagnosis, FSS patients consulted more frequently for a range of psychological and somatic conditions than did controls. Around half this cohort were ME/CFS patients (normally not termed an FSS).

FSS conditions

FSS disorders include * fibromyalgia (FM), *

temporomandibular disorder Temporomandibular joint dysfunction (TMD, TMJD) is an umbrella term covering pain and dysfunction of the muscles of mastication (the muscles that move the jaw) and the temporomandibular joints (the joints which connect the mandible to the skul ...

, *

irritable bowel syndrome Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may ...

, * Electromagnetic hypersensitivity *

lower back pain Low back pain or wiktionary:lumbago#Etymology, lumbago is a common musculoskeletal disorders, disorder involving the muscles, nerves, and bones of the back, in between the lower edge of the ribs and the lower fold of the buttocks. Pain can var ...

, *

tension headache Tension headache, stress headache, or tension-type headache (TTH), is the most common type of primary headache. The pain usually radiates from the lower back of the head, the neck, the eyes, or other muscle groups in the body typically affecting b ...

, *atypical face pain, *non-cardiac chest pain, *

insomnia Insomnia, also known as sleeplessness, is a sleep disorder where people have difficulty sleeping. They may have difficulty falling asleep, or staying asleep for as long as desired. Insomnia is typically followed by daytime sleepiness, low ene ...

, *

palpitation Palpitations occur when a person becomes aware of their heartbeat. The heartbeat may feel hard, fast, or uneven in their chest. Symptoms include a very fast or irregular heartbeat. Palpitations are a sensory symptom. They are often described as ...

, *

dyspepsia Indigestion, also known as dyspepsia or upset stomach, is a condition of impaired digestion. Symptoms may include upper abdominal fullness, heartburn, nausea, belching, or upper abdominal pain. People may also experience feeling full earlier ...

, *

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to Balance disorder, disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a ...

. * certain claims of

food allergies A food allergy is an abnormal immune response to food. The symptoms of the allergic reaction may range from mild to severe. They may include itchiness, swelling of the tongue, vomiting, diarrhea, hives, trouble breathing, or low blood pressu ...

(when no true allergy can be demonstrated) * Gulf War syndrome * certain claims of

hypoglycaemia Hypoglycemia (American English), also spelled hypoglycaemia or hypoglycæmia (British English), sometimes called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's tria ...

(symptoms appearing when the blood sugar is normal) * Chronic Lyme disease *

Multiple chemical sensitivity Multiple chemical sensitivity (MCS) is an unrecognized and controversial diagnosis characterized by chronic symptoms attributed to exposure to low levels of commonly used chemicals. Symptoms are typically vagueness, vague and non-specific sympt ...

Sick building syndrome Sick building syndrome (SBS) is a condition in which people develop symptoms of illness or become infected with chronic disease from the building in which they work or reside. In scientific literature, SBS is also known as building-related illn ...

* Chronic whiplash

Overlap of FSS conditions

A large overlap of symptoms exist between the FSS diagnoses, causing high rates of comorbidity between them; the prevalence of comorbid FSS diagnoses ranges from 20% to 70%, while comorbid affective disorders with a fibromyalgia diagnosis ranges from 20% to 80%.

Prevalence

Studies have found prevalence in the general population of having at least one FSS of 16.3% (n = 9656), and 9.3% (n = 3054). Some 10% of the general population, and around 33% of adult patients in clinical populations, suffer from functional somatic symptoms.

Comorbidity

PTSD

Rates of PTSD are roughly 9.5–43.5% higher in people seeking treatment for a functional somatic syndrome as opposed to the general population.

Potential causes

Psychological factors

Patients with somatic syndromes such as fibromyalgia and irritable bowel syndrome have significantly higher rates of both physical and

sexual abuse Sexual abuse or sex abuse is abusive sexual behavior by one person upon another. It is often perpetrated using physical force, or by taking advantage of another. It often consists of a persistent pattern of sexual assaults. The offender is re ...

prior to the onset of their physiological symptoms, as well as higher rates of previous

emotional abuse Emotions are physical and mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is no scientific consensus on a definit ...

, emotional neglect, and physical neglect compared to the general population. Further, childhood trauma such as sexual abuse or

maltreatment Abuse is the act of improper usage or treatment of a person or thing, often to unfairly or improperly gain benefit. Abuse can come in many forms, such as: physical or verbal maltreatment, injury, assault, violation, rape, unjust practices, ...

can indicate an increased propensity for later somatic syndrome onset. "

Attentional bias Attentional bias refers to how a person's perception is affected by selective factors in their attention. Attentional biases may explain an individual's failure to consider alternative possibilities when occupied with an existing train of thought. ...

" has been posited as the psychological mechanism by which trauma and somatic symptoms are tied. The concept of attentional bias refers to the idea that traumatic events can cause individuals to become more attuned to their bodies, thus intensifying the perception of

, and other common somatic symptoms. The initial traumatic event is interpreted as a threat to the body, and therefore the stress-response of the body takes on a new, heightened awareness to any potential subsequent threats. This attentional bias leads to a " health anxiety," where the patient becomes increasingly concerned that common somatic symptoms are related to a physical disease or injury, and therefore, another potential bodily threat. An initial perception of lost control can further lead to this attentional bias; sense of control is negatively associated with symptom reporting, suggesting that somatic symptoms are more closely monitored when psychologically recovering from an incident of lost control. Functional Somatic Syndromes are thought to be a result of conditioned hyperarousal following a trauma; victims are conditioned to respond more sensitively to the somatic symptoms following a trauma by their attention to and reinforcement of the symptom existence. This feedback loop is similar to that of

panic disorder Panic disorder is a mental disorder, specifically an anxiety disorder, characterized by reoccurring unexpected panic attacks. Panic attacks are sudden periods of intense fear that may include palpitations, sweating, shaking, shortness of breath ...

, in which fear of a subsequent panic attack causes an increased hyper-vigilance towards, and exacerbation of, certain physiological symptoms, such as heart palpitations, dizziness, and breathlessness.

Biological factors

One hypothesis implicates the

hypothalamic–pituitary–adrenal axis The hypothalamic–pituitary–adrenal axis (HPA axis or HTPA axis) is a complex set of direct influences and feedback interactions among three components: the hypothalamus (a part of the brain located below the thalamus), the pituitary gland ( ...

(HPA axis) in the manifestation of somatic symptoms following trauma. The HPA axis plays a major role in moderating the body's

stress response The fight-or-flight or the fight-flight-freeze-or-fawn (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first describ ...

to both emotional and physical pain, relating to both the experience of psychological symptoms prevalent following trauma as well as the physiological symptoms prevalent in FSS conditions. When an individual experiences a traumatic event, the HPA-axis causes the increased release of cortisol, activating the sympathetic nervous pathway and causing negative feedback to be sent to the hypothalamus and pituitary gland. In people who have experienced significant trauma, this reaction can become dysfunctional and can cause a chronic decrease in cortisol production, though the rates of this decrease in cortisol levels varies across different types and frequencies of trauma.

Diagnosis

Diagnosis of a FSS is usually a

diagnosis of exclusion A diagnosis of exclusion or by exclusion (''per exclusionem'') is a diagnosis of a medical condition reached by a process of elimination, which may be necessary if presence cannot be established with complete confidence from history, examination o ...

, where physicians rule out other disorders that could explain the dysfunctions being experienced.

Management and Treatment

CBT can be helpful for FSS. Medications such as antidepressants may play a role.

History

The term functional somatic syndrome was used in a 1999 paper.

References

{{Reflist Rheumatology